Question

I was browsing through the Java code today and I noticed something.

int[] m = mag;
int len = m.length;
int[] xm = xInt.mag;
if (len != xm.length)
    return false;

(This is in the BigInteger class, which can be found by unzipping src.zip. It’s in the equals method.) Why is an entirely new variable m created when it is only used once? Why isn’t the code just int len = mag.length? I saw this in another method also (bitLength), and again, m is only used once. Is there any advantage to doing this or is it just a mistake by the creators of this class?

Edit: as @usernametbd pointed out, it is used a bit later:

for (int i = 0; i < len; i++)
    if (xm[i] != m[i])
        return false;

But they still could have just used mag. Why would an entirely new variable be made?

In a different function (in the same class, bitLength), a new variable m is made and it’s only used a single time.

Answer 1

Because mag is a field, m is local variable. Access to local variable may be faster, though modern JITs can create such a substitute local variable automatically.

BTW you should have tell what the method you had in mind (I found it to be equals()), and cite original source (it is available) rather than decompiled one.