Using bitwise & operator and + in Java giving inconsistent results

Question

Could someone please explain why these two pieces of Java codes are behaving differently? First one correctly counts number of bits but the second one just displays 1 or 0 for non-zero numbers. I don't understand whats happening.

    public static void printNumUnitBits(int n){
    int num=0;
    for(int i=0;i<32;i++){
        int x=n&1;
        num=num+x;
        n=n>>>1;
        }
     System.out.println("Number of one bits:"+num);
    }

    public static void printNumUnitBits(int n){
    int num=0;
    for(int i=0;i<32;i++){
        num=num+n&1;
        n=n>>>1;
        }
     System.out.println("Number of one bits:"+num);
    }

Jeff Bowman · Accepted Answer · 2012-10-23 08:12:15Z

5

In Java, + has higher precedence than &. Your expression num+n&1 will add num and n and then take the lowest bit.

To fix this, try making the statement in the second example num=num+(n&1);.

answered Oct 23, 2012 at 8:12

Jeff Bowman

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Comments

zvez · Accepted Answer · 2012-10-23 08:12:58Z

1

Operator precedence. + has higher priority than &. Your code

num=num+n&1

Will be executed like

num=(num+n)&1

Look here

answered Oct 23, 2012 at 8:12

zvez

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Comments

mdm · Accepted Answer · 2012-10-23 08:14:59Z

1

Operators precedence

int x=n&1;
num=num+x;

and

num=num+n&1;

are different.
You're doing the bitwise & in a different moment.

answered Oct 23, 2012 at 8:14

mdm

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