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
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:
This is useful when we want to compare values to 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
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
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
int myAge = 25; int votingAge = 18; System.out.println(myAge >= votingAge);
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.