Core Java: Logical Operators

Java provides four logical operators, which operate on boolean operands only, in descending order of precedences, as follows:

Operator	Description	Usage
!	Logical NOT	!booleanExpr
&&	Logical AND	booleanExpr1 && booleanExpr2
||	Logical OR	booleanExpr1 || booleanExpr2

Truth table of logical operator

A	B	A||B	A&&B	!A
False	False	False	False	True
False	True	True	False	True
True	False	True	False	False
True	True	True	True	False

Example:

// Return true if x is between 0 and 100 (inclusive)

(x >= 0) && (x <= 100)

// wrong to use 0 <= x <= 100

 

// Return true if x is outside 0 and 100 (inclusive)

(x < 0) || (x > 100)   //or

!((x >= 0) && (x <= 100))

// Return true if year is a leap year

// A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400.

((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)

Exercise: Study the following program, and explain its output.

/*

 * Test relational and logical operators

 */

public class RelationalLogicalOpTest {

   public static void main(String[] args) {

      int age = 18;

      double weight = 71.23;

      int height = 191;

      boolean married = false;

      boolean attached = false;

      char gender = 'm';

     

      System.out.println(!married && !attached && (gender == 'm'));

      System.out.println(married && (gender == 'f'));

      System.out.println((height >= 180) && (weight >= 65) && (weight <= 80));

      System.out.println((height >= 180) || (weight >= 90));

   }

}