Java Logical Operators with Examples

Logical operators are used to performing logical “AND”, “OR” and “NOT” operations, i.e. the function similar to AND gate and OR gate in digital electronics. They are used to combine two or more conditions/constraints or to complement the evaluation of the original condition under particular consideration. One thing to keep in mind is, while using AND operator, the second condition is not evaluated if the first one is false. Whereas while using OR operator, the second condition is not evaluated if the first one is true, i.e. the AND and OR operators have a short-circuiting effect. Used extensively to test for several conditions for making a decision.

1. AND Operator ( && ) – if( a && b ) [if true execute else don’t]
2. OR Operator ( || ) – if( a || b) [if one of them is true execute else don’t]
3. NOT Operator ( ! ) – !(a<b) [returns false if a is smaller than b]

Example For Logical Operator in Java

Here is an example depicting all the operators where the values of variables a, b, and c are kept the same for all the situations.

a = 10, b = 20, c = 30

For AND operator:

Condition 1: c > a                 
Condition 2: c > b         

Output: True [Both Conditions are true]  

For OR Operator:    

Condition 1: c > a 
Condition 2: c > b  

Output: True [One of the Condition if true]

For NOT Operator:
Condition 1: c > a
Condition 2: c > b

Output: False [Because the result was true and NOT operator did it's opposite]

1. Logical ‘AND’ Operator (&&)

This operator returns true when both the conditions under consideration are satisfied or are true. If even one of the two yields false, the operator results false. In Simple terms, cond1 && cond2 returns true when both cond1 and cond2 are true (i.e. non-zero). 

Syntax:

condition1 && condition2

Illustration:

a = 10, b = 20, c = 20

condition1: a < b
condition2: b == c

if(condition1 && condition2)
d = a + b + c

// Since both the conditions are true
d = 50.

Example

Java

// Java code to illustrate
// logical AND operator

import java.io.*;

class Logical {
    public static void main(String[] args)
    {
        // initializing variables
        int a = 10, b = 20, c = 20, d = 0;

        // Displaying a, b, c
        System.out.println("Var1 = " + a);
        System.out.println("Var2 = " + b);
        System.out.println("Var3 = " + c);

        // using logical AND to verify
        // two constraints
        if ((a < b) && (b == c)) {
            d = a + b + c;
            System.out.println("The sum is: " + d);
        }
        else
            System.out.println("False conditions");
    }
}

Output:

Var1 = 10
Var2 = 20
Var3 = 20
The sum is: 50

Now in the below example, we can see the short-circuiting effect. Here when the execution reaches to if statement, the first condition inside the if statement is false and so the second condition is never checked. Thus the ++b(pre-increment of b) never happens and b remains unchanged.

Example:

Java

import java.io.*;

class shortCircuiting {
    public static void main(String[] args)
    {

        // initializing variables
        int a = 10, b = 20, c = 15;

        // displaying b
        System.out.println("Value of b : " + b);

        // Using logical AND
        // Short-Circuiting effect as the first condition is
        // false so the second condition is never reached
        // and so ++b(pre increment) doesn't take place and
        // value of b remains unchanged
        if ((a > c) && (++b > c)) {
            System.out.println("Inside if block");
        }

        // displaying b
        System.out.println("Value of b : " + b);
    }
}

Output:

The output of AND Operator 

2. Logical ‘OR’ Operator (||)

This operator returns true when one of the two conditions under consideration is satisfied or is true. If even one of the two yields true, the operator results true. To make the result false, both the constraints need to return false. 

Syntax:

condition1 || condition2

Example:

a = 10, b = 20, c = 20

condition1: a < b
condition2: b > c

if(condition1 || condition2)
d = a + b + c

// Since one of the condition is true
d = 50.

Java

// Java code to illustrate
// logical OR operator

import java.io.*;

class Logical {
    public static void main(String[] args)
    {
        // initializing variables
        int a = 10, b = 1, c = 10, d = 30;

        // Displaying a, b, c
        System.out.println("Var1 = " + a);
        System.out.println("Var2 = " + b);
        System.out.println("Var3 = " + c);
        System.out.println("Var4 = " + d);

        // using logical OR to verify
        // two constraints
        if (a > b || c == d)
            System.out.println("One or both + the conditions are true");
        else
            System.out.println("Both the + conditions are false");
    }
}

Output

Var1 = 10
Var2 = 1
Var3 = 10
Var4 = 30
One or both + the conditions are true

Now in the below example, we can see the short-circuiting effect for OR operator. Here when the execution reaches to if statement, the first condition inside the if statement is true and so the second condition is never checked. Thus the ++b (pre-increment of b) never happens and b remains unchanged.

Example

Java

import java.io.*;

class ShortCircuitingInOR {
    public static void main (String[] args) {

      // initializing variables
        int a = 10, b = 20, c = 15;

        // displaying b
        System.out.println("Value of b: " +b);

        // Using logical OR
        // Short-circuiting effect as the first condition is true
        // so the second condition is never reached
        // and so ++b (pre-increment) doesn't take place and
        // value of b remains unchanged
        if((a < c) || (++b < c))
            System.out.println("Inside if");

        // displaying b
        System.out.println("Value of b: " +b);

    }
}

Output:

Value of b: 20
Inside if
Value of b: 20

3. Logical ‘NOT’ Operator (!)

Unlike the previous two, this is a unary operator and returns true when the condition under consideration is not satisfied or is a false condition. Basically, if the condition is false, the operation returns true and when the condition is true, the operation returns false. 

Syntax:

!(condition)

Example:

a = 10, b = 20

!(a<b) // returns false
!(a>b) // returns true

Java

// Java code to illustrate
// logical NOT operator
import java.io.*;

class Logical {
    public static void main(String[] args)
    {
        // initializing variables
        int a = 10, b = 1;

        // Displaying a, b, c
        System.out.println("Var1 = " + a);
        System.out.println("Var2 = " + b);

        // Using logical NOT operator
        System.out.println("!(a < b) = " + !(a < b));
        System.out.println("!(a > b) = " + !(a > b));
    }
}

Output:

Var1 = 10
Var2 = 1
!(a < b) = true
!(a > b) = false