Logical Operators

Java provides three logical operators, These are &&(AND), || (OR), and !(NOT)

Logical AND is also called Conditional AND

Logical OR is also called Conditional OR

Logical AND, OR are called Short circuit operators, will see why these are called short circuit soon.

Logical AND Operator

Operand1	Operand2	Evaluates To
TRUE	TRUE	TRUE
TRUE	FALSE	FALSE
FALSE	TRUE	FALSE
FALSE	FALSE	FALSE

As shown in the above table, && operator returns true if both the operands evaluates to true, otherwise returns false.

Example

class AndEx{
 public static void main(String args[]){
  boolean operand1 = true;
  boolean operand2 = true;
  System.out.println((operand1 && operand2)); 

  operand1 = true;
  operand2 = false;
  System.out.println((operand1 && operand2)); 

  operand1 = false;
  operand2 = true;
  System.out.println((operand1 && operand2)); 

  operand1 = false;
  operand2 = false;
  System.out.println((operand1 && operand2));
 }
}

Output

true
false
false
false

Why Logical AND is called short circuit operator

Since if the first statement in the expression evaluates to false, then java won't evaluates the entire expression. So Logical AND is called short circuit AND

Example

class ShortCircuitAnd{
 public static void main(String args[]){
  int a = 10, b=21;
  
  if( (a>b) && (a++ > b) ){
   System.out.println("This statement not evaluated");
  }
  System.out.println("a is not incremented " + a);
  
  if( (a<b) && (a++ < b) ){
   System.out.println("This statement is evaluated");
  } 
  System.out.println("a is not incremented " + a);
  
 }
}

   

Output

a is not incremented 10
This statement is evaluated
a is not incremented 11

Observation

In the expression (a>b) && (a++ > b), a>b is false, so && operator won't evaluates second statement in the expression, so a is not incremented.

Logical OR Operator

Operand1	Operand2	Evaluates To
TRUE	TRUE	TRUE
TRUE	FALSE	TRUE
FALSE	TRUE	TRUE
FALSE	FALSE	FALSE

As shown in the above table, || operator returns true if any of the operand evaluates to true, otherwise returns false.

Example

class OrEx{
 public static void main(String args[]){
  boolean operand1 = true;
  boolean operand2 = true;
  System.out.println((operand1 || operand2)); 

  operand1 = true;
  operand2 = false;
  System.out.println((operand1 || operand2)); 

  operand1 = false;
  operand2 = true;
  System.out.println((operand1 || operand2)); 

  operand1 = false;
  operand2 = false;
  System.out.println((operand1 || operand2));
 }
}

Output

true
true
true
false

Why Logical OR is called short circuit operator

Since if the first statement evaluates to true, then java won't evaluates the entire expression. So Logial OR is called short circuit OR

Example

class ShortCircuitOr{
 public static void main(String args[]){
  int a = 10, b=21;
  
  if( (a<b) || (a++ < b) ){
   System.out.println("This statement evaluated");
  }
  System.out.println("a is not incremented " + a);
  
  if( (a>b) || (a++ > b) ){
   System.out.println("This statement is evaluated");
  } 
  System.out.println("a is incremented " + a);
 }
}

  

Output

This statement evaluated
a is not incremented 10
a is incremented 11

Logical (!)NOT operator

Operand	Evalutes To
FALSE	TRUE
TRUE	FALSE

If the operand is FALSE, ! Operator evaluates it to TRUE

If the operand is TRUE, ! Operator evaluates it to FALSE

Example

class LogicalNot{
 public static void main(String args[]){
  boolean a = true;
  System.out.println((!a));
  
  a = false;
  System.out.println((!a));
 }
}

Output

false
true

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