Question

我试图用Java构建一个简单的Rock-Paper-Scissors游戏。基本上，这个想法是玩家在做出错误行动时会被淘汰出局。剩下的最终球员是胜利者。我相对缺乏经验，不太了解。我运行它时遇到了这个ConcurrentModification异常。我尝试了谷歌，但没有得到任何简单的解决方案。有关像迭代器这样的事情的讨论，我不太了解/理解。

我尝试过如下 -

GameStarter类：

public class GameStarter
{
    public static void main(String[] args)
    {

    RPS g = new RPS();
    g.play();
    }
}

RPS课程：

import java.util.ArrayList;
public class RPS
{
   Player p1 = new Player(" A ");
   Player p2 = new Player(" B ");
   Player p3 = new Player(" C ");
   Player p4 = new Player(" D ");
   Player p5 = new Player(" E ");
   ArrayList<Integer> hold =new ArrayList<Integer>();
   ArrayList<Player> active = new ArrayList<Player>();
   {
    active.add(p1);
    active.add(p2);
    active.add(p3);
    active.add(p4);
    active.add(p5);
        }
   public void play()
   {
    int i,j;
    while(active.size()>1)
    {

     for(Player p:active)
    {
    System.out.print("\n Currently active players are: "+p.name+" , ");
    }   
    System.out.println("\n\n");
    for(Player p:active)
    {
    p.rpsThrow();
    hold.add(p.cur);
    }

    if(hold.contains(1) && hold.contains(2) && !hold.contains(3))
    {
    for(Player p: active)
    {
        if(p.cur==1)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }
    if(hold.contains(1) && !hold.contains(2) && hold.contains(3))
    {
    for(Player p: active)
    {
    if(p.cur==3)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }        
    }

    }
    if(!hold.contains(1) && hold.contains(2) && hold.contains(3))
    {
    for(Player p: active)
    {
        if(p.cur==2)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }

    hold.clear();
    try
    {
    Thread.sleep(3500);
    }
    catch(Exception ex)
    {

    }
}
if(active.size()==1)
{
for(Player p:active)
{
System.out.println("\n\n The winner is : \n"+p.name);
}
}


    }
}

和玩家类：

public class Player
{
  String name;
  Integer cur;

  public Player(String n)
  {
    name=n;
   }
   public int rpsThrow()
   {
    int t;
    t=(int)((Math.random()*3)+1);
    cur=t;
    if(t==1)
    {
        System.out.println("\n"+name+" throws : rock");
    }
    else if(t==2)
    {
        System.out.println("\n"+name+" throws : paper");
    }
    else
    {
        System.out.println("\n"+name+" throws : scissors");
    }
    return t;    
    }
}

有没有简单的方法来解决这个CMException？请随意修改我的代码以解决它。

Answer 1

基本上，一旦你开始在Collection上使用迭代器（并且这种类型的for循环使用迭代器），你就不能修改底层集合，直到完成迭代器，否则你将得到一个CME。如果要从集合中删除项，则需要使用显式迭代器并使用其remove（）方法，如下所示：

public static void main(String[] args) throws Exception {
    List<String> vals = new ArrayList<>();
    vals.add("1"); vals.add("2"); vals.add("3");

    // This throws a CME
    for(String s: vals) {
        if("1".equals(s)) {
            vals.remove(s);
        }
    }

    // This would work
    for(Iterator i = vals.iterator(); i.hasNext(); ) {
        if("1".equals(i.next())) {
            i.remove();
        }
    }
}

Answer 2

我将RPS类更改为此（正常）：

package RockPaperScissors;
import java.util.ArrayList;
public class RPS
{
   Player p1 = new Player(" A ");
   Player p2 = new Player(" B ");
   Player p3 = new Player(" C ");
   Player p4 = new Player(" D ");
   Player p5 = new Player(" E ");
   ArrayList<Integer> hold =new ArrayList<Integer>();
   ArrayList<Player> active = new ArrayList<Player>();
   {
    active.add(p1);
    active.add(p2);
    active.add(p3);
    active.add(p4);
    active.add(p5);
        }
   public void play()
   {
    int i,j;
    Player p;
    while(active.size()>1)
    {

     for(i=0;i<active.size();i++)
    {
      p=  active.get(i);
    System.out.print("\n Currently active players are: "+p.name+" , ");
    }   
    System.out.println("\n\n");
    for(i=0;i<active.size();i++)
    {
      p=  active.get(i);  
    p.rpsThrow();
    hold.add(p.cur);
    }

    if(hold.contains(1) && hold.contains(2) && !hold.contains(3))
    {
    for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
        if(p.cur==1)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }
    if(hold.contains(1) && !hold.contains(2) && hold.contains(3))
    {
    for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
    if(p.cur==3)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }        
    }

