使用访问者模式或反射的Java动态类转换？(Java dynamic class casting using visitor pattern or reflection? Missing steps or bad implementation?)

 我正在创建基于用户输入具有共同属性的对象，然后将对象传递给将根据对象类型采取适当操作的公共方法。 我已经能够使用访问者类来完成这项工作，但这并不是我想要的。 我希望能够在公共方法中确定对象类型，然后访问与该对象关联的方法。 我不确定我是否接近并且只是遗漏了一些东西，或者我只是执行不好......或两者都是=）。 这是我的（完整）代码： 
 
package com.theory.bang.big;

public interface Particle
{
    public enum ParticleType {
        QUARK,
        LEPTON
}

int processParticle(Particle p);

}


package com.theory.bang.big;

import java.util.ArrayList;
public class Quark implements Particle
{
ArrayList<String> flavorList;

/**
 * Constructor for objects of class Quark
 */
public Quark() 
{
    flavorList = new ArrayList<String>();
    flavorList.add("up");
    flavorList.add("down");
    flavorList.add("charm");
    flavorList.add("strange");
    flavorList.add("top");
    flavorList.add("bottom");
}

public ArrayList<String> getFlavors()
{
    return flavorList;
}


@Override
public int processParticle(Particle p)
{
    System.out.println("In processParticle(Quark)");

    // Never called?

    return 0;
}

}



package com.theory.bang.big;

import java.util.ArrayList;

public class Lepton implements Particle
{
ArrayList<String> typeList;

/**
 * Constructor for objects of class Lepton
 */
public Lepton() 
{   
    typeList = new ArrayList<String>();
    typeList.add("electron");
    typeList.add("electron neutrino");
    typeList.add("muon");
    typeList.add("muon neutrino");
    typeList.add("tau");
    typeList.add("tau neutrino");
}

public ArrayList<String> getTypes()
{
    return typeList;
}

@Override
public int processParticle(Particle p)
{
    System.out.println("In processParticle(Lepton)");

    return 0;
}
}


package com.theory.bang.big;

import java.lang.reflect.*;

class ParticleVisitor
{
public void visit( Quark q )
{
    System.out.println("Quark:[" + q.getFlavors() + "]");
}

public void visit( Lepton l )
{
    System.out.println("Lepton:[" + l.getTypes() + "]");
}

public void visit( Object e ) throws Exception
{
    Method m = getClass().getMethod
     ( "visit", new Class[]{e.getClass()} );
    m.invoke( this, new Object[]{e} );
}
}


package com.theory.bang.big;

import java.io.File;

public class Accelerate implements Particle
{
/**
 * Constructor for objects of class Accelerate
 */
public Accelerate(Particle p)
{
    processParticle(p);
}

//@Override
public int processParticle(Particle p)
{
    try {

        ParticleVisitor pv = new ParticleVisitor();
        pv.visit(p);
    } catch (Exception x) {
        System.out.println(x);
    }

   return 0;
}
}


package com.theory.bang.big;

import java.io.File;
import java.util.Scanner;

public class Physics
{
public static void main(String[] args)
{
   boolean done = false;

   while (!done) {
       System.out.print("Enter the particle [Quark or Lepton]: ");
       Scanner in = new Scanner(System.in);      
       String input = in.next();

       if (input.equals("Quark")) {
           System.out.println("Quark");
           Quark q = new Quark();
           new Accelerate(q);
        } else if (input.equals("Lepton")) {
            System.out.println("Lepton");
            Lepton l = new Lepton();
            new Accelerate(l);
        } else {
            done = true;
        }
    }

}
}
 
 目前我可以通过访问方法打印Quark风格和Lepton类型，但我需要的是能够为Accelerate中的各个对象执行（实现）getter / setter（例如getSpin（），setSpin（double s）） （）。 我错过了什么？ 或者有更好的方法来实现这个？ 
 
 非常感谢您的宝贵时间。 
 
 -Walter 

I am creating objects that will have properties in common based on user input and then passing the objects to a common method that will take appropriate action based on the object type. I've been able to sort of get this working using a visitor class but it is not quite what I want. I want to be able to determine the object type in the common method and then access the methods associated with that object. I am not sure if I am close and just missing something or if I just have a bad implementation... or both =). Here is my (complete) code:
 
package com.theory.bang.big;

public interface Particle
{
    public enum ParticleType {
        QUARK,
        LEPTON
}

int processParticle(Particle p);

}


package com.theory.bang.big;

import java.util.ArrayList;
public class Quark implements Particle
{
ArrayList<String> flavorList;

/**
 * Constructor for objects of class Quark
 */
public Quark() 
{
    flavorList = new ArrayList<String>();
    flavorList.add("up");
    flavorList.add("down");
    flavorList.add("charm");
    flavorList.add("strange");
    flavorList.add("top");
    flavorList.add("bottom");
}

public ArrayList<String> getFlavors()
{
    return flavorList;
}


@Override
public int processParticle(Particle p)
{
    System.out.println("In processParticle(Quark)");

    // Never called?

    return 0;
}

}



package com.theory.bang.big;

import java.util.ArrayList;

public class Lepton implements Particle
{
ArrayList<String> typeList;

/**
 * Constructor for objects of class Lepton
 */
public Lepton() 
{   
    typeList = new ArrayList<String>();
    typeList.add("electron");
    typeList.add("electron neutrino");
    typeList.add("muon");
    typeList.add("muon neutrino");
    typeList.add("tau");
    typeList.add("tau neutrino");
}

public ArrayList<String> getTypes()
{
    return typeList;
}

@Override
public int processParticle(Particle p)
{
    System.out.println("In processParticle(Lepton)");

    return 0;
}
}


package com.theory.bang.big;

import java.lang.reflect.*;

class ParticleVisitor
{
public void visit( Quark q )
{
    System.out.println("Quark:[" + q.getFlavors() + "]");
}

public void visit( Lepton l )
{
    System.out.println("Lepton:[" + l.getTypes() + "]");
}

public void visit( Object e ) throws Exception
{
    Method m = getClass().getMethod
     ( "visit", new Class[]{e.getClass()} );
    m.invoke( this, new Object[]{e} );
}
}


package com.theory.bang.big;

import java.io.File;

public class Accelerate implements Particle
{
/**
 * Constructor for objects of class Accelerate
 */
public Accelerate(Particle p)
{
    processParticle(p);
}

//@Override
public int processParticle(Particle p)
{
    try {

        ParticleVisitor pv = new ParticleVisitor();
        pv.visit(p);
    } catch (Exception x) {
        System.out.println(x);
    }

   return 0;
}
}


package com.theory.bang.big;

import java.io.File;
import java.util.Scanner;

public class Physics
{
public static void main(String[] args)
{
   boolean done = false;

   while (!done) {
       System.out.print("Enter the particle [Quark or Lepton]: ");
       Scanner in = new Scanner(System.in);      
       String input = in.next();

       if (input.equals("Quark")) {
           System.out.println("Quark");
           Quark q = new Quark();
           new Accelerate(q);
        } else if (input.equals("Lepton")) {
            System.out.println("Lepton");
            Lepton l = new Lepton();
            new Accelerate(l);
        } else {
            done = true;
        }
    }

}
}
 
Currently I can print the Quark flavors and Lepton types via the visit methods but what I need is to be able to execute (to be implemented) getter/setters (e.g. getSpin(), setSpin(double s)) for the respective objects in Accelerate(). What am I missing? Or is there a better way to implement this?
 
Thank you very much for your time.
 
-Walter

原文：https://stackoverflow.com/questions/18567202