Bitwise LeftShift and RightShift

[munnanext]

I am learning Bitwise Shift operators, and my question is (Pl see below commented lines in the Program)

Thanks

public class Bitwise {
int i =1;
int j = 1;
public static void main(String args[]) {
Bitwise obj = new Bitwise();
Bitwise obj1 = new Bitwise();
System.out.println(obj.i <<= 31);
//Here I am expecting a value of 2 power 31 but i am getting a negative value
System.out.println(obj.i >>= 31);
//Here I am expecting a value of 1, but I am getting value = -1.
System.out.println(obj.i >>= 1);
//here i am expecting value = 0.5 or 0 since it is integer type but i am getting value of -1.

System.out.println(obj1.j >> 31);
//Here i am expecting a value of 2 power-31 value but i am getting value 0
System.out.println(obj1.j >>= 31);
//Here i am expecting a value of 2 power -62 which is out of range for integer type,but iam getting value of 0.


}

}

 

[prosper]

public class bw {
   int i =1;
   int j = 1;
   int m =-1;
        public static void main(String args[]) {
        bw obj = new bw();
        bw obj1 = new bw();
        System.out.println(obj.i <<= 31);
        // 00000000 00000000 00000000 00000001
        // 00000000 00000000 00000000 00000010
        // 00000000 00000000 00000000 00000100
        // ...
        // 10000000 00000000 00000000 00000000
        //Here I am expecting a value of 2 power 31 but i am getting  a negative value 
        // because the leftest bit became 1. It is negative in 2's complement

        System.out.println(obj.i >>= 31);
        // 10000000 00000000 00000000 00000000 become
        // 11000000 00000000 00000000 00000000 become
        // 11100000 00000000 00000000 00000000 become
        // ...
        // 11111111 11111111 11111111 11111111 (this is negative one in 2's complement)

        // After each right shift, a new bit is added on the leftest bit. A new bit '1' is added to a negative number,
        // a new bit '0' is added to positive number, so right shift will keep negative number maintain negative after right shift
        //Here I am expecting a value of 1, but I am getting value = -1.

        //System.out.println(obj.m >>>= 31);
        //unsigned right shift, A new bit '0' is added to the leftest bit whether positive or negative number

        System.out.println(obj.i >>= 1);
        //here i am expecting  value = 0.5 or 0 since it is integer type but i am getting value of -1.
        
        System.out.println(obj1.j >> 31);
        // 00000000 00000000 00000000 00000001 become
        // 00000000 00000000 00000000 00000000 become
        //   ...
        // 00000000 00000000 00000000 00000000
        // after each right shift, a new bit '0' is added to the leftest bit for right shifting a postive number
        //Here i am expecting a value of 2 power-31 value but i am getting value 0
        System.out.println(obj1.j >>= 31);
        //Here i am expecting a value of 2 power -62 which is out of range for integer type,but iam getting value of 0.
      
      
    }
    
}

 

[chiph]

Here I am expecting a value of 2 power 31 but i am getting a negative value

Java only has signed numbers. It uses the high bit as the sign indicator, so when you set it, your number goes negative.

Chip H.


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