Map常用的子类：

1. |---Hashtable：内部结构是哈希表，是同步的，不允许null作为键，null作为值
   |--Properties：用来存储键值对型的配置文件的信息。可以和IO技术相结合。
2. |---HashMap：内部结构是哈希表，不是同步的，允许null作为键，null作为值。
3. |---TreeMap：内部结构是二叉树，不是同步的，可以对Map集合中的键进行排序
   HashMap存储自定义对象：
   将学生对象和学生归属地通过键与值存储到map集合中。

HashMap

package com.vv.map.demo;

import java.io.ObjectInputStream.GetField;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;

import com.vv.bean.Student;

public class HashMapDemo {

    public static void main(String[] args) {

        HashMap<Student,String> map = new HashMap<Student,String>();
        map.put(new Student("zhangsan",12),"上海");
        map.put(new Student("lisi",22),"北京");
        map.put(new Student("zhangsan",12),"天津");
        map.put(new Student("zhaoliu",12),"成都");

        Set<Student> set = map.keySet();
        Iterator<Student> it = set.iterator();
        while(it.hasNext()){
            Student key = it.next();
            String value = map.get(key);
            System.out.println( key.getAge()+ ":" + key.getName() + ":" + value);
        }
    }

}

TreeMap

package com.vv.map.demo;

import java.nio.MappedByteBuffer;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

import com.vv.bean.Student;
import com.vv.comparator.ComparatorByName;

public class TreeSetMap {

    public static void main(String[] args) {
        TreeMap<Student,String> ts = new TreeMap<Student,String>(new ComparatorByName());
        ts.put(new Student("zhangsan",12),"上海");
        ts.put(new Student("lisi",22),"北京");
        ts.put(new Student("zhangsan",12),"天津");
        ts.put(new Student("zhaoliu",12),"成都");

        Set<Map.Entry<Student, String>> set = ts.entrySet();
        Iterator<Map.Entry<Student, String>> it = set.iterator();
        while(it.hasNext()){
            Map.Entry<Student, String> map = it.next();
            Student key = map.getKey();
            String value = map.getValue();
            System.out.println( key.getAge()+ ":" + key.getName() + ":" + value);
        }

    }

}