Java Collections

Pre condition, post condition and Invariants

1. Pre-conditions are the things that must be true before a method is called.The method tells clients "this is what I expect from you".
2. Post-conditions are the things that must be true after the method is complete. The method tells clients "this is what I promise to do for you".
3. Invariants are the things that are always true and won't change. The method tells clients "if this was true before you called me, I promise it'll still be true when I'm done".