1、Student.java
package bo;
public class Student {
private String id ;
public Student(String id){
this.id = id;
}
@Override
public String toString() {
return " 学生：" + id ;
}
}
2、ClassRoom.java
package bo;
public class ClassRoom {
private String id;
public ClassRoom(String id ){
this.id = id;
}
@Override
public String toString() {
return "班级：" + id ;
}
}
3、Test.java
package bo;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class Test {
public static void main(String[] args) {
// 一班
Collection
c1= new ArrayList
(); ClassRoom classroom_1 = new ClassRoom("1班"); Student s1 = new Student("小明"); Student s2 = new Student("小红"); Student s3 = new Student("小光"); c1.add(s1); c1.add(s2); c1.add(s3); // 二班 Collection
c2 = new ArrayList
(); ClassRoom classroom_2 = new ClassRoom("2班"); Student t1 = new Student("小黑"); Student t2 = new Student("小黄"); Student t3 = new Student("小米"); c2.add(t1); c2.add(t2); c2.add(t3); Map
> m = new HashMap
>(); m.put(classroom_1, c1); m.put(classroom_2, c2); // 方法 一 ： // 转化成 Set
>>，然后在转化为迭代器 Iterator
>> iterator = m.entrySet().iterator(); while(iterator.hasNext()){ Entry
> entry = iterator.next(); System.out.println(entry.getKey()); // 获取key, 输出 ClassRoom //System.out.println(entry.getValue()); // 获取value ,输出 Collection
> for(Student s : entry.getValue()){ System.out.println(s); } } System.out.println("==="); // 方法 二 ： Iterator it = m.keySet().iterator(); // Set类型的key值集合，并转换为迭代器 while(it.hasNext()){ ClassRoom key = (ClassRoom) it.next(); // 获取 key 值，ClassRoom System.out.println(key); for(Student s : m.get(key)){ // 获取value 值，Collection (Student) System.out.println(s); } } /* 输出结果： 班级：1班 学生：小明 学生：小红 学生：小光 班级：2班 学生：小黑 学生：小黄 学生：小米 */ } }