Java Concepts Chapter 13: Inheritance

tests whether two references are to the same object

== method

mechanism for extending existing classes by adding methods and fields

Inheritance

in enumeration classes, the toString method returns

a string that equals the objects name

class for which you cannot create obects

abstract class

how do abstract classes differ from interfaces

abstract classes can have instance fields and they can have concrete methods and constructors

protected features can be accessed by

all subclasses and all classes in the same package

The subclass inherits these from the superclass

behavior and state

when you call the clone method you must use a

cast ex. BankAccount clonedAccount = (BankAccount) account.clone();

how to wrtie equals method

cast the otherObject parameter to the type of your class, and then compare the fields of the implicit parameter and the other parameter

makes a new object with the same state as an existing object

clone method

One important reason got inheritance

code reuse

a class which you can create objects for

concrete class

makes it so that no one can extend the class

declaring the class final (you can also declare methods as final so that they can't be overridden)

a type with a finite number of values

enumerated type (enum)

tests whether two objects have the same contents

equals method

Subclasses inherit all

fields from the superclass

testing whether two objects belong to the same class

if (otherObject == null) return false; if (getClass() != otherObject.getClass()) return false;

inheriting methods

if you do not explicitly override a superclass method you automatically inherit it; the superclass methods can be applied to the subclass obects

overriding a method

if you specify a method with the same signature (same name and same parameter types) it overrides the method of the same name in the superclass

failing to invoke the superclass method results in

infinite recursion

sets of classes can form complex

inheritance hierarchies

You can never override

instance fields

must be defined in the subclass

new methods and instance fields

things you can do to methods in a subclass

override, inherit, define new

all methods of classes in the same package can access the feature

package access

the default access when no access modifier is given

package access

can only be accessed by the methods of their own class

private features

a subclass has no access to

private fields of its superclass

four levels of controlling access to fields

public access, private access, protected access, package access

can be accessed by methods of all classes

public features

If you want your toString method to be usable by a subclass

return getClass().getName() + desired print info

Denotes inheritance

solid line with hollow triangle tip

more specialized class that inherits from the superclass

subclass

Any new instance fields that you define in the subclass are present only in

subclass objects

can be converted into superclass references

subclass references

use this keyword to call a method of the superclass

super ex. super.deposit(amount);

more general class that forms the basis for inheritance

superclass

instanceof operator

tests whether an object belongs to a particular type

In Java, every class that does not specifically extend another class extends this

the class Obect

in enumeration classes, the clone method returns

the given object WITHOUT making a copy

If you define a method that does not exist in the superclass then,

the new method can only be applied to subclass obects

method calls are always determined by

the type of the actual object (it doesn't matter if the object reference is stored in a different field type)

calling a superclass constructor

use the super keyword in the first statement of the subclass constructor super(initialBalance)

define the toString method to

yield a string that describes the object state