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Java Booleans

Java Booleans

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

  • YES / NO
  • ON / OFF

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:


boolean isJavaFun = true;
boolean isFishTasty = false;
System.out.println(isJavaFun);     // Outputs true
System.out.println(isFishTasty);   // Outputs 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:


int x = 10;
int y = 9;
System.out.println(x > y); // returns true, because 10 is higher than 9

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Or even easier:


System.out.println(10 > 9); // returns true, because 10 is higher than 9

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


int x = 10;
System.out.println(x == 10); // returns true, because the value of x is equal to 10

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System.out.println(10 == 15); // returns false, because 10 is not equal to 15

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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:


int myAge = 25;
int votingAge = 18;
System.out.println(myAge >= votingAge);

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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.":

int myAge = 25;
int votingAge = 18;

if (myAge >= votingAge) {
  System.out.println("Old enough to vote!");
} else {
  System.out.println("Not old enough to vote.");

Try it Yourself »

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:

 isJavaFun = true;
 isFishTasty = false;

Start the Exercise