Java布尔方法返回

Question

I have a boolean method in my Java program and I'm wondering why NetBeans is recommending making this change to my code:

return isPrime != 0;

What I wrote was:

if (isPrime == 0) {
            return false;

        }
        else{
            return true;
        }

Both work correctly but I cannot understand the logic behind the change NetBeans is suggesting. Neither true or false is being returned. Could someone explain to me the logic behind this? Thanks

Answer 1

NetBeans is exactly correct. The expression is a boolean. You can easily prove it by making the change and trying it.

What value does 0 != 0 evaluate to? (Hint: it's false ). What about 1 != 0 ? (Hint: it's true ).

Is that not what your more verbose code says?

Answer 2

Instead of

if (isPrime == 0) {
    return false;
} else {
    return true;
}

try

return (isPrime != 0);

It is the same thing, I'll show you the refactoring path. Starting with

if (isPrime == 0) {
    return false;
} else {
    return true;
}

is the same as

if (isPrime != 0) {
    return true;
} else {
    return false;
}

which can be reduced by substitution, substituting 'isPrime != 0' with the function 'doIsPrime()'

private boolean doIsPrime() {
   return isPrime != 0;
}

substituting in

if (doIsPrime()) {
    // guaranteed to be the same as above!
    return doIsPrime();
} else {
    return doIsPrime();
}

which can have both blocks reduced (as duplicated code)

if (doIsPrime()) {
}
return doIsPrime();

And reduced further by removing the if statement around the empty block

return doIsPrime();

Now undo the substitution 'doIsPrime()' back to 'isPrime != 0'

return isPrime != 0;

There was no need to really do the substitution; but, I find it better shows off the reasoning the if statement is redundant.

Answer 3

Neither true or false is being returned.

False. The result of the comparison isPrime != 0 , a boolean is being returned, either true or false .

Could someone explain to me the logic behind this?

The first code is equivalent to the second code. If isPrime is 0 , then return false , else return true . The != operator will yield false if isPrime is 0 , and true if it isn't 0 .

Answer 4

这意味着它返回谓词的结果isPrime != 0如果isPrime = 0，则谓词为false，因此返回false如果isPrime！= 0，则谓词为true，因此返回true

Answer 5

It's just to reduce code.

The expression isPrime != 0 returns a boolean. It is false if isPrime == 0 and true if isPrime != 0 . Thus you can save the if statement and some lines of code.

Answer 6

Just to add to what's already said:

Though your solution and NetBeans recommended approach are exactly correct, one other approach would also be:

if (isPrime == 0) {
    return false;
}

return true;

I don't know what NetBeans would suggest with this approach but I guess that it would propose the same recommendation as it did above.