java - Why define object for getEntry in HashMap

Question

I am new to generics and I am not sure if the answer to my question is opinion based or has a genuine reason. In the following code what was need to case a key of an entry to an object ?

Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))

It appears to be easily replaced by

if (e.hash == hash && (e.key == key || (key != null && key.equals(e.key))))

More reference:

 final Entry<K,V> getEntry(Object key) {
        int hash = (key == null) ? 0 : hash(key);
        for (Entry<K,V> e = table[indexFor(hash, table.length)];
             e != null;
             e = e.next) {
            Object k;
            if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                return e;
        }
        return null;
    }

Answer 1

This is an extreme optimization measure that is probably not necessary for general purpose programming practice. Here is a discussion that could answer your question. Below statement is copied from that post:

It's a coding style made popular by Doug Lea. It's an extreme optimization that probably isn't necessary; you can expect the JIT to make the same optimizations. (you can try to check the machine code yourself!) Nevertheless, copying to locals produces the smallest bytecode, and for low-level code it's nice to write code that's a little closer to the machine.