怪异的移位行为

Question

I was attempting the powerset problem with iteration and bit shifting.
There is a particular behaviour I am unable to comprehend.
I would have expected all the 3 statement below to indicate testing if jth bit in i is set.
Why are the results different then?

private static void printSubsetInBit(Integer[] arr) {
                for(int i=0;i<(1<<arr.length);i++){
                    List<Integer> pack=new ArrayList<Integer>();
                    for(int j=0;j<arr.length;j++){
                        //if(((i>>j)&1)==1){ -->>>> WORKS
                        //if((i & ( 1<<j))>0){-->>>> WORKS
                        if((i & ( 1<<j))==1){ -->>>> DOES NOT WORK
                            pack.add(arr[j]);
                        }
                    }
                    System.out.println(pack.toString());
                }
        }

Answer 1

If you left-shift 1 by j and then use it to mask i, you have to compare the result to the result of left-shifting 1 by j, not to 1.

In other words the condition should be

((i & (1 << j)) == (1 << j))

Or just "!= 0" would be fine.

Answer 2

(i & ( 1<<j))==1 is false unless j == 0 , because ((1<<j) & 1 == 0) == (j != 0) (*).

This is simply not equivalent to the other expressions.

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(*) Well, j % 32 == 0 / j % 32 != 0 ; the second operand is masked.