The first day of start learning Thinking in java

1 In  a good object-oriented design, each object dose one thing well, but doesn't try to do too much.

2 Code reuse is one of  the greatest advantages that object-oriented programming languages provide.

3 To override a method,you simply create a new definition for the method in the derived class.You are saying,"I'm using the same interface method here, but i want to do something different for my new type."

4 A test for inheritance is to determine whether you can state the is-a relationship about the classes and have it make sense.