Using bitwise & operator and + in Java giving inconsistent results

问题

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);
    }

回答1:

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);.

回答2:

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

num=num+n&1

Will be executed like

num=(num+n)&1

Look here

回答3:

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.

来源：https://stackoverflow.com/questions/13026029/using-bitwise-operator-and-in-java-giving-inconsistent-results