boolean assignment in java

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Java methods, java classes, java file handling, java how to, java reference, java examples, java booleans.

Very often, in programming, you will need a data type that can only have one of two values, like:

TRUE / FALSE

For this, Java has a boolean data type, which can store true or false values.

Boolean Values

A boolean type is declared with the boolean keyword and can only take the values true or false :

Try it Yourself »

However, it is more common to return boolean values from boolean expressions, for conditional testing (see below).

Boolean Expression

A Boolean expression returns a boolean value: true or false .

This is useful to build logic, and find answers.

For example, you can use a comparison operator , such as the greater than ( > ) operator, to find out if an expression (or a variable) is true or false:

Or even easier:

In the examples below, we use the equal to ( == ) operator to evaluate an expression:

Real Life Example

Let's think of a "real life example" where we need to find out if a person is old enough to vote.

In the example below, we use the >= comparison operator to find out if the age ( 25 ) is greater than OR equal to the voting age limit, which is set to 18 :

Cool, right? An even better approach (since we are on a roll now), would be to wrap the code above in an if...else statement, so we can perform different actions depending on the result:

Output "Old enough to vote!" if myAge is greater than or equal to 18 . Otherwise output "Not old enough to vote.":

Booleans are the basis for all Java comparisons and conditions.

You will learn more about conditions ( if...else ) in the next chapter.

Test Yourself With Exercises

Fill in the missing parts to print the values true and false :

Start the Exercise

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Operators constitute the basic building block of any programming language. Java too provides many types of operators which can be used according to the need to perform various calculations and functions, be it logical, arithmetic, relational, etc. They are classified based on the functionality they provide.

Types of Operators:

Arithmetic Operators
Unary Operators
Assignment Operator
Relational Operators
Logical Operators
Ternary Operator
Bitwise Operators
Shift Operators

This article explains all that one needs to know regarding Assignment Operators.

Assignment Operators

These operators are used to assign values to a variable. The left side operand of the assignment operator is a variable, and the right side operand of the assignment operator is a value. The value on the right side must be of the same data type of the operand on the left side. Otherwise, the compiler will raise an error. This means that the assignment operators have right to left associativity, i.e., the value given on the right-hand side of the operator is assigned to the variable on the left. Therefore, the right-hand side value must be declared before using it or should be a constant. The general format of the assignment operator is,

Types of Assignment Operators in Java

The Assignment Operator is generally of two types. They are:

1. Simple Assignment Operator: The Simple Assignment Operator is used with the “=” sign where the left side consists of the operand and the right side consists of a value. The value of the right side must be of the same data type that has been defined on the left side.

2. Compound Assignment Operator: The Compound Operator is used where +,-,*, and / is used along with the = operator.

Let’s look at each of the assignment operators and how they operate:

1. (=) operator:

This is the most straightforward assignment operator, which is used to assign the value on the right to the variable on the left. This is the basic definition of an assignment operator and how it functions.

Syntax:

Example:

2. (+=) operator:

This operator is a compound of ‘+’ and ‘=’ operators. It operates by adding the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left.

Note: The compound assignment operator in Java performs implicit type casting. Let’s consider a scenario where x is an int variable with a value of 5. int x = 5; If you want to add the double value 4.5 to the integer variable x and print its value, there are two methods to achieve this: Method 1: x = x + 4.5 Method 2: x += 4.5 As per the previous example, you might think both of them are equal. But in reality, Method 1 will throw a runtime error stating the “i ncompatible types: possible lossy conversion from double to int “, Method 2 will run without any error and prints 9 as output.

Reason for the Above Calculation

Method 1 will result in a runtime error stating “incompatible types: possible lossy conversion from double to int.” The reason is that the addition of an int and a double results in a double value. Assigning this double value back to the int variable x requires an explicit type casting because it may result in a loss of precision. Without the explicit cast, the compiler throws an error. Method 2 will run without any error and print the value 9 as output. The compound assignment operator += performs an implicit type conversion, also known as an automatic narrowing primitive conversion from double to int . It is equivalent to x = (int) (x + 4.5) , where the result of the addition is explicitly cast to an int . The fractional part of the double value is truncated, and the resulting int value is assigned back to x . It is advisable to use Method 2 ( x += 4.5 ) to avoid runtime errors and to obtain the desired output.

Same automatic narrowing primitive conversion is applicable for other compound assignment operators as well, including -= , *= , /= , and %= .

3. (-=) operator:

This operator is a compound of ‘-‘ and ‘=’ operators. It operates by subtracting the variable’s value on the right from the current value of the variable on the left and then assigning the result to the operand on the left.

4. (*=) operator:

This operator is a compound of ‘*’ and ‘=’ operators. It operates by multiplying the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left.

5. (/=) operator:

This operator is a compound of ‘/’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the quotient to the operand on the left.

6. (%=) operator:

This operator is a compound of ‘%’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the remainder to the operand on the left.

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Booleans in Java: From Basics to Advanced

simple_binary_choice_symbols_representing_java_boolean_values

Are you finding it challenging to work with boolean in Java? You’re not alone. Many developers find themselves puzzled when it comes to handling boolean data types in Java, but we’re here to help.

Think of Java’s boolean as a light switch – it can only be in one of two states, true or false. This simple yet powerful feature provides a versatile and handy tool for various tasks, especially in control structures.

In this guide, we’ll walk you through the process of working with boolean in Java , from declaration and initialization to more advanced uses in control structures. We’ll cover everything from the basics of boolean data types to more advanced techniques, as well as alternative approaches.

Let’s get started and master boolean in Java!

TL;DR: How Do I Use Boolean in Java?

In Java, you can declare a boolean variable and assign it a value of true or false: boolean isJavaDifficult = false This is a fundamental concept in Java that is used in various control structures.

Here’s a simple example:

In this example, we declare a boolean variable isJavaFun and assign it a value of true . We then print the value of isJavaFun , which outputs true .

This is just a basic way to use boolean in Java, but there’s much more to learn about using boolean in control structures and other advanced scenarios. Continue reading for more detailed information and advanced usage scenarios.

