关于oop：Java中如何动态创建对象添加到ArrayList中

How to dynamically create Objects to add into ArrayList in Java

我目前正在使用 Java 和 Codename One 构建一个 2D Asteroid 游戏，重点关注 OOP 模式。但是，我在尝试动态创建新对象(在我的情况下，我要添加的对象是超类 GameObject)以添加到 ArrayList 时遇到了麻烦。正如您在 GameWorld.java 的 void init() 方法中看到的那样，我创建了一个包含 GameObject 类型的列表，其中包括 Asteroids、Ships、Spacestations 的子类。

程序要求类中的命令键盘输入，例如\\'a\\'，然后应该将新的Asteroid(GameObject 的子类)对象添加到ArrayList 中。用户应该能够添加任意数量的 Asteroid，以分配给 ArrayList。

我的问题是：在没有像我目前在 GameWorld 类的 addAsteroid() 函数中所做的那样声明 Asteroid 类型的 AsteroidTest 变量的情况下，如何做到这一点？谢谢！

GameWorld.java

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package com.mycompany.a1;

import java.util.ArrayList; //For ArrayList Usage

public class GameWorld {

public void init() {
ArrayList<GameObject> list = new ArrayList<GameObject>();
}
//other methods here to manipulate Game objects and data
public void addShip() {
Ship ShipTest = new Ship();

list.add(ShipTest);

System.out.println(ShipTest.getLocation());
}

public void addAsteroid(){
Asteroid AsteroidTest = new Asteroid();

list.add(AsteroidTest);

System.out.println(AsteroidTest.getLocation());
}

public void addSpaceStation(){

}
}

Game.java

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package com.mycompany.a1;

import com.codename1.ui.events.ActionListener;
import com.codename1.ui.Label;
import com.codename1.ui.TextField;
import com.codename1.ui.events.ActionEvent;
import java.lang.String;
import com.codename1.ui.Form;

public class Game extends Form{
private GameWorld gw;

public Game (){
gw = new GameWorld();
gw.init();
play();

}

private void play(){

Label myLabel=new Label("Enter a Command:"); this.addComponent(myLabel);
final TextField myTextField=new TextField();
this.addComponent(myTextField);
this.show();
myTextField.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evt) {
String sCommand=myTextField.getText().toString();
myTextField.clear();
switch (sCommand.charAt(0)){
case 's':
gw.addShip();
break;
case 'a':
gw.addAsteroid();
break;
case 'b':
gw.addSpaceStation();
break;
//add code to handle rest of the commands
} //switch
} //actionPerformed
} //new ActionListener()
); //addActionListener
} //play
//code to enter text field and receive keyboard input
}

GameObject.java 超类。子类包括小行星、船舶、导弹、空间站

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package com.mycompany.a1;

public abstract class GameObject {
private double x;
private double y;

public GameObject(){
x = 0;
y = 0;
}

public double getX(){
return x;
}

public void setX(double newX){
x = newX;
}

public double getY(){
return y;
}

public void setY(double newY){
y = newY;
}

public String getLocation(){
return"(" + x +"," + y +")";

}
}

Asteroid.java

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package com.mycompany.a1;

import java.util.Random;

public class Asteroid extends MovableObject {

private Random rand = new Random();

public Asteroid() {
setX(rand.nextInt(1023) + rand.nextDouble());

setY(rand.nextInt(767) + rand.nextDouble());// TODO Auto-generated
constructor stub
}

}