Experiment 6 inheritance and polymorphism

Experiment six    Inheritance and polymorphism

The experiment purpose

1. Master the use method of interface

2. Master the inheritance of subclasses 、 Subclass object creation process

3. Master the inheritance and hiding of member variables 、 Method inheritance and rewriting

Experimental hours 6 Class hours

Experimental content

1. Write a program for the elderly card of the bus 、 Student card and ordinary citizen card provide charging function . Recharge 、 Charging function extraction , Defined in an interface , Then it is implemented by these three card classes . Finally, write a test class , It is used to test the card swiping operation of bus class III cards .

package code61;

public interface Buscard {  // Defining interfaces Bus card

void recharge();

void charge();

}

package code61;

public class Oldpeople implements Buscard {  // Implementation interface

public void recharge() {

System.out.println(" The elderly card is recharged successfully !");  // Rewrite the recharge method of the interface

}

public void charge() {

System.out.println(" Use a senior citizen card , Deduct one yuan !");  // Rewrite the charging method of the interface

}

}

package code61;

public class People implements Buscard {  // Implementation interface

public void recharge() {

System.out.println(" The ordinary citizen card has been recharged successfully !");  // Rewrite the interface recharge method

}

public void charge() {

System.out.println(" Use an ordinary citizen card , buckle 2 element !");  // Rewrite the interface charging method

}

}

package code61;

public class Student implements Buscard {  // Implementation interface

public void recharge() {

System.out.println(" Student card recharge succeeded !");  // Rewrite the interface recharge method

}

public void charge() {

System.out.println(" Use student cards , buckle 1.5 element !");  // Rewrite the interface charging method

}

}

package code61;

public class Test {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Oldpeople O = new Oldpeople();

O.recharge();

O.charge();  // Define the elderly card object , And call recharge 、 Charging method

Student S = new Student();

S.recharge();

S.charge();  // Define student card object , And call recharge 、 Charging method

People P = new People();

P.recharge();

P.charge();  // Define the citizen card object , And call recharge 、 Charging method

}

}

2. Design four classes 、 An interface , The relationship between classes is as follows ：

 

In the class App Use in Compute、Circle、Rectangle class , stay Compute Class Shape Interface （Shape Object as computeArea The formal parameters of the method ）,Circle、Rectangle Class implementation interface Shape, rewrite area() Method . In the figure “+” It means public,“-” It means private, The upper column in the block diagram is the name of the class or interface , The middle column is the attribute , The next column is the method .

stay App Class main() in ：

1. Create a Compute Class object 、 One Circle Class object and a Rectangle Class object .
2. call Compute Object's computeArea Method ( The actual parameters are Circle object ) Calculate the area of a circle .
3. call Compute Object's computeArea Method ( The actual parameters are Rectangle object ) Calculate rectangular area .

package code62;

public class App {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Compute a = new Compute();

Circle b = new Circle(2);

Rectangle c = new Rectangle(2,2);

System.out.println(" The area of the circle is :"+a.computArea(b));  // call Compute Object's computeArea Method , The argument is Circle object

System.out.println(" The area of the rectangle is :"+a.computArea(c));  // call Compute Object's computeArea Method , The argument is Rectangle object

}

}

package code62;

public class Circle implements Shape {  // Implementation interface

private int radius;

public Circle(int radius) {

this.radius=radius;

}

public double area() {

return PI*radius*radius;  // Rewrite the interface area Method , Find the area of a circle

}

}

package code62;

public class Compute {

public double computArea(Shape s) {  //Shape Object as the formal parameter of the method

return s.area();

}

}

package code62;

public class Rectangle implements Shape {  // Implementation interface

private int width;

private int height;

public Rectangle(int width,int height) {

this.width=width;

this.height=height;

}

public double area() {

return width*height;  // Rewrite the interface area Method , Find the rectangular area

}

}

package code62;

public interface Shape {  // Defining interfaces

double PI=3.14;

double area();

}

3. Ordinary door and alarm door .

（1） Define an interface Alarm（ Call the police ）, Contains an alarm method void alarm( );

（2） Define a class Door（ Ordinary door ）,Door Class has a private property name（ brand ）; Yes 4 Public methods getName、setName、open（ Open door ）、close（ close ）;open、close The function of the method is determined by yourself .

（3） Define a class AlarmDoor（ Alarm door ）, Inherit Door class , Implementation interface Alarm, Override abstract methods in interfaces alarm（ The function of the method is determined by yourself ）.

