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
A boolean type is declared with the
boolean keyword and can only take the values
boolean isJavaFun = true; boolean isFishTasty = false; System.out.println(isJavaFun); // Outputs true System.out.println(isFishTasty); // Outputs false
However, it is more common to return boolean values from boolean expressions, for conditional testing (see below).
A Boolean expression is a Java expression that returns a Boolean value:
You can use a comparison operator, such as the greater than (
>) operator to find out if an expression (or a variable) is true:
int x = 10; int y = 9; System.out.println(x > y); // returns true, because 10 is higher than 9
Or even easier:
System.out.println(10 > 9); // returns true, because 10 is higher than 9
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
System.out.println(10 == 15); // returns false, because 10 is not equal to 15
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.