STATIC, ABSTRACT, AND INTERFACE

Transcription

1 STATIC, ABSTRACT, AND INTERFACE Thirapon Wongsaardsakul

2 STATIC When variable is a static type, java allocates memory for it at loading time. Class loader Byte code verifier Static variable has been loaded Interpreter Runtime

3 STATIC VALUES CLASS New Object Using Attributes and Methods Object methods and variables Using Attributes and Methods Class methods and variables static

4 YOU CAN REFER TO CIRCLE.PI WITHOUT CREATE A OBJECT BUT NOT FOR A RADIUS class Circle { static double PI = ; double radius = 5; } Golf radius Football radius Volley ball radius CD radius PI =

5 EXERCISE Create Circle and Football Observe static value

6 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++; } }

7 STATIC METHOD public 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 ); } }

8 MAIN METHOD Explain why? public static void main(string[] args) Look at java.lang.math class for static keyword

9 CONSTANT VALUE Keyword final is used to identify a constant variable class Circle { static final double PI = ; double radius = 5; }

10 FINAL CLASS Preventing a user to create subclass public final class Car { } public class SportCar extends Car { } // Wrong

11 ANIMAL KINGDOM Animal Kingdom Mammal Reptile Fish Human Whale Monkey Gold Guppy Fish

12 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

13 ANIMAL KINGDOM Animal Kingdom Mammal Reptile Fish Human Student Whale Monkey Gold Guppy Fish

14 NORMAL CLASS Student is a class if we want it to be

15 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

16 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

17 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

18 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

19 HOW TO USE AN INTERFACE Using 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(); } }

20 EXERCISE Write Airplane.java and Bird.java that implements Flyer interface

21 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

22 EXAMPLE ON INTERFACE

23 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

24 ASSIGNMENT 6 Chapter 5 Programming assignment 4