Table of Contents

Declaring and Initializing Boolean Variables in Java

Leveraging boolean in control structures, exploring the java boolean class, common pitfalls and solutions with java boolean, understanding java boolean fundamentals, the relevance of boolean in larger java programs, exploring related concepts, wrapping up: mastering boolean in java.

In Java, declaring a boolean variable is straightforward. You use the boolean keyword followed by the variable name. Let’s dive into a simple example:

In this example, we’ve declared a boolean variable isLearningJava but haven’t assigned a value yet. By default, a boolean variable is false if you don’t assign it a value.

To initialize a boolean variable, you assign it a value of true or false .

Now, isLearningJava is not just declared, but also initialized with the value true .

The Power of Boolean

Booleans are simple, yet powerful. They are primarily used in control flow statements like if , while , and for loops. Booleans can help your program make decisions based on certain conditions.

Potential Pitfalls with Boolean

While booleans are easy to use, they can lead to confusing code if not used properly. For instance, using boolean variables that have not been initialized can lead to unexpected results. Always ensure your boolean variables are properly initialized before using them in your code.

In Java, boolean expressions play a critical role in control structures such as if-else statements and while loops. Let’s explore how to use boolean expressions in these structures.

If-Else Statements with Boolean

In an if-else statement, a boolean condition determines the flow of execution. If the condition is true , the code within the if block executes. If the condition is false , the else block executes (if present).

Here’s an example:

In this example, since isLearningJava is true , the message “Keep up the good work!” is printed.

While Loops with Boolean

A while loop continues to execute as long as the boolean condition remains true . Here’s an example:

In this example, the while loop continues to print and increment the count as long as count < 5 is true . Once count reaches 5, the condition becomes false , and the loop terminates.

Java provides a Boolean class, which is a part of java.lang package. It wraps the boolean primitive data type into an object. The Boolean class offers a range of methods to help you manipulate boolean values.

Using Boolean Class Methods

Let’s look at a few examples of these methods. The Boolean.valueOf() method returns the Boolean value of the specified string. If the string argument is not null and is equal, ignoring case, to the string “true”, it returns true . Otherwise, it returns false .

In this example, Boolean.valueOf("True") returns true , and Boolean.valueOf("False") returns false .

Advantages of Using Boolean Class

The Boolean class has several advantages. It provides useful constants and methods for dealing with boolean values. It also allows null values, unlike the primitive boolean type.

Disadvantages of Using Boolean Class

However, it’s important to remember that objects of the Boolean class are immutable. Once a Boolean object is created, it cannot change its value. This is unlike the primitive boolean type, which can be reassigned freely. Also, comparing Boolean objects using '==' can lead to unexpected results, as it compares object references, not their values.

Working with boolean in Java can sometimes lead to unexpected results. Let’s discuss some common issues and their solutions.

Misunderstanding '==' and ‘equals()’

One common mistake when working with the Boolean class is misunderstanding the difference between '==' and ‘equals()’. The '==' operator checks if two references point to the same object, whereas ‘equals()’ checks if the two objects have the same value.

In this example, bool1 == bool2 returns false because bool1 and bool2 are different objects. However, bool1.equals(bool2) returns true because both objects have the same value ( true ).

Uninitialized Boolean Variables

Another common issue is using a boolean variable that has not been initialized. In Java, local variables are not given a default value.

In this example, trying to print myBool results in a compilation error because myBool has not been initialized. Always ensure your boolean variables are properly initialized before using them.

In Java, a boolean is a primitive data type that can only hold one of two possible values: true or false . This binary nature makes boolean data types extremely useful in control structures, where they can dictate the flow of a program based on certain conditions.

In this example, the boolean variable isRaining is false , so the program prints “No need for an umbrella.” If isRaining were true , the program would print “Better take an umbrella!”

Primitive Boolean vs Boolean Class

Java provides two ways to work with boolean values: the primitive boolean data type and the Boolean class. The primitive boolean data type is simple and efficient, but it lacks the object-oriented features provided by the Boolean class.

The Boolean class, on the other hand, wraps a value of the primitive type boolean in an object. An object of type Boolean contains a single field, whose type is boolean . In addition, this class provides several useful constants and methods for manipulating boolean values.

In this example, we use the Boolean class instead of the primitive boolean data type. The result is the same, but notice the use of the equals() method for comparison.

In larger Java programs, boolean plays a significant role in conditional statements, loops, and error handling. The ability of boolean to hold one of two values, true or false , makes it an essential tool for controlling program flow.

Boolean in Conditional Statements

In conditional statements like if , else if , and else , boolean expressions determine which block of code executes. For example:

Boolean in Loops

Boolean is also used in loops such as while and for . A boolean condition controls when the loop starts and ends. For example:

Boolean in Error Handling

In error handling, boolean can be used to indicate the success or failure of a method. For example:

While boolean is a fundamental concept in Java, it’s just one piece of the puzzle. To write effective Java programs, you should also understand related concepts like control structures and exception handling in Java.

Further Resources for Mastering Java Boolean

To deepen your understanding of boolean in Java, here are some additional resources:

IOFlood’s Java Primitive Data Types Guide explores Java’s default values for uninitialized primitive variables.

Java Float – Explore the Java float data type for representing single-precision floating-point numbers.

Int Data Type in Java – Learn about the range and memory allocation of int variables in Java.

Java Boolean Documentation – Official Java documentation for the Boolean class.

Java Tutorials by Oracle – Comprehensive tutorials on various aspects of Java, including boolean and control structures.

Java Programming Basics by Udacity – An online course that covers the basics of Java programming, including boolean.

In this comprehensive guide, we’ve embarked on a journey to understand and master the use of boolean in Java, from its declaration and initialization to its role in control structures.

We began with the basics, explaining how to declare and initialize boolean variables in Java. We then delved into more advanced topics, such as using boolean expressions in control structures like if-else statements and while loops. We also explored the Boolean class in Java and its methods, providing a more object-oriented approach to manipulating boolean values.

Along the way, we addressed common issues that you might encounter when working with boolean in Java, such as the difference between '==' and ‘equals()’ when comparing Boolean objects, and the importance of initializing boolean variables. We provided solutions and workarounds for these issues, helping you to avoid these pitfalls in your coding journey.

Whether you’re just starting out with Java or you’re looking to deepen your understanding of boolean, we hope this guide has shed light on the power and versatility of boolean in Java.

Understanding and using boolean effectively is a key skill in Java programming. With this guide, you’re well on your way to mastering boolean in Java. Happy coding!

About Author

Gabriel Ramuglia

Gabriel is the owner and founder of IOFLOOD.com , an unmanaged dedicated server hosting company operating since 2010.Gabriel loves all things servers, bandwidth, and computer programming and enjoys sharing his experience on these topics with readers of the IOFLOOD blog.

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Java Boolean: A Beginner’s Guide

How to use booleans in java.

True or false. We’re not talking about a question on a standardized test. True and false are the values that can be stored inside the Boolean data type.

In programming, Booleans are used to control the flow of a program. They are also used to make comparisons between values.

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In this guide, we’re going to talk about the basics of how Booleans work. We’ll discuss how to make comparisons with Booleans, and how to use logical operators. Let’s get started!

What is a Java Boolean?

A boolean is a data type that can store one of two values: true and false.

Booleans are a key part of logical operations in mathematics. They’re useful when the answer to a problem can only be one of two values. A boolean value could represent on or off, true or false, yes or no, or any other situation where only two possible outcomes are valid.

The Boolean data type is capitalized when we talk about it. This is because it was named after the mathematician George Boole, who played a key role in the fields of logic and algebra. However, when you are declaring a boolean, you should use lowercase.

In Java, booleans are declared using the boolean keyword. Let’s declare a boolean which tracks whether a coffee house has its premium beans in stock:

Our code returns: true. We’ve stored the value “true” inside the variable “premiumBeans”. Notice that we have declared our boolean using the boolean keyword, which appears in lowercase.

Boolean objects represent false or true values.

Making Comparisons Using Booleans

The Boolean data type is particularly useful when making comparisons.

This is because when you are comparing two values, a comparison can only be true or false. A string can only be equal to or not equal to another number; a number can only be less than or greater than another number.

Let’s demonstrate how this works with an example. We’re going to write a program which checks whether a child at a theme park is old enough to go on a ride. We’ll start by declaring two variables:

The variable “minimumAge” tells us the minimum age you have to be to go on a ride. The variable “customerAge” is the age of the child who wants to go on the ride.

To check whether the customer is old enough to go on the ride, we can use a comparison operator:

Our code returns:

We have declared a new variable called “isOldEnough”. This variable represents the specified boolean which is calculated using our comparison statement. We check whether the customer’s age is greater than or equal to the minimum age. If it is, isOldEnough will be equal to true; otherwise, it will be false.

15 (customerAge) is greater than 12 (minimumAge). This means that our expression evaluates to true, and so our boolean object represents the value true.

We can use any Java comparison operator to perform a comparison:

==: Equal to
!=: Not equal to
>: Greater than
<: Less than
>=: Greater than or equal to
<=: Less than or equal to

Consider the following code:

In this code, we have compared whether or not the customer’s age is equal to the minimum age. These numbers are not equal, so our Boolean expression evaluates to false:

When you are comparing to see whether two values are equal, you must use two equals signs (==). One equals sign is used to assign a value to a variable in Java; two equals signs denote that you want to make a comparison.

Using Boolean Logical Operators

Booleans can be used with Java’s logical operators to determine whether multiple expressions are met. These operators will return a boolean value: true or false.

There are three logical operators:

&& (and): Returns “true” if both values are true
! (not): Returns “true” if a value is false
|| (or): Returns “true” if at least one value is true

Let’s use an example to show these operators in action. For example, suppose that we’re building a program that evaluates whether a customer should receive a discount on a purchase.

A discount should be given if a user’s purchase is over $40 and the user is a loyalty card member. We could check for these conditions using this statement:

Our code returns: true. Our code evaluates three expressions:

Is purchasePrice greater than 40?
Is isLoyaltyCustomer equal to true?
Is purchasePrice greater than 40 and is isLoyaltyCustomer equal to true?

If all of these conditions are met – which they are in this case – true is returned. Otherwise, false is returned.

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Let’s say that we want to give our discount to people who make a purchase greater than $40 or who are loyalty card members. We could do this by changing our logical operator to “||” (the “or” operator) instead of “&&” (the “and” operator):

Our code returns: true. Our program checks:

Is purchasePrice greater than 40 or is isLoyaltyCustomer equal to true?

Only one of the two conditions we have specified needs to be met for true to be returned. In this case, isLoyaltyCustomer is equal to true, so our code returns true.

We can use the not operator to check whether a value is false. Suppose we only want to give the discount to people who are not loyal customers because they already receive a spare discount. We could enforce this using the following code:

In this code, we check if “isLoyaltyCustomer” is not true. “isLoyaltyCustomer” is equal to true, so our code returns false.

Using Booleans with Conditionals

Booleans are often used with conditional statements such as an if statement.

A conditional will evaluate a statement down to a true or false value. If a condition is true, the code within a conditional block will run; otherwise, that code will not run.

Let’s say that we want to print a message to the console if a customer is eligible for a discount. A customer is eligible for a discount only if they are a loyalty customer:

Our code returns a string object:

Our code checks to see whether the value of “isLoyaltyCustomer” is equal to true. It is, and so the code within our if statement is run.

If our customer was not a loyalty card holder, this statement would evaluate to false. In this case, the contents of our else statement would be run.

Booleans allow you to store true or false values in your code. When used with comparison operators, you can use a boolean to evaluate a statement.

You can use logical operators with a boolean to determine if multiple conditions are met, if one of multiple conditions are met, or if a condition is not met. Booleans are often used with conditional statements such as an if statement to evaluate an expression.

Now you’re ready to work with booleans in Java like a professional!

