java Map接口的使用

新建一个学生类，包含的成员变量有学号、姓名以及年龄，然后建立一个测试类，以学号作为键，学生类的对象作为值，保存到Map中，并实现输出，这里主要讲输出访时，核心就是迭代器。

package helloworld;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

public class StudentTest {

	public static void main(String[] args) {
		List<Student> stu = new ArrayList<Student>();
		Student stu1 = new Student("1000", "aaa", 18);
		Student stu2 = new Student("1001", "bbb", 19);
		Student stu3 = new Student("1002", "ccc", 18);
		Student stu4 = new Student("1001", "ddd", 20);
		
		stu.add(stu1);
		stu.add(stu2);
		stu.add(stu3);
		stu.add(stu4);
		
		Iterator<Student> it = stu.iterator();
		while(it.hasNext()){
			System.out.println(it.next());
		}
		Collections.sort(stu, new Comparator<Student>(){

			@Override
			public int compare(Student o1, Student o2) {
				if(o1.id.compareTo(o2.id) == 0){
					return o1.age-o2.age;
				}
				return o1.id.compareTo(o2.id);
			}	
		});
		System.out.println("-----------");	
		Iterator<Student> it1 = stu.iterator();
		while(it1.hasNext()){
			System.out.println(it1.next());
		}
		
	}
}

package helloworld;

import java.util.*;
import java.util.Map.Entry;

public class StudentTest3 {

	public static void main(String[] args) {
		Map<String, Student> map = new HashMap<String, Student>();
		
		Student stu1 = new Student("1000", "aaa", 18);
		Student stu2 = new Student("1001", "bbb", 19);
		Student stu3 = new Student("1002", "ccc", 18);
		Student stu4 = new Student("1003", "ddd", 20);
		
		map.put(stu1.id, stu1);
		map.put(stu2.id, stu2);
		map.put(stu3.id, stu3);
		map.put(stu4.id, stu4);
		
		
		//1\利用键值对
		Set<String> keyset = map.keySet();
		Iterator<String> it = keyset.iterator();
		while(it.hasNext()){
			String nextkey = it.next();
			Student obj = map.get(nextkey);
			System.out.println(nextkey +"--"+obj);
		}
		System.out.println("************");
		//2利用键值对德集合
		Set<Entry<String, Student>> entrySet = map.entrySet();
		Iterator<Entry<String, Student>> it1 = entrySet.iterator();
		while(it1.hasNext()){
			Entry<String, Student> entry = it1.next();
			String id = entry.getKey();
			Student stu = entry.getValue();
			System.out.println(id+"---"+stu);
		}
		System.out.println("************");
		//3
		Collection<Student> col = map.values();
		Iterator<Student> it2 = col.iterator();
		while(it2.hasNext()){
			Student stu0 = it2.next();
			System.out.println("----"+stu0);
		}
	}

}