（3） Write a test class DoorTest, stay main In the method , Give various types of alarm doors and ordinary doors , Call to open the door 、 close 、 Alarm and other actions .

package code63;

public interface Alarm {  // Defining interfaces

void alarm();

}

package code63;

public class AlarmDoor extends Door implements Alarm {  // Inherit Door class , Implementation interface Alarm

public void alarm() {

System.out.println(this.getName()+" Toot toot ! The alarm goes off !");  // Override abstract methods in interfaces

}

}

package code63;

public class Door {

private String name;  // Private property name

public String getName() {  

return name;

}

public void setName(String name) {

this.name=name;

}

public void open() {

System.out.println(this.name+" The door is open !");

}

public void close() {

System.out.println(this.name+" The door is closed !");

}

}

package code63;

public class DoorTest {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

AlarmDoor a1 = new AlarmDoor();

a1.setName(" Low level alarm door !");

a1.open();

a1.alarm();  // Create objects a1, And call each method

AlarmDoor a2 = new AlarmDoor();

a2.setName(" Advanced alarm door !!!");

a2.open();

a2.close();

a2.alarm();  // Create objects a2, And call each method

AlarmDoor a3 = new AlarmDoor();

a3.setName(" Ordinary door .");

a3.open();

a3.close();  // Create objects a3, And call each method

}

}

4.   Design five classes （ Test class 、 Computer class 、 Mobile phones 、 Chargers 、U Disk class ）、 An interface （Usb Interface ）, The relationships between various types are as follows ：

 

（1） stay UsbTest Class main In the method , Create a Xiaomi Mobile object 、 A millet CDQ012M Charger object 、 A Lenovo computer 、 One Kingston U Disk object . Then plug the charger into the mobile phone to charge , take U Insert the disk into the computer .

（2） stay Mobile Class InsertUsb In the method , Connect Usb.

（3） stay Computer Class InsertUsb In the method , Connect Usb.

（4） stay Charger Class connect In the method , Output “ Charger connected , Charging ...”.

（5） stay UDisk Class connect In the method , Output “ Connected U Disc apparatus , Reading data ...”.

package code64;

public class Charger implements Usb {

private String brand;

public Charger(String brand) {

this.brand=brand;

}

public void connect() {

System.out.println(" Charger connected "+this.brand+", Charging ...");  // Rewrite the interface connect Method

}

}

package code64;

public class Computer {

private String brand;

public Computer(String brand) {

this.brand=brand;

}

public void insertUsb(Usb device) {

System.out.println(this.brand);

device.connect();  // Construction connection method

}

}

package code64;

public class Moblie {

private String brand;

public void Moblie(String brand) {

this.brand=brand;

}

public void insertUsb(Usb device) {

System.out.println(this.brand);

device.connect();  // Construction connection method

}

}

package code64;

public class UDisk implements Usb {

private String brand;

public UDisk(String brand) {

this.brand=brand;

}

public void connect() {

System.out.println(" Connected U Disc apparatus "+this.brand+", Reading data ...");  // Rewrite the interface connect Method

}

}

package code64;

public interface Usb {  // Defining interfaces

void connect();

}

package code64;

public class UsbTest {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Moblie a = new Moblie();

a.Moblie("Xiaomi");  // Create a phone object

Charger b = new Charger(" millet CDQ012M");  // Create charger object

Computer c = new Computer(" lenovo ");  // Create computer objects

UDisk d = new UDisk("Kingston");  // establish U Disk object

a.insertUsb(b);  // Plug the charger into the phone

c.insertUsb(d);  //U Insert the disk into the computer

}

}

5. Design a weapon system , Requirements are as follows ：

（1） Define an ammunition class Bullet, There is a ammo name attribute name. Design a construction method and set、get Method .

（2） Define an interface for loading ammunition Loadable, This interface has a loaded abstract method load().

（3） Define an interface that can launch ammunition Launchable, The interface has an abstract method of emission launch().

（4） Define a weapon class Weapon, It can be loaded , It can also be launched .

     Weapons have an attribute name（ Name of weapons ）、 Usable ammunition bullet（Bullet object ） And corresponding get、set Method .

rewrite load Method , Output loaded ammunition in method .

rewrite launch Method , Output the fired ammunition in the method .

（4） Definition 3 Common weapons ：Tank、Flighter、WarShip All inherit weapons Weapon. Every ordinary weapon class has a parameter name Construction method of , Create an ammunition object in the construction method .

tanks Tank The ammunition used is artillery , fighter Flighter The ammunition used is missiles , ships WarShip The ammunition used is torpedo .

（5） Define a class Army, Represents an army , Include ：.

1) attribute ：ArrayList<Weapon> weapon Various weapons used to store military equipment , Find the collection class by yourself ArrayList Usage and generic knowledge points ;

2) How to obtain the number of weapons owned by the army getNum;

3） How to add weapons addWeapon

4) The way to load all weapons with ammunition loadAll;

5） The way to make all weapons attack luanchAll.