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Java Booleans Explained [Easy Examples]

Bashir Alam

September 1, 2021

Introduction to Java booleans

Java Boolean is an inbuilt class that wraps are used for wrapping the value of primitive data type, i.e. boolean in an object. The boolean class contains two values, i.e. true or false . Java provides a wrapper class Boolean in java.lang package. The Boolean class wraps a value of the primitive type boolean in an object. An object of type Boolean contains a single field, whose type is boolean. In this tutorial, we will learn about java booleans in detail. We will see how we can use booleans in conditions, loops, and functions. Moreover, we will also cover some of the java operators that return a boolean value, along with examples. All in all, this will be one of the detailed tutorials about java booleans.

Getting started with Java booleans

The Boolean class is simply a wrapper class for the primitive type boolean. It wraps the boolean primitive value to an object. An object of type Boolean contains a single field whose type is boolean. The simple syntax of creating a boolean object from a boolean class looks like this;

Now let us create a boolean object and then use it in our java code. See the example below:

Notice that we get true for the first three cases which means that the java boolean class is not case sensitive. It will return true does not matter which alphabetic case we use. And it will return false if we provide an argument other than true , that is why for the last case we get false .

Logical operators and Java booleans

We know that the logical operators in Java return booleans value. You can learn more about logical operators . There are three logical operators in Java which are as follow:

&& ; Return true if both the conditions are true.
|| ; Return true if any of the conditions are true.
! ; Return true if the condition is not true

Now, in this section, we will take examples of each of these operators and get a boolean value.

Example-1 AND operator and Java booleans

AND operator returns boolean value true if both the conditions are satisfied, otherwise, it will return the boolean value false . See the example below which uses the logical AND operator.

Notice that the logical AND operator only returns true if both the conditions are true , else it returns false .

Example-2 OR operator and Java booleans

Java logical OR operator returns true if any of the conditions are true and only returns false if all the conditions are false . See the example below:

Notice that we only get false when both of the conditions were False .

Example-3 NOT operator and Java booleans

NOT operator simply reverses the condition, which means if the condition is true , it will return false and if the condition is false it will return true . See the example below:

Notice that we get true for the False condition and vice versa.

Rational operators and Java booleans

Relational operator refers to the relationships that values or operands can have with one another. Java provides 6 relational operators for comparing numbers and characters. They are mostly used for comparison purposes. After the comparison, they return the result in boolean datatype. The rational operators in Java are listed below:

== : Return true if both the operands are equal.
!= ; Return true if both the operands are not equal.
< ; Return true if left-hand side operand is less than right side one.
> ; Return true if right-hand side operand is less than left side one.
<= ; Return true if left side operand is less than or equal to right side one.
>= ; Return true if right side operand is less than or equal to left side one.

In this section, we will take these rational operations and see how and when they return java booleans.

Example-1 Equal and not equal assignment operators and Java booleans

Equal to the operator ( == ) return true if both the operands are equal. It can be used to compare lists, int, float dict, strings, and other data types. While not equal to ( != ) operator returns true if both of the operands are not equal. It can also be used to compare various data types.

Now let us take an example and see how they are used to compare data types. See the example below:

Example-2 Greater than or less than operators and Java booleans

Greater than ( > ) operator returns true if the left side is greater than the right side one else, it returns false . Similarly, the less than ( < ) operator returns true if the left side is smaller than the right side one, else it will also return false .

See the example below which uses these operators.

Notice that we get the result accordingly.

Java booleans in conditional statements

One of the important uses of java booleans is in conditional statements. If the condition is true , the java statements inside the condition will be executed and if the condition is false then none of the statements inside the condition will be executed. So the java booleans are important parts of if-else statements. In this section, we will be discussing how the java booleans control the if-else statements in the java programming language.

Example-1 Direct use of java booleans

First, let us directly use the java booleans in our conditional statements so it will give us a depth understanding of how it works in if-else statements. See the example below:

Notice that the first condition was true so it was executed. Now if we make the first condition false , then the else statement will be executed. See the example below:

Example-2 Using conditions that return Java booleans

We already had discussed some of the java operators that return booleans in a couple of sections above. Now, let us see how we can use those operators in java conditions and executed the required statements only. See the example below:

Notice that the operators in the if and else if statements, return false because the conditions were false and it only executes the last statement.

Java booleans in while loop

Java while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement. ... If the condition evaluates to true then we will execute the body of the loop and go to update expression inside the loop. In this section let us use java while loop with java booleans.

Example-1 Direct use of java booleans in while loop

If we use direct true in the while loop without any break statement or condition, it will be an infinity loop and if we use direct false in our while loop, then the loop will never be executed. See the example below which uses direct true boolean in while loop:

This is an infinity loop because the condition is never going to be false and we don't have any break statements as well. This kind of loop is prohibited in any programming language because it returns unexpected values. It is always recommended to use either break or conditional statements inside loops.

Now let us see what will happens if we use direct false booleans value while loop. See the example below:

This time we will get an error because we had used a direct the false boolean value and java will through an error saying that the code inside the loop is not reachable. See the error below:

Example-2 using condition in while loop

Now let us use a condition that returns true if it is true and returns false if it becomes false . See the example below:

Notice that as the condition was true , the loop was executing and as soon as the condition becomes false , the loop stops executing.

In Java, the boolean keyword is a primitive data type. It is used to store only two possible values, either true or false . It specifies 1-bit of information and its "size" can't be defined precisely. The boolean keyword is used with variables and methods. Its default value is false . It is generally associated with conditional statements. In this tutorial, we learned about java booleans in detail.

We learned how we can create a java boolean object from the boolean class in java by taking examples. Moreover, we also learned about the java operators that return boolean values depending on the condition and we also discussed how booleans play important role in java while loop. All in all, this tutorial, contains all the information that you need to start working with java booleans.

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Understanding Default Boolean Values in Java – A Guide for Beginners

Default boolean value in java explained.

Boolean values are an integral part of programming languages like Java. They are used to represent two states: true or false. Understanding default boolean values is crucial when working with Java to prevent unintended behavior and enhance code efficiency.

