一个集合的题目，我第四问不会做，求帮忙啊！

import java.util.*;
public class Xipai {
   

    /**
     * 用于输出显示
     * @param name
     * @param list
     */
    public static void display(String name,List<Pai> list){
        StringBuilder sb=new StringBuilder();
        sb.append(name).append(":");
        Iterator<Pai> iter=list.iterator();
        while(iter.hasNext()){
            sb.append(iter.next().toString());
            if(iter.hasNext()){
                sb.append(",");
            }
        }
        System.out.println(sb.toString());
    }
   

    /**
     * @param args
     */
    public static void main(String[] args) {
        //（1）对一副扑克牌洗牌。（2）按照红桃，黑桃，梅花，方块排序。
        //（3）按照2或4人分牌，并显示每人的牌。（4）查询是否有一对牌以及他在牌中的位置。
        System.out.println("=========生成牌==============");
        List<Pai> list=Pai.create();
        display("显示：", list);
        System.out.println("=========洗牌==============");
        Collections.shuffle(list);
        display("显示：", list);
        System.out.println("=========按花色排序==============");
        Collections.sort(list, new Comparator<Pai>() {

            @Override
            public int compare(Pai o1, Pai o2) {
                int x=(o1.getHuase()+1)*50+(o1.getShuzhi()+1);
                int y=(o2.getHuase()+1)*50+(o2.getShuzhi()+1);
                return x-y;
            }
           

        });
        display("显示：", list);
        System.out.println("=========洗牌并发牌==============");
        Collections.shuffle(list);
        List<Pai> list1=list.subList(0, 2*13);
        List<Pai> list2=list.subList(2*13, 4*13);
        display("甲：", list1);
        display("乙：", list2);
        System.out.println("=========找牌==============");
        List<Pai> list3=new ArrayList<Pai>(list1);
        List<Pai> list4=new ArrayList<Pai>(list2);
        Comparator<Pai> com=new Comparator<Pai>() {
            @Override
            public int compare(Pai o1, Pai o2) {
                int x=o1.getShuzhi();
                int y=o2.getShuzhi();
                return x-y;
            }
        };
        Collections.sort(list3, com);
        Collections.sort(list4, com);
        Stack<Pai> stack=new Stack<Pai>();
        System.out.println("=========甲==========");
        for (Pai pai : list3) {
            if(stack.empty()){
                stack.push(pai);
            }else if(stack.peek().getShuzhi().equals(pai.getShuzhi())){
                stack.push(pai);
            }else{
                if(stack.size()==2){
                    Pai p1=stack.pop();
                    Pai p2=stack.pop();
                    System.out.println("一对："+p1.showShuzhi()+"  位置：第"+(list1.indexOf(p1)+1)+"张,第"+(list1.indexOf(p2)+1)+"张");
                }
                stack.clear();
                stack.push(pai);
            }
        }
        if(stack.size()==2){
            Pai p1=stack.pop();
            Pai p2=stack.pop();
            System.out.println("一对："+p1.showShuzhi()+"  位置：第"+(list1.indexOf(p1)+1)+"张,第"+(list1.indexOf(p2)+1)+"张");
        }
        System.out.println("=========乙==========");
        stack.clear();
        for (Pai pai : list4) {
            if(stack.empty()){
                stack.push(pai);
            }else if(stack.peek().getShuzhi().equals(pai.getShuzhi())){
                stack.push(pai);
            }else{
                if(stack.size()==2){
                    Pai p1=stack.pop();
                    Pai p2=stack.pop();
                    System.out.println("一对："+p1.showShuzhi()+"  位置：第"+(list2.indexOf(p1)+1)+"张,第"+(list2.indexOf(p2)+1)+"张");
                }
                stack.clear();
                stack.push(pai);
            }
        }
        if(stack.size()==2){
            Pai p1=stack.pop();
            Pai p2=stack.pop();
            System.out.println("一对："+p1.showShuzhi()+"  位置：第"+(list2.indexOf(p1)+1)+"张,第"+(list2.indexOf(p2)+1)+"张");
        }
        stack.clear();
    }
}

class Pai{
    private static String[] paiList = new String[] { "2", "3", "4", "5", "6", "7", "8",
            "9", "10", "J", "Q", "K", "A" };
    private static String[] huaselist = new String[] { "红桃", "黑桃", "梅花", "方块" };
    private Integer huase;
    private Integer shuzhi;
   

    /**
     * 创建4*13张牌
     * @return
     */
    public static List<Pai> create(){
        List<Pai> list=new ArrayList<Pai>(4*13);
        for (int i = 0; i < paiList.length; i++) {
            for (int j = 0; j < huaselist.length; j++) {
                list.add(new Pai(j, i));
            }
        }
        return list;
    }
   

    public String showShuzhi() {
        return paiList[shuzhi];
    }

    public Integer getHuase() {
        return huase;
    }
    public void setHuase(Integer huase) {
        this.huase = huase;
    }
    public Integer getShuzhi() {
        return shuzhi;
    }
    public void setShuzhi(Integer shuzhi) {
        this.shuzhi = shuzhi;
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((huase == null) ? 0 : huase.hashCode());
        result = prime * result + ((shuzhi == null) ? 0 : shuzhi.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Pai other = (Pai) obj;
        if (huase == null) {
            if (other.huase != null)
                return false;
        } else if (!huase.equals(other.huase))
            return false;
        if (shuzhi == null) {
            if (other.shuzhi != null)
                return false;
        } else if (!shuzhi.equals(other.shuzhi))
            return false;
        return true;
    }
    public Pai(Integer huase, Integer shuzhi) {
        super();
        this.huase = huase;
        this.shuzhi = shuzhi;
    }
    @Override
    public String toString() {
        return huaselist[huase]+" "+paiList[shuzhi]+" ";
    }
   

   

}