Java两个乒乓球队比赛名单问题(判断素数)

import java.util.ArrayList;public class pingpang {  String a,b,c;  public static void main(String[] args) {  String[] op = { "x", "y", "z" };  ArrayList<pingpang> arrayList=new ArrayList<pingpang>();  for (int i = 0; i < 3; i++)  for (int j = 0; j < 3; j++)  for (int k = 0; k < 3; k++) {  pingpang a=new pingpang(op[i],op[j],op[k]);   if(!a.a.equals(a.b)&&!a.b.equals(a.c)&&!a.a.equals("x")   &&!a.c.equals("x")&&!a.c.equals("z")){   arrayList.add(a);   }  }  for(Object a:arrayList){  System.out.println(a);  }  }  public pingpang(String a, String b, String c) {  super();  this.a = a;  this.b = b;  this.c = c;  }  @Override  public String toString() {  // TODO Auto-generated method stub  return "a的对手是"+a+","+"b的对手是"+b+","+"c的对手是"+c+"/n";  }}