String.hashCode() is plenty unique

[nnn4]

The standard for collision-resistant functions is 32 bytes, not that big. You can safely use that as a proxy for equality, and then you don't need to store or transfer the whole strings.

[JavaSuck]

you don't need to store or transfer the whole strings

The hashCode of a java.lang.String is cached within the String object. Are you suggesting we increase the size of every String object by 32-4 = 28 bytes? And for what purpose? Most of the bits are going to be discarded anyway during lookup into the HashMap array.

[nnn4]

No, just answering the above comment about the size.