创建编译时未知的类的实例 [英] Create instance of a class not known at compile time

问题描述

我有一个抽象类:

I have an abstract class:

public abstract class Room {

}

以及在编译时未知的继承类，如:

and inherited classes that are not known at compile time like:

public class MagicRoom extends Room {
	
	public MagicRoom(){
		System.out.println("Creating a MagicRoom.");
	}
	
	public String magic = "";
}

或:

or:

public class Dungeon extends Room {
	
	public Dungeon(){
		System.out.println("Creating a Dungeon");
	}
	
	public String keeper = "";
}

我有一个要从中创建这些类的实例的类:

I have a class that I will be creating instances of these classes from:

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class MazeGame {
	
	public static Room makeRoom(Class roomClass) 
		throws IllegalArgumentException, InstantiationException, 
			IllegalAccessException, InvocationTargetException, 
			SecurityException, NoSuchMethodException{
		
		Constructor c = roomClass.getConstructor();
		return c.newInstance();

	}

}

makeRoom是我尝试创建一个从Room继承的类，该类在编译时不知道，但是我不确定要把什么作为它的返回类型而不是Room.因为makeRoom返回一个Room，所以如果我尝试使用属于继承类的字段，则会得到一个异常:

makeRoom is my attempt to create a class inherited from Room which type I don''t know at compile time, but I''m not sure what to put as its return type instead of Room. Because makeRoom returns a Room I get an exception if I try to use a field that belongs to an inherited class:

import java.lang.reflect.InvocationTargetException;

public class FactoryTest {

	public static void main(String[] args) 
		throws IllegalArgumentException, SecurityException, 
			InstantiationException, IllegalAccessException, 
			InvocationTargetException, NoSuchMethodException{

		MazeGame game = new MazeGame();
		
		Room magicRoom = MazeGame.makeRoom(MagicRoom.class);
		
		/*
		 * Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
		 * magic cannot be resolved or is not a field
		 */
		
		magicRoom.magic = "a"; 

	}
}

在此先感谢.

Thanks in advance.

推荐答案

我需要使该方法通用，在此处获得关于StackOverflow的答案:

解决方案 [

I needed to make the method generic, got the answer on StackOverflow here:

the solution[^]

For reference, here is the code:

public static  T makeRoom(Class roomClass) 
    throws IllegalArgumentException, InstantiationException, 
        IllegalAccessException, InvocationTargetException, 
        SecurityException, NoSuchMethodException{

    // This is enough, if you have 0-arg constructor in all your subclasses
    return roomClass.newInstance();
}

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