    }
    if(!hold.contains(1) && hold.contains(2) && hold.contains(3))
    {
     for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
        if(p.cur==2)
        {
        active.remove(p);
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }

    hold.clear();
    try
    {
    Thread.sleep(3500);
    }
    catch(Exception ex)
    {

    }
}
if(active.size()==1)
{
for(i=0;i<active.size();i++)
{
p=  active.get(i);  
System.out.println("\n\n The winner is : \n"+p.name);
}
}


    }
}

RPE不再存在。虽然我必须说它的表现并不像我期望的那样。我还将尝试研究和研究迭代器。感谢你的帮助。编辑：改变指数与正常。现在它的工作方式就像我想要的那样。

package RockPaperScissors;
import java.util.ArrayList;
public class RPS
{
   Player p1 = new Player(" A ");
   Player p2 = new Player(" B ");
   Player p3 = new Player(" C ");
   Player p4 = new Player(" D ");
   Player p5 = new Player(" E ");
   ArrayList<Integer> hold =new ArrayList<Integer>();
   ArrayList<Player> active = new ArrayList<Player>();
   {
    active.add(p1);
    active.add(p2);
    active.add(p3);
    active.add(p4);
    active.add(p5);
        }
   public void play()
   {
    int i,j;
    Player p;
    while(active.size()>1)
    {

     for(i=0;i<active.size();i++)
    {
      p=  active.get(i);
    System.out.print("\n Currently active players are: "+p.name+" , ");
    }   
    System.out.println("\n\n");
    for(i=0;i<active.size();i++)
    {
      p=  active.get(i);  
    p.rpsThrow();
    hold.add(p.cur);
    }

    if(hold.contains(1) && hold.contains(2) && !hold.contains(3))
    {
    for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
        if(p.cur==1)
        {
        active.remove(p);
        **i=i-1;**
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }
    if(hold.contains(1) && !hold.contains(2) && hold.contains(3))
    {
    for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
    if(p.cur==3)
        {
        active.remove(p);
        i=i-1;
        System.out.println("Player "+p.name+" eliminated ");
        }        
    }

    }
    if(!hold.contains(1) && hold.contains(2) && hold.contains(3))
    {
     for(i=0;i<active.size();i++)
    {
        p=  active.get(i);  
        if(p.cur==2)
        {
        active.remove(p);
        i=i-1;
        System.out.println("Player "+p.name+" eliminated ");
        }
    }

    }

    hold.clear();
    try
    {
    Thread.sleep(3500);
    }
    catch(Exception ex)
    {

    }
}
if(active.size()==1)
{
for(i=0;i<active.size();i++)
{
p=  active.get(i);  
System.out.println("\n\n The winner is : \n"+p.name);
}
}


    }
}

Answer 3

在循环中使用iterator，您可以在其中修改当前迭代的集合

for(Iterator iter = active.iterator(); iter.hasNext();)
{
    Player p = (Player)iter.next();
    if(p.cur==1)
    {
    iter.remove();
    System.out.println("Player "+p.name+" eliminated ");
    }
}

Answer 4

将活动播放器的循环更改为Iterator

Answer 5

这段代码存在问题： -

for(Player p: active)
{
    if(p.cur==2)
    {
    active.remove(p);
    System.out.println("Player "+p.name+" eliminated ");
    }
}

您正在迭代列表活动并从中删除元素。

您需要使用迭代器并从迭代器中删除数据，它将自动从实际列表中删除。

  for(Iterator playerIterator = active.iterator(); playerIterator.hasNext();) {
   Player p = (Player)playerIterator.next();
   if(p.cur==2){
    playerIterator.remove();
   System.out.println("Player "+p.name+" eliminated ");
  }
 }

在这个java游戏中处理ConcurrentModificationException的任何简单方法？

5 个答案: