STATIC, ABSTRACT, AND INTERFACEtulip.bu.ac.th/~thirapon.w/gim/OOP_files/slide7.pdf · CLASS VS. INTERFACE • Class • Properties and methods deﬁnition • “is-a” relationship:

STATIC, ABSTRACT, AND INTERFACEThirapon Wongsaardsakul

Saturday, August 13, 11

STATIC

• When variable is a static type, java allocates memory for it at loading time.

• Class loader

• Byte code verifier

• Interpreter

• Runtime

Static variable has been loaded


STATIC VALUES

CLASS

Object

New

Using Attributes

and MethodsObject methods and variables

Using Attributes

and MethodsClass methods and variables

static


YOU CAN REFER TO CIRCLE.PI WITHOUT CREATE A OBJECT BUT NOT FOR A RADIUS

class Circle { static double PI = 3.1429; double radius = 5;}

Golfradius

Footballradius

Volleyballradius

PI = 3.1429

CDradius


EXERCISE

• Create Circle and Football

• Observe static value


EXAMPLE (DO IT IN BLUEJ)

\\ Create Student.java

public class Student {

static int numberOfStudent=0;

String name;

public Student(String name) {

this.name = name;

numberOfStudent++;

}

}


STATIC METHODpublic class Student {

static int numberOfStudent=0;

String name;

public Student(String name) {

this.name = name;

numberOfStudent++;

}

public static void printNumberOfStudent() {

System.out.println(“There are “ + numberOfStudent + “ students”);

}

}


MAIN METHOD

• Explain why?

• public static void main(String[] args)

• Look at java.lang.Math class for static keyword


CONSTANT VALUE

• Keyword “final” is used to identify a constant variable

class Circle {

static final double PI = 3.1429;

double radius = 5;

}


FINAL CLASS

• Preventing a user to create subclass

public final class Car { }

public class SportCar extends Car { } // Wrong


ANIMAL KINGDOMAnimal

Kingdom

Mammal Reptile Fish

Human Whale Monkey GuppyGold Fish


ABSTRACT CLASS

• Abstract class is just a definition of something that is not existed in a world

• Mammal, Reptile, and Fish are definition of something

• Human, Whale, Monkey, Gold fish, and Guppy are also definition


ANIMAL KINGDOMAnimal

Kingdom

Mammal Reptile Fish

HumanWhale Monkey GuppyGold

FishStudent


NORMAL CLASS

• Student is a class if we want it to be


EXERCISE

abstract public class Animal {

abstract public void eat();

abstract public void sleep();

} You know that an animal has to eat and sleep But different animals, different eat and sleep

You cannot create object from Animal class

Write class Bird and Person which extends Animal


EXTENDED EXERCISE

abstract public class Animal {

abstract public void eat();

abstract public void sleep();

public void die() {

System.out.println(“I died”);

}

How easy that you can add a functionality all of your classes


INTERFACE CLASS

• Interface is used to apply a rule to a class

• Person class with Swimming interface

• Person class with PayTax interface

• Interface class is a pure abstract class


INTERFACE = PURE ABSTRACT CLASS

• All variables in an interface are “public static final”

• All methods in an interface are “public abstract”

• However, you can ignore all these keywords


HOW TO USE AN INTERFACEUsing keyword “implements” like extends

interface Flyer {

void takeOff();

void land();

void fly();

}

interface Flyer{ abstract public void takeOff(); abstract public void land(); abstract public void fly(); }


EXERCISE

• Write Airplane.java and Bird.java that implements Flyer interface


INHERITANCE AND INTERFACE

• Inheritance and interface are different things

• Inheritance represent “is-a” relationship

• Interface is a rule to apply gain functionalities to a class


EXAMPLE ON INTERFACE


CLASS VS. INTERFACE• Class

• Properties and methods definition

• “is-a” relationship: superclass-subclass

• Details of a method must be completed

• Only have one superclass

• Interface

• Rules definition

• Any classes can have the same interface

• Abstract methods are allowed

• Can implement many interfaces


ASSIGNMENT 6

• Chapter 5

• Programming assignment 4


Documents

STATIC, ABSTRACT, AND INTERFACEtulip.bu.ac.th/~thirapon.w/gim/OOP_files/slide7.pdf · CLASS VS. INTERFACE • Class • Properties and methods deﬁnition • “is-a” relationship: