Lecture 14: Objects and Lists

Overview

1. Object Inheritance
2. Representing Lists of Objects

Last Time

• Casting objects as other types
• Class hierarchies
• The Object class
  • every class is a subclass of Object

Why is Object Inheritance Good?

Object has the following methods (among others):

• boolean equals(Object obj)
• String toString()
• …

Therefore, every class in Java has these methods

Testing Methods with Animal

Animal a = new Elephant("Alice");
Animal b = new Elephant("Alice");

What is the behavior of…

• … a.equals(b)?
• … a.toString()?

Let’s see!

Overriding Default Behavior

• default a.equals(b) is equivalent to a == b
• default a.toString() prints address (not meaningful)

How should we…

• … check equality of Animals?
• … represent an Animal as a String?