A Boolean expression is a Java expression that returns a Boolean value: true or false . 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 true or false.
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 false
However, it is more common to return boolean values from boolean expressions, for conditional testing (see below).
Boolean Expression
A Boolean expression is a Java expression that returns a Boolean value: true or false. You can use a comparison operator, such as the greater than (>) operator to find out if an expression (or a variable) is true:
Example
int x = 10; int y = 9; System.out.println(x > y); // returns true, because 10 is higher than 9
Or even easier:
Example
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:
Example
int x = 10; System.out.println(x == 10); // returns true, because the value of x is equal to 10
Example
System.out.println(10 == 15); // returns false, because 10 is not equal to 15
How do you add a Boolean in Java?
To display Boolean type, firstly take two variables and declare them as boolean. val1 = true; Now, use if statement to check and display the Boolean true value. if(val1) System.
Examples of Java boolean keyword
Example 1: Simple boolean example
public class BooleanExample1 {
public static void main(String[] args) {
int num1=10;
int num2=20;
boolean b1=true;
boolean b2=false;
if(num1<num2)
{
System.out.println(b1);
}
else
{
System.out.println(b2);
}
}
} Output:
true
Example 2: Comparing the variables of boolean type
public class BooleanExample2 {
public static void main(String[] args) {
boolean b1=true;
boolean b2=false;
boolean b3=(b1==b2);
System.out.println(b1);
System.out.println(b2);
System.out.println(b3);
}
} Output:
true
false
false
Example 3: Method of boolean type
public class BooleanExample3 {
public static boolean display(int num)
{
if(num>10)
{
return true;
}
else
{
return false;
}
}
public static void main(String[] args) {
System.out.println(display(15));
}
} Output:
true
Example 4: Comparing objects
public class BooleanExample4 {
public static void main(String[] args) {
BooleanExample4 b1=new BooleanExample4();
BooleanExample4 b2=new BooleanExample4();
boolean result=(b1==b2);
System.out.println("Is objects are equal : "+result);
}
Output:
Is objects are equal : false
Example 5: Finding a prime number
public class BooleanExample5 {
public static void main(String[] args) {
int num=7;
boolean flag=false;
for(int i=2;i<num;i++)
{
if(num%i==0)
{
flag=true;
break;
}
}
if(flag)
{
System.out.println("Not prime");
}
else
{
System.out.println("prime");
}
}
} Output:
prime
