Which of these pieces of code is faster in Java

问题:

I was wondering which piece of code is going to run faster since I want to optimize as much as possible.

code A:

if(((a & 0x0FFF) + (b & 0x0FFF)) & 0x1000 != 0)
{
    Register.setHCarryFlag(true);
}
else
{
    Register.setHCarryFlag(false);
}

code B:

Register.setHCarryFlag(((a & 0x0FFF) + (b & 0x0FFF))& 0x1000 != 0);

The reason I ask is I suspect that code B doesn't branch, but I don't know for sure how each is converted to machine code.

Better yet, is there a way to see the machine code that is produced from each piece of code?

回答1:

However you turn it, you'll be safer with the second approach because there is fundamentally no branching there, just pure calculation. A good JIT compiler may recognize that your branch in the first example can be eliminated, but why make it more difficult for JIT—and for a human reader.

回答2:

if(__CONDITION_TRUE_?_) 
{
    return true;
} 
else 
{
    return false;
} 

should always be written as

return __CONDITION_TRUE_?_;