What are the differences between == and equals?

As a reminder, it needs to be said that generally, == is NOT a viable alternative to equals. When it is, however (such as with enum), there are two important differences to consider:

1. == never throws NullPointerException

enum Color { BLACK, WHITE };

Color nothing = null;
if (nothing == Color.BLACK);      // runs fine
if (nothing.equals(Color.BLACK)); // throws NullPointerEx

2. == is subject to type compatibility check at compile time

enum Color { BLACK, WHITE };
enum Chiral { LEFT, RIGHT };

if (Color.BLACK.equals(Chiral.LEFT)); // compiles fine
if (Color.BLACK == Chiral.LEFT);      // DOESN'T COMPILE!!! Incompatible types!