Question

How to reverse the bits of a number in Java

Answer 1

public class MyClass {
    private static void print_bits(int n) {
    	System.out.println(String.format("%32s", Integer.toBinaryString(n)).replaceAll(" ", "0"));
    }
    
    private static int reverseBits(int num) {
    	int total_bits = (Integer.SIZE / Byte.SIZE) * 8;
    	int reversed_bits = 0;
    
    	for (int i = 0; i < total_bits; i++) {
    		if ((num & (1 << i)) != 0) {
    			reversed_bits |= 1 << ((total_bits - 1) - i);
    		}
    	}
    
    	return reversed_bits;
    }
    
    public static void main(String args[]) {
	    int num = 42;
	    print_bits(num);
	    num = reverseBits(num);
	    print_bits(num);
	    
	    System.out.println();

	    num = 19;
	    print_bits(num);
	    num = reverseBits(num);
	    print_bits(num);
    }
}






/*
run:
  
00000000000000000000000000101010
01010100000000000000000000000000

00000000000000000000000000010011
11001000000000000000000000000000
  
*/

 

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