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.
The name boolean comes from George Boole , a mathematician who first defined the logic system used in computers today.
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 falseIn practice, booleans are most often the result of expressions, and are used to test conditions in programs (see below).
Boolean Expressions
A boolean expression returns a boolean value: true or false .
This is useful to build logic and make decisions in programs.
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); // Outputs true, because 10 is greater than 9Example
System.out.println(10 > 9); // Outputs true, because 10 is greater than 9Or even easier
In the examples below, we use the equal to ( == ) operator to evaluate an expression:
Example
int x = 10;
System.out.println(x == 10); // Outputs true, because the value of x is equal to 10Example
System.out.println(10 == 15); // Outputs false, because 10 is not equal to 15Store the Result in a Boolean Variable
You can also store the result of a comparison in a boolean variable:
Example
int x = 10;
int y = 9;
boolean isGreater = x > y;
System.out.println(isGreater); // Outputs trueNote
It is up to you whether you store the result of a comparison in a boolean variable or use the comparison directly. Storing the result can make your code easier to read, especially if you want to reuse it.