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
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?
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.
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.
It means its returning the result of the predicat isPrime != 0
If isPrime = 0, then the predicat is false, therefore it return false
If isPrime != 0, then the predicat is true, therefore returning true
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.
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.