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 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 y = 9;
System.out.println(x > y); // returns true, because 10 is higher than 9
Or even easier:
In the examples below, we use the equal to (
==) operator to evaluate an expression:
System.out.println(x == 10); // returns true, because the value of x is equal to 10
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.