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<Student> c1= new ArrayList<Student>(); 
		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<Student> c2 = new ArrayList<Student>();
		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<ClassRoom, Collection<Student>> m = new HashMap<ClassRoom,Collection<Student>>();
		m.put(classroom_1, c1);
		m.put(classroom_2, c2);
		
		// 方法 一 ：
		// 转化成  Set<Entry<ClassRoom, Collection<Student>>>，然后在转化为迭代器 
		Iterator<Entry<ClassRoom, Collection<Student>>>  iterator = m.entrySet().iterator();
		
		while(iterator.hasNext()){
			Entry<ClassRoom, Collection<Student>> 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<Student>> 
			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
			*/   
	}
}

java 获取 Map中所有的 key 和 value 值,布布扣,bubuko.com

java 获取 Map中所有的 key 和 value 值