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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
  • 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:

Example

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:

Example

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

Try it Yourself »

Or even easier:

Example

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

Try it Yourself »

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

Example

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

Try it Yourself »

Example

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

Try it Yourself »


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:

Example

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

Try it Yourself »

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:

Example

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

Exercise:

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

 isJavaFun = true;
 isFishTasty = false;
System.out.println(isJavaFun);
System.out.println(isFishTasty);

Start the Exercise