check positive or negative without using conditional statements in java

Question

An interview question I was asked last week:

I need a function to print out whether a number is positive or negative without using conditional statements like if else while for switch a? b:c etc. How can i do that.

I told the interviewer that it's impossible cuz the question is 'conditional' in nature. He told me it's possible but didn't tell me how. I did quite a bit of search but no good answers.

Answer 1

Just to elaborate on immibis' answer a bit:

int index(int i) {
    return 1 + (i>>31) - (-i>>31);
}

String[] text = {"negative", "zero", "positive"};

private String text(int i) {
    return text[index(i)];
}

The signed shift i>>31 converts every negative number into -1 and every other into 0. Computing -i>>31 allows to tell positive numbers from non-positive ones. Now look at the computed index:

positive: 1 +    0 - (-1) = 2
zero:     1 +    0 -    0 = 1
negative: 1 + (-1) -    0 = 0