import java.util.*;
import java.lang.*;

public class PolMsg {     
Police pol1 = new Police(23,"zhang1");
Police pol2 = new Police(24,"zhang2");
Police pol3 = new Police(24,"zhang3");
Police pol4 = new Police(24,"zhang4");
Police pol5 = new Police(24,"zhang5");
public void addPol3(){
  try{
   HashMap<Integer,Police> col1 = new HashMap<Integer,Police>();
   col1.put(new Integer(1),pol1);
   col1.put(new Integer(2),pol2);
   col1.put(new Integer(3),pol3);
   col1.put(new Integer(4),pol4);
   col1.put(new Integer(5),pol5);
   for(Iterator i = col1.keySet().iterator();i.hasNext();){
    Police col = (Police) i.next();
    System.out.println(col.getName()+col.getAge());
   }
   System.out.println();
  }catch(ClassCastException e){
   e.printStackTrace();
  }
  
}

public static void main(String[] args) {
  PolMsg p1 = new PolMsg();
  //p1.addPol1();
  //p1.addPol2();
  p1.addPol3();
}
}
请问为什么会抛异常呢？望赐教

这句Iterator i = col1.keySet().iterator()，得到的遍历对象是 Integer的，无法得到police对象。

应该这样：

1. for(Iterator i = col1.keySet().iterator();i.hasNext();){
   
2.                    Integer x = (Integer) i.next();
   
3.                    System.out.println(col1.get(x).getName()+col1.get(x).getAge());
   
4.            }

复制代码

先得到键，再通过map得到值，再由值获得属性。

import java.util.*;

public class PolMsg {     
public static void main(String[] args) {
    PolMsg p1 = new PolMsg();
    // p1.addPol1();
    // p1.addPol2();
    p1.addPol3();
  }
Police pol1 = new Police(23,"zhang1");
Police pol2 = new Police(24,"zhang2");
Police pol3 = new Police(24,"zhang3");
Police pol4 = new Police(24,"zhang4");
Police pol5 = new Police(24,"zhang5");

public void addPol3(){
   try{
    HashMap<Integer,Police> col1 = new HashMap<Integer,Police>();
    col1.put(new Integer(1),pol1);
    col1.put(new Integer(2),pol2);
    col1.put(new Integer(3),pol3);
    col1.put(new Integer(4),pol4);
    col1.put(new Integer(5),pol5);
    for(Iterator<Integer> i = col1.keySet().iterator();i.hasNext();){
     Integer key = i.next();    //红色标注为代码的改动，你的代码这个地方会抛格式转化异常
     Police col = col1.get(key);
     System.out.println(col.getName()+"   "+col.getAge());
    }
    System.out.println();
   }catch(ClassCastException e){
    e.printStackTrace();
   }
   
}
}
class Police{
private int age;
private String name;
public Police(int age, String name) {
  super();
  this.age = age;
  this.name = name;
}
public int getAge() {
  return age;
}
public void setAge(int age) {
  this.age = age;
}
public String getName() {
  return name;
}
public void setName(String name) {
  this.name = name;
}

}
运行结果如下：