interface and polymorphism

More later P209 P210

abstract class

you don’t know what it exactly is, it’s usually abstract name, such as animal, canine, feline.

abstract method

abstract class can be concrete in subclass

all abstract methods MUST be implemented by the first concrete subclass down the inheritance tree.

Object

Every class in Java extends class Object.

Object is non-abstract class

some methods are marked final so they can’t be overridden. But some methods are encouraged to be overridden, such as hashCode(), equals(), toString(). more later

equals()

hashCode (now think it as a uni0que ID) see it chapter 17

getClass()

toString() (the result has some numbers you don’t need to care about

Java is a strongly-typed language.

Object o = new Ferrari();

o.goFast();          //Not legal!

The compile knows only

It should be Object d = myDogArrayList.get(0);(Suppose that there are Dogs object in array myDogArrayList)

interface more need to learn

define

public interface Pet{}

implement

public class Dog extends Canine implements Pet{}