（6） Write a test class , stay main In the method ：

1） Build a strong army ;

2） Add various types of weapons , Including tanks 、 aircraft 、 ships .

3） Export the number of weapons owned by the army ;

4） Let all weapons be loaded with ammunition ;

5） Let all weapons be fired .

 

package code65;

import java.util.ArrayList;

public class Army {

ArrayList<Weapon> weapon;

public Army() {

weapon = new ArrayList<Weapon>();  // Store all kinds of weapons for military equipment

}

public int getNum() {

return weapon.size();  // Get the number of weapons the army has

}

public void addWeapon(Weapon weapon) {

this.weapon.add(weapon);  // Add weapons

}

public void loadAll() {

System.out.println(" All weapons are ready to be loaded ...");

int a=1;

for(Weapon weapon:weapon) {

System.out.print(a+":"+weapon.getName());

weapon.load();

a++;  // Let all weapons be loaded with ammunition

}

}

public void luanchAll() {

System.out.println(" All weapons are ready to fight ...");

int a=1;

for(Weapon weapon:weapon) {

System.out.print(a+":"+weapon.getName());

weapon.launch();

a++;  // Let all weapons fire ammunition

}

}

}

package code65;

public class Bullet {

private String name;

public Bullet(String name) {  // Construction method

this.name=name;

}

public void setName(String name) {

this.name=name;

}

public String getName() {

return name;

}

}

package code65;

public class Flighter extends Weapon {  // Inherited weapon class

public Flighter(String name) {

setName(name);

Bullet bullet = new Bullet(" missile ");  // Create missile object

setBullet(bullet);

}

}

package code65;

public interface Launchable {  // Define an interface that can launch ammunition

void launch();

}

package code65;

public interface Loadable {  // Define an interface for loading ammunition

void load();

}

package code65;

public class Tank extends Weapon {  // Inherited weapon class

public Tank(String name) {

setName(name);

Bullet bullet = new Bullet(" The shells ");  // Create shell object

setBullet(bullet);

}

}

package code65;

public class WarShip extends Weapon {  // Inherited weapon class

public WarShip(String name) {

setName(name);

Bullet bullet = new Bullet(" torpedo ");  // Create a torpedo object

setBullet(bullet);

}

}

package code65;

public class Weapon implements Loadable,Launchable {  // Implement two interfaces

private String name;

private Bullet bullet;

public String getName() {

return name;

}

public void setName(String name) {

this.name=name;

}

public Bullet getBullet() {

return bullet;

}

public void setBullet(Bullet bullet) {

this.bullet=bullet;

}

public void load() {

System.out.println(" load "+this.bullet.getName());  // Rewrite the loading method of the interface

}

public void launch() {

System.out.println(" launch "+this.bullet.getName());  // Rewrite the emission method of the interface

}

}

package code65;

public class Test {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Tank a1 = new Tank("99 tanks ");

Flighter a2 = new Flighter(" fighters 20 ");

WarShip a3 = new WarShip(" Wuhan ship ");

WarShip a4 = new WarShip(" Wuhu ship ");

Flighter a5 = new Flighter(" fighters 31 ");

Flighter a6 = new Flighter("F35 ");  // Build an army

Army a = new Army();

a.addWeapon(a1);

a.addWeapon(a2);

a.addWeapon(a3);

a.addWeapon(a4);

a.addWeapon(a5);

a.addWeapon(a6);  // Add all kinds of weapons

System.out.println(" The number of weapons the army is equipped with :"+a.getNum());

a.loadAll();  // Let all weapons be loaded

a.luanchAll();  // Let all weapons fire

}

}

6. Design five classes , The relationship between classes is as follows

 

In the class App Use in Paint、Rectangle、Circle、Rabit class , stay paint Class AsciiArt abstract class （AsciiArt Object as setArt Method parameters ）,Rectangle、Circle、Rabit Class inherits abstract class AsciiArt, And rewrite draw() Method .

Specific design steps ：

1. App Class main( )

1） Create a Paint object paint

2） Show the list of works

======== List of works =======

1. rectangular
2. round
3. Little rabbit

======================

Please select ：

3） According to the choice , Show different works

    ① Draw a rectangular

        a. Create a Rectangle object rect.

b. call paint Of setArt Method , take rect Set to paint Object to display the work .

c. Call object paint Of draw Methods display works .

② A circle

a. Create a Circle object c.

b. call paint Of setArt Method , take c Set to paint Object to display the work .

c. Call object paint Of draw Methods display works .

