Java Booleans

In programming, there are often scenarios where you need a data type that can only have one of two values, such as:

• YES / NO
• ON / OFF
• TRUE / FALSE

Java provides the boolean data type to store such true or false values.

Boolean Values

A boolean type is declared using the boolean keyword and can only take the values true or false:

// Example
boolean isCarFast = true;
boolean isMotorcycleQuiet = false;
System.out.println(isCarFast);     // Outputs true
System.out.println(isMotorcycleQuiet); // Outputs false

// Example

boolean isCarFast = true;

boolean isMotorcycleQuiet = false;

System.out.println(isCarFast);     // Outputs true

System.out.println(isMotorcycleQuiet); // Outputs false

However, it’s more common to return boolean values from boolean expressions for conditional testing.

Boolean Expression

A boolean expression evaluates to a boolean value: true or false. This is useful for building logic and finding answers.

For example, you can use a comparison operator, such as the greater than (>) operator, to determine if an expression (or variable) is true or false:

// Example
int speedCar = 120;
int speedBike = 100;
System.out.println(speedCar > speedBike); // returns true, because 120 is greater than 100

// Example

int speedCar = 120;

int speedBike = 100;

System.out.println(speedCar > speedBike); // returns true, because 120 is greater than 100

Or even more simply:

// Example
System.out.println(150 > 100); // returns true, because 150 is greater than 100

// Example

System.out.println(150 > 100); // returns true, because 150 is greater than 100

In the examples below, we use the equal to (==) operator to evaluate an expression:

// Example
int topSpeed = 200;
System.out.println(topSpeed == 200); // returns true, because the value of topSpeed is equal to 200

// Example
System.out.println(150 == 100); // returns false, because 150 is not equal to 100

// Example

int topSpeed = 200;

System.out.println(topSpeed == 200); // returns true, because the value of topSpeed is equal to 200

​

// Example

System.out.println(150 == 100); // returns false, because 150 is not equal to 100

Real Life Example

Let’s consider a “real life example” where we need to determine if a vehicle’s speed exceeds the legal speed limit.

In the example below, we use the >= comparison operator to check if the speed (75) is greater than or equal to the speed limit, which is set to 60:

// Example
int vehicleSpeed = 75;
int speedLimit = 60;
System.out.println(vehicleSpeed >= speedLimit); // returns true

// Example

int vehicleSpeed = 75;

int speedLimit = 60;

System.out.println(vehicleSpeed >= speedLimit); // returns true

An even better approach would be to wrap the code above in an if…else statement, so we can perform different actions depending on the result:

// Example
int vehicleSpeed = 75;
int speedLimit = 60;

if (vehicleSpeed >= speedLimit) {
  System.out.println("Over the speed limit!");
} else {
  System.out.println("Within the speed limit.");
}

// Example

int vehicleSpeed = 75;

int speedLimit = 60;

​

if (vehicleSpeed >= speedLimit) {

  System.out.println("Over the speed limit!");

} else {

  System.out.println("Within the speed limit.");

}