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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 take the values true or false.


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

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


Boolean Expression

A Boolean expression is a Java expression that returns a Boolean value: true or false.

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

Example

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:

Example

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:

Example

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

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Example

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

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The Boolean value of an expression is the basis for all Java comparisons and conditions.

You will learn more about conditions in the next chapter.