Definition of Default Values

Default values refer to the initial values assigned to variables in Java when no explicit value is provided. These values are automatically assigned by the Java compiler based on the data type of the variable. For boolean variables, the default value is “false.”

Explanation of “False” as the Default Value

By default, when a boolean variable is declared in Java without initializing it, its value will be set to false. This means that if you access a boolean variable before assigning a value to it, it will be automatically considered as false. For example:

In this example, the variable “isFlag” is not assigned a value, and therefore, it defaults to false. It is important to note that default boolean values are not specific to Java; they exist in many other programming languages as well.

Common Misconceptions about Default Boolean Values

There are a few misconceptions and pitfalls related to default boolean values in Java. Let’s address some of the most common ones:

Misconception #1: Default boolean values can be changed to “true” by default

This is incorrect. In Java, the default boolean value is always “false.” This is a fundamental behavior of the language and cannot be modified.

Misconception #2: All variables have default values

Although most variables in Java have default values, it is essential to note that local variables (variables declared inside methods or blocks) do not have default values. They must be explicitly initialized before use.

Practical Examples

Understanding how default boolean values are used in Java programs can give you a better grasp of their significance. Let’s explore some practical examples:

Default Initialization of Boolean Variables

When declaring boolean variables, you can leave them uninitialized if you want their default values to be assigned automatically. This can save time and make your code more concise. For instance:

In this example, “isValid” will have the default value of false, while “isAllowed” is explicitly assigned a value of true. Initializing boolean variables explicitly is recommended for improved code readability and to avoid potential confusion.

Boolean Expressions and Conditions

Boolean values play a crucial role in controlling program flow and decision making. They are commonly used in conditional statements (e.g., if-else statements, while loops, etc.) and boolean expressions. The default value of false ensures that if a condition is not met, the corresponding block of code will not be executed. Consider the following example:

Here, the default value of false ensures that the code block for the “permission denied” scenario is executed in case “hasPermission” is not explicitly set to true.

Best Practices and Tips

While default boolean values can be beneficial, some best practices can help you avoid unforeseen issues and enhance the quality of your code:

Initializing Boolean Variables Explicitly

To prevent unintended behavior or inconsistencies, it is recommended to initialize boolean variables explicitly. By assigning an initial value explicitly, you ensure that the variable starts with the desired value. This can help in avoiding bugs caused by relying on default values.

Using Default Boolean Values to Simplify Code

Default boolean values can simplify your code by eliminating unnecessary assignments or comparisons. For example:

In this example, the explicit comparison “isReady == true” is redundant since “isReady” is already a boolean value. By using the default boolean value directly, the code becomes more concise and easier to read.

Common Pitfalls and Misconceptions

Despite the straightforward nature of default boolean values, there are still some common pitfalls and misconceptions to be aware of:

Misunderstanding Default Boolean Values in Different Contexts

One common mistake is mistaking default values for user-defined values. It is crucial to differentiate between an explicitly assigned value and the default value assigned automatically. Failure to do so can lead to incorrect program behavior and logic errors.

Another misconception is making incorrect assumptions in conditional statements. Boolean conditions should be explicitly checked against the desired value or expression to ensure the correct execution flow.

In conclusion, default boolean values in Java are automatically assigned as “false” when a value is not explicitly provided. Understanding default boolean values is essential for both beginners and experienced Java programmers. It helps prevent unintended behavior and enables more efficient code writing. By following best practices, avoiding common pitfalls, and utilizing default boolean values effectively, you can enhance the quality of your Java programs.

To dive deeper into boolean values and their usage in Java, continue exploring the Java documentation and engage in practical programming exercises. Building a solid understanding of boolean values will serve as a foundation for writing reliable and efficient Java code.

The Ultimate Guide to Using Boolean in C – Everything You Need to Know
Understanding the Boolean Type in C – A Comprehensive Guide
Comparing Boolean Values in Java – A Comprehensive Guide and Examples
Java Boolean Default – Understanding the Default Values and Use Cases in Java Programming
Understanding Boolean Default Values – Everything You Need to Know

Class Boolean

java.lang.Object
java.lang.Boolean

In addition, this class provides many methods for converting a boolean to a String and a String to a boolean , as well as other constants and methods useful when dealing with a boolean .

Field Summary

Constructor summary, method summary, methods declared in class java.lang. object, field detail, constructor detail, method detail, parseboolean.

Example: Boolean.parseBoolean("True") returns true . Example: Boolean.parseBoolean("yes") returns false .

booleanValue

If there is no property with the specified name, or if the specified name is empty or null, then false is returned.

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Java 22 and IntelliJ IDEA

Java 22 is here, fully supported by IntelliJ IDEA 2024.1 , allowing you to use these features now!

Java 22 has something for all – from new developers to Java experts, features related to performance and security for big organizations to those who like working with bleeding edge technology, from additions to the Java language to improvements in the JVM platform, and more.

It is also great to see how all these Java features, release after release, work together to create more possibilities and have a bigger impact on how developers create their applications that address existing pain points, perform better and are more secure.

This blog post doesn’t include a comprehensive coverage of all the Java 22 features. If you are interested in that, I’d recommend you to check out this link to know everything about what’s new and changing in Java 22, including the bugs.

In this blog post, I’ll cover how IntelliJ IDEA helps you get started, up and running with some of the Java 22 features, such as, String Templates , Implicitly Declared Classes and Instance Main Methods , Statements before super() , and Unnamed variables and patterns .

Over the past month, I published separate blog posts to cover each of these topics in detail. If you are new to these topics, I’d highly recommend you check out those detailed blog posts (I’ve included their links in the relevant subsections in this blog post). In this blog post, I’ll cover some sections from those blog posts, especially how IntelliJ IDEA supports them. Let’s start by configuring IntelliJ IDEA to work with the Java 22 features.

IntelliJ IDEA Configuration

Java 22 support is available in IntelliJ IDEA 2024.1 Beta . The final version will release soon in March 2024.