    ③ Draw a little rabbit

        a. Create a Rabit object rabit.

b. call paint Of setArt Method , take rabit Set to paint Object to display the work .

c. Call object paint Of draw Methods display works .

1. Paint Class draw( )

① Show the name of the work 、 author .

② Calling a member variable art Of draw Methods display works .

1. Rectangle Class draw( )

Output width That's ok height Columns “*”.

1. Circle Class draw( )

For output “*” Composed of circles .

1. Rabit Class draw( )

Output cute rabbit .

package code66;

import java.util.Scanner;

public class App {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Scanner in=new Scanner(System.in);

System.out.println("======== List of works =======");

System.out.println("1. rectangular ");

System.out.println("2. round ");

System.out.println("3. Little rabbit ");

System.out.println("======================");

System.out.println(" Please select :");

int select=in.nextInt();

Paint paint = new Paint();

switch(select){  // According to the choice , Show different works

case 1:

Rectangle rect = new Rectangle(" rectangular "," Zhang San ",3,8);

paint.setArt(rect);  // Calling method , take rect Set to paint Object to display the work

paint.draw();  // call draw Method

break;

case 2:

Circle c = new Circle(" circular "," Smiles send us light ",4);

paint.setArt(c);  // Calling method , take c Set to paint Object to display the work

paint.draw();  // call draw Method

break;

case 3:

Rabit rabit = new Rabit(" The rabbit "," Li Si ");

paint.setArt(rabit);  // Calling method , take rabit Set to paint Object to display the work

paint.draw();   call draw Method

break;

}

}

}

package code66;

public abstract class AssciiArt {  // Define an abstract class

private String title;  // The name of the work

private String author;  // The author's name

public AssciiArt(String title,String author) {

this.title=title;

this.author=author;

}

abstract void draw();  // Abstract drawing method

public String getTitle() {

return title;

}

public void setTitle(String title) {

this.title=title;

}

public String getAuthor() {

return author;

}

public void setAuthor(String author) {

this.author=author;

}

}

package code66;

public class Circle extends AssciiArt {  // Inherit AssciiArt class

private int radius;

public Circle(String title,String author,int radius) {

super(title,author);  // Access the overridden members in the parent class

this.radius=radius;

}

public void draw() {  // Rewrite the drawing method

int d=2*radius;

for(int y=0;y<=d;y++) {

for(int x=0;x<=d;x++) {

if((x-radius)*(x-radius)+(y-radius)*(y-radius)<=radius*radius)

System.out.print("**");

else

System.out.print("  ");

}

System.out.println();  // For output "*" Composed of circles

}

}

}

package code66;

public class Paint {

private AssciiArt art;

public void setArt(AssciiArt art) {  //AsciiArt Object as setArt Method parameters

this.art=art;

}

public void draw() {

System.out.println(" works :"+this.art.getTitle());

System.out.println(" author :"+this.art.getAuthor());

this.art.draw();  // call art Of draw Methods display works

}

}

package code66;

public class Rabit extends AssciiArt {  // Inherit AssciiArt class

public Rabit(String title,String author) {

super(title,author);  // Access the overridden members in the parent class

}

public void draw() {  // Rewrite the drawing method

System.out.println("/)/)");

System.out.println("(- -) )o");

System.out.println("  || ||");  // Draw a little rabbit

}

}

package code66;

public class Rectangle extends AssciiArt {  // Inherit AssciiArt class

private int width;

private int height;

public Rectangle(String title,String author,int width,int height) {

super(title,author);  // Access the overridden members in the parent class

this.width=width;

this.height=height;

}

public void draw() {  // Rewrite the drawing method

for(int a=0;a<width;a++) {

for(int b=0;b<height;b++) {

System.out.print("*");  // Output width That's ok height Columns "*" A rectangle made up of

}

System.out.println();

}

}

}

Summary of experiments

1. Class inheritance is the most effective way to realize code reuse ;
2. Java Only single inheritance is supported , That is, there can only be one parent class , But inheritance between classes can be passed ;
3. Inheritance format ：class Subclass name extends Parent class name ;
4. keyword super It can be used to access the overridden members in the parent class in the subclass ;
5. keyword abstract The decorated class is an abstract class , It is more a parent of other classes , The abstract methods must be implemented in subclasses ;
6. Interface definition format ：【 Modifier 】interface The interface name ;
7. All methods in an interface are abstract , All abstract methods must be overridden in subclasses that implement this interface ;
8. Interface implementation format ：class Class name implements The interface name ;
9. There can be multiple interfaces implemented , Separated by commas ;
10. In addition, we need to master ArrayList How to use .