In your Project Settings, set the SDK to Java 22. For the language level, select ‘22 (Preview) – Statements before super(), string templates (2nd preview etc.)’ on both the Project and Modules tab, as shown in the below settings screenshot:

If you do not have Java 22 downloaded to your system yet, don’t worry; IntelliJ IDEA has your back! You could use the same Project settings window, select ‘Download JDK’, after you click on the drop down next to SDK. You’ll see the below popup that would enable you to choose from a list of vendors (such as Oracle OpenJDK, GraalVM, Azul Zulu and others):

With the configuration under our belt, let’s get started with covering one of my favorite new features, that is, String Templates.

String Templates (Preview Language feature) The existing String concatenation options are difficult to work with and could be error prone; String templates offer a better alternative, that is, String interpolation with additional benefits such as validation, security and transformations via template processors.

Please check out my detailed blog post on this topic: String Templates in Java – why should you care? if you are new to this topic. It covers all the basics, including why you need String Templates, with multiple hands-on examples on built-in and user defined String processors.

IntelliJ IDEA can highlight code that could be replaced with String Templates Let’s assume you defined the following code to log a message that combines string literals and variable values using the concatenation operator:

The output from the preceding code could be an issue if you miss adding spaces in the String literals. The code isn’t quite easy to read or understand due to multiple opening and closing double quotes, that is, " and the + operator, and it would get worse if you add more literals, or variable values to it.

You could replace the preceding code with either StringBuilder.append() , String.format() or String.formatted() method or by using the class MessageFormat (as shown in my detailed blog post on this topic), but each of these methods have their own issues.

Don’t worry; IntelliJ IDEA could detect such code, suggest that you could replace it with String template, and do that for you, as shown below. It doesn’t matter if you are not even aware of the syntax of the String templates, IntelliJ IDEA has your back 🙂

Embedded expressions in String Templates and IntelliJ IDEA The syntax to embed a remplate expression (variable, expressible or a method call) is still new to what Java developers are used to and could be challenging to use without help. Don’t worry, IntelliJ IDEA has your back!

Each embedded expression must be enclosed within \{}. When you type \{, IntelliJ IDEA adds the closing ‘}’ for you. It also offers code completion to help you select a variable in scope, or any methods on it. If the code that you insert doesn’t compile, IntelliJ IDEA will highlight that too (as a compilation error), as shown in the following gif:

Using String Templates with Text Blocks Text blocks are quite helpful when working with string values that span multiple lines, such as, JSON, XML, HTML, SQL or other values that are usually processed by external environments. It is common for us Java developers to create such string values using a combination of string literals and variable values (variables, expressions or method calls).

The example below shows how IntelliJ IDEA could detect and create a text block using String templates for multiline string values that concatenates string literals with variable values. It also shows how IntelliJ IDEA provides code completion for variable names within such blocks. When you type in \{ , IntelliJ IDEA adds } . As you start typing the variable name countryName , it shows the available variables in that context:

Language injection and String Templates You could also inject a language or a reference in string values that spans single line or multiple lines, such as, a text block. By doing so, you get comprehensive coding assistance to edit the literal value. You could avail of this feature temporarily or permanently by using the @Language annotation, as shown below:

You can check out this link for detailed information on the benefits and usage of injecting language or reference in IntelliJ IDEA.

Predefined Template Processors With the String templates, you get access to predefined processors like the STR , FMT and RAW . I’d highly recommend you to check out my detailed blog post on String templates for multiple hands-on examples on it.

Custom Template Processor

Let’s work with a custom String template that isn’t covered in my previous blog post.

Imagine you’d like to create an instance of a record, say, WeatherData , that stores the details of the JSON we used in the previous section. Assume you define the following records to store this weather data represented by the JSON in the previous section:

You could create a method to return a custom String template that would process interpolated string, accept a class name ( WeatherData for this example) and return its instance:

Depending on the logic of your application, you might want to escape, delete or throw errors for the special characters that you encounter in the the JSON values interpolated via template expressions, as follows (the following method chooses to escape the special characters and include them as part of the JSON value):

You could initialize and use this custom JSON template processor as below. Note how elegant and concise the solution is with a combination of textblocks and String templates. The JSON is easy to read, write and understand (thanks to text blocks). The template expressions make it clear and obvious about the sections that are not constants and would be injected by the variables. At the end, the custom template processor WEATHER_JSON would ensure the resultant JSON is validated according to the logic you defined and returns an instance of WeatherData (doesn’t it sound magical?) :

Do not miss to check out my detailed blog post on this topic: String Templates in Java – why should you care? to discover how you could use the predefined String templates like FMT , to generate properly formatted receipts for, say, your neighborhood stationery store, or, say encode and decode combinations like :) or :( to emojis like 🙂 or ☹️. Does that sound fun to you?

Implicitly Declared Classes and Instance Main Methods (Preview language feature)

Introduced as a preview language feature in Java 21, this feature is in its second preview in Java 22.

It would revolutionize how new Java developers would get started learning Java. It simplifies the initial steps for students when they start learning basics, such as variable assignment, sequence, conditions and iteration. Students no longer need to declare an explicit class to develop their code, or write their main() method using this signature – public static void main(String []) . With this feature, classes could be declared implicitly and the main() method can be created with a shorter list of keywords.

If you are new to this feature, I’d highly recommend you to check out my detailed blog post: ‘HelloWorld’ and ‘main()’ meet minimalistic on this feature. In this blog post, I’ll include a few of the sections from it.

Class ‘HelloWorld’ before and after Java 21

Before Java 21, you would need to define a class, say, HelloWorld , that defined a main() method with a specific list of keywords, to print any text, say, ‘Hello World’ to the console, as follows:

With Java 21, this initial step has been shortened. You can define a source code file, say, HelloWorld.java, with the following code, to print a message to the console (it doesn’t need to define a class; it has a shorter signature for method main() ):

The preceding code is simpler than what was required earlier. Let’s see how this change could help you focus on what you need, rather than what you don’t.

Compiling and executing your code

Once you are done writing your code, the next step is to execute it.

On the command prompt, you could use the javac and java commands to compile and execute your code. Assuming you have defined your code in a source code file HelloWorld.java, you could use the following commands to run and execute it:

Since Java 11, it is possible to skip the compilation process for code defined in a single source code file, so you could use just the second command (by specifying the name of the source code file, as follows):

However, since instance main methods and implicit classes is a preview language feature, you should add the flag --enable-preview with --source 22 with these commands, as follows:

Sooner or later, you might switch to using an IDE to write your code. If you wish to use IntelliJ IDEA for creating instance main methods, here’s a quick list of steps to follow. Create a new Java project, select the build system as IntelliJ (so you could use Java compiler and runtime tools), create a new file, say, HelloWorld.java with your instance main method and set the properties to use Java 22, before you run your code, as shown in the following gif (It could save you from typing out the compilation/ execution commands on the command prompt each time you want to execute your code):

Are you wondering if it would be better to create a ‘Java class’ instead of a ‘File’ in the ‘src’ folder? The option of selecting a Java class would generate the body of a bare minimum class, say, public class HelloWorld { } . Since we are trying to avoid unnecessary keywords in the beginning, I recommended creating a new ‘File’ which wouldn’t include any code.

What else can main() do apart from printing messages to the console?

As included in my detailed post on this topic , I included multiple hand-on examples to show what you could achieve via just the main() method:

Example 1. Variable declarations, assignments and simple calculations
Example 2. Print patterns, such as, big letters using a specified character
Example 3. Animating multiline text – one word at a time
Example 4. Data structure problems
Example 5. Text based Hangman game

The idea to include multiple examples as listed above is to demonstrate the power of sequence, condition and iteration all of which can be included in the main() method, to build good programming foundations with problem solving skills. By using the run command or the icon to run and execute their code in IntelliJ IDEA, new programmers reduce another step when getting started.

Changing an implicit class to a regular class

When you are ready to level up and work with other concepts like user defined classes, you could also covert the implicit classes and code that we used in the previous examples, to regular classes, as shown below:

What happens when you create a source code file with method main(), but no class declaration?

Behind the scenes, the Java compiler creates an implicit top level class, with a no-argument constructor, so that these classes don’t need to be treated in a way that is different to the regular classes.

Here’s a gif that shows a decompiled class for you for the source code file AnimateText.java:

Variations of the main method in the implicit class

As we are aware, a method can be overloaded. Does that imply an implicit class can define multiple main methods? If yes, which one of them qualifies as the ‘main’ method? This is an interesting question. First of all, know that you can’t define a static and non-static main method with the same signature, that is, with the same method parameters. The following method are considered valid main() methods in an implicit class:

If there is no valid main method detected, IntelliJ IDEA could add one for you, as shown in the following gif:

Educators could use this feature to introduce other concepts to the students in an incremental way

If you are an educator, you could introduce your students to other commonly used programming practices, such as creating methods- that is delegating part of your code to another method and calling it from the main method. You could also talk about passing values vs. variables to these methods.

The following gif shows how to do it:

Statements before super() – a preview language feature

Typically, we create alternative solutions for tasks that are necessary, but not officially permitted. For instance, executing statements before super() in a derived class constructor was not officially allowed, even though it was important for, say, validating values being passed to the base class constructor. A popular workaround involved creating static methods to validate values and then calling these methods on the arguments of super() . Though this approach worked well, it could make the code look complicated. This is changing with Statements before super() , a preview language feature in Java 22.

By using this feature, you can opt for a more direct approach, that is, drop the workaround of creating static methods, and execute code that validates arguments, just before calling super() . Terms and conditions still apply, such as, not accessing instance members of a derived class before execution of super() completes.

An example – Validating values passed to super() in a derived class constructor Imagine you need to create a class, say, IndustryElement , that extends class Element , which is defined as follows:

The constructor of the class Element misses checking if the atomicNumber is in the range of 1-118 (all known elements have atomic numbers between 1 to 118). Often the source code of a base class is not accessible or open for modification. How would you validate the values passed to atomicNumber in the constructor of class IndustryElement ?

Until Java 21, no statements were allowed to execute before super() . Here’s one of the ways we developers found a workaround by defining and calling static methods (static methods belong to a class and not to instances and can be executed before any instance of a class exists):

Starting Java 22, you could inline the contents of your static method in the constructor for your derived class, as shown in the following gif:

Here’s the resultant code for your reference:

Where else would you use this feature? If you are new to this feature, I’d recommend that you check out my detailed blog post, Constructor Makeover in Java 22 , in which I’ve covered this feature in detail using the following examples:

Example 2 – base class constructor parameters that use annotations for validations
Example 3 – Transforming variable values received in a derived class constructor, before calling a base class constructor.
Example 4 – Executing statements before this() in constructor of Records
Example 5 – Executing statements before this() in Enum constructors
Example 6 – Executing statements before this() in classes

How does it work behind the scenes? The language syntax has been relaxed but it doesn’t change or impact the internal JVM instructions. There are no changes to the JVM instructions for this new feature because the order of execution of the constructors still remains unchanged – from base class to a derived class. Also, this feature still doesn’t allow you to use members of a derived class instance, until super() executes.

Let’s access and compare the instruction set of the constructor of class IndustryElement , before and after its modification – one that can execute statements before super() and the one that doesn’t. To do so, use the following command:

Here’s the instruction set for the constructor that doesn’t explicitly execute statements before super() and calls static methods to validate range of atomic number:

Here’s instruction set for the constructor that explicitly executes statements before super() to validate range of atomic number:

The most important point to note here is that in both the cases, the constructor of the base class, that is, Element is called, after the execution of all other statements. Essentially, it means, you are still doing the same thing, it is just packaged in a way that makes things easier for you.

I understand it is difficult to remember what each of these instruction codes means. Access the following link and search for the instruction code and following the above instructions set would be a breeze:

https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-6.html#jvms-6.5.aload_n

Can you execute ‘any’ statements before calling super()?

No. If the statements before super() try to access instance variables or execute methods of your derived class, your code won’t compile. For example, if you change the static checkRange() method to an instance method, your code won’t compile, as shown below:

Unnamed Variables and Patterns

Starting Java 22, using Unnamed Variables & Patterns you can mark unused local variables, patterns and pattern variables to be ignored, by replacing their names (or their types and names) with an underscore, that is, _ . Since such variables and patterns no longer have a name, they are referred to as Unnamed variables and patterns. Ignoring unused variables would reduce the time and energy anyone would need to understand a code snippet. In the future, this could prevent errors :-). This language feature doesn’t apply to instance or class variables.

Are you wondering if replacing unused variables with _ is always a good idea, or do they imply code smells and should you consider refactoring your codebase to remove them? Those are good questions to ask. If you are new to this topic, I’d recommend you to check out my detailed blog post: Drop the Baggage: Use ‘_’ for Unnamed Local Variables and Patterns in Java 22 to find out answer to this question.

Since this is not a preview language feature, set Language Level in your Project Settings to ‘22 – Unnamed variables and patterns’ on both the Project and Modules tab, as shown in the below settings screenshot:

A quick example

The following gif gives a sneak peek into how an unused local variable, connection, is detected by IntelliJ IDEA, and could be replaced with an underscore, that is, _ .

The modified code shown in the preceding gif makes it clear that the local variable defined in the try-with-resources statement is unused, making it concise and easier to understand.

Unused Patterns and Pattern variables in switch constructs

Imagine you defined a sealed interface, say, GeometricShape , and records to represent shapes, such as, Point , Line , Triangle , Square , as shown in the following code:

Now assume you need a method that accepts an instance of GeometricShape and returns its area. Since Point and a Line are considered one-dimensional shapes, they wouldn’t have an area. Following is one of the ways to define such method that calculates and returns area:

In the previous example, the patterns int x , int y , Point a and Point B (for case label Line) remain unused as detected by IntelliJ IDEA. These could be replaced by an _ . Also, since all the record components of the case Point remain unused, it could be replaced as Point _ . This could also allow us to merge the first and second case labels. All of these steps are shown in the following gif:

Here’s the modified code for your reference:

In the preceding example, you can’t delete the pattern variables even if they are unused. The code must include the cases when the instance passed to the method calcArea() is of type Point and Line , so that it could return 0 for them.

Unused Patterns or variables with nested records

This feature also comes in quite handy for nested records with multiple unused patterns or pattern variables, as demonstrated using the following example code:

In the preceding code, since the if condition in the method checkFirstNameAndCountryCodeAgain uses only two pattern variables, others could be replaced using _ ; it reduced the noise in the code too.

Where else can you use this feature? Checkout my detailed detailed blog post: Drop the Baggage: Use ‘_’ for Unnamed Local Variables and Patterns in Java 22 to learn more about other use cases where this feature can be used:

Requirements change, but you need side effects of constructs like an enhanced for-loop
Unused parameters in exception handlers; whose signature can’t be modified
Unused auto-closeable resources in try-with-resources statements

It isn’t advisable to use this feature without realising if an unused variable or pattern is a code smell or not. I used these examples to show that at times it might be better to refactor your code to get rid of the unused variable instead of just replacing it with an underscore, that is, _ .

Unused lambda parameter
Methods with multiple responsibilities

Preview Features

‘String Templates’, ‘Implicitly Declared Classes and Instance Main Methods’ and ‘Statements before super()’ are preview language features in Java 22. With Java’s new release cadence of six months, new language features are released as preview features. They may be reintroduced in later Java versions in the second or more preview, with or without changes. Once they are stable enough, they may be added to Java as a standard language feature.

Preview language features are complete but not permanent, which essentially means that these features are ready to be used by developers, although their finer details could change in future Java releases depending on developer feedback. Unlike an API, language features can’t be deprecated in the future. So, if you have feedback about any of the preview language features, feel free to share it on the JDK mailing list (free registration required).

Because of how these features work, IntelliJ IDEA is committed to only supporting preview features for the current JDK. Preview language features can change across Java versions, until they are dropped or added as a standard language feature. Code that uses a preview language feature from an older release of the Java SE Platform might not compile or run on a newer release.

In this blog post, I covered four Java 22 features – String Templates , Implicitly Declared Classes and Instance Main Methods , Statements before super() , and Unnamed variable and patterns .

String Templates is a great addition to Java. Apart from helping developers to work with strings that combine string constants and variables, they provide a layer of security. Custom String templates can be created with ease to accomplish multiple tasks, such as, to decipher letter combinations, either ignoring them or replacing them for added security.

Java language designers are reducing the ceremony that is required to write the first HelloWorld code for Java students, by introducing implicitly declared classes and instance main methods. New students can start with bare minimum main() method, such as, void main() and build strong programming foundation by polishing their skills with basics like sequence, selection and iteration.

In Java 22, the feature Statements before super() lets you execute code before calling super() in your derived class constructors, this() in your records or enums, so that you could validate the method parameters, or transform values, as required. This avoids creating workarounds like creating static methods and makes your code easier to read and understand. This feature doesn’t change how constructors would operate now vs. how they operated earlier – the JVM instructions remain the same.

Unnamed variables are local to a code construct, they don’t have a name, and they are represented by using an underscore, that is, _ . They can’t be passed to methods, or used in expressions. By replacing unused local variables in a code base with _ their intention is conveyed very clearly. It clearly communicates to anyone reading a code snippet that the variable is not used elsewhere. Until now, this intention could only be communicated via comments, which, unfortunately, all developers don’t write.

Happy Coding!

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Java Booleans Explained [Easy Examples]

Introduction to Java booleans

Getting started with Java booleans

Logical operators and Java booleans

Example-1 AND operator and Java booleans

Example-2 OR operator and Java booleans

Example-3 NOT operator and Java booleans

Rational operators and Java booleans

Example-1 Equal and not equal assignment operators and Java booleans

Example-2 Greater than or less than operators and Java booleans

Java booleans in conditional statements