集合框架（04）HashMap扩展知识

Map扩展知识

map集合被使用是具备映射关系

“bigclass”: “001”, ”zhangsan”

“002”, ”lisi”

“smallclass” : ”001”, “wangwu”

:”002”, “zhaoliu”

一个学校有多个班级，每个班级都有自己的名字

代码示例：

package CollectionTest;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class HashMapDemo4 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        //解决映射中的一对多问题。
        Map<String,String> one = new HashMap<String,String>();
        one.put("001", "zhangsan");
        one.put("002", "lisi");

        Map<String,String> two = new HashMap<String,String>();
        two.put("001", "wangwu");
        two.put("002", "zhaoliu");

        HashMap<String,HashMap<String,String>> school = new HashMap<String,HashMap<String,String>>();
        school.put("bigclass", (HashMap<String, String>) one);
        school.put("smallclass", (HashMap<String, String>) two);

        //遍历school，获取所有班级(通过KeySet方法获得是所有键的String类型)
        Iterator<String> it= school.keySet().iterator();
        while(it.hasNext()){
            String roomName = it.next();
            System.out.println(roomName);
            //通过school的get方法，里面传入的是键，获得one，two
            Map<String,String> room = school.get(roomName);
            getInfo(room);

        }

    }
    public static void getInfo(Map<String,String> roomMap){
        Iterator<String> it = roomMap.keySet().iterator();
        while(it.hasNext()){
            String id = it.next();
            String name = roomMap.get(id);
            System.out.println(id+":"+name);
        }

    }

}

第二种方法：

package CollectionTest;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
class Student3{
    private String id;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    private String name;
    Student3(String id,String name){
        this.id=id;
        this.name=name;
    }
    public String toString(){
        return id+","+name;
    }
}

public class HashMapDemo4 {

    /**
     * @param args
     */
    public static void demo(){
        HashMap<String,List<Student3>> school = new HashMap<String,List<Student3>>();

        List<Student3> big = new ArrayList<Student3>();
        List<Student3> small= new ArrayList<Student3>();
        school.put("big", big);
        school.put("small", small);
        big.add(new Student3("001","zhangsan"));
        big.add(new Student3("002","lisi"));
        small.add(new Student3("001","wangwu"));
        small.add(new Student3("002","zhaoliu"));
        Iterator<String> it = school.keySet().iterator();
        while(it.hasNext()){
            String roomName = it.next();
            List<Student3> stu = school.get(roomName);
            System.out.println(roomName);
            getInfors(stu);

        }

    }
    public static void getInfors(List<Student3> list){
        Iterator<Student3> it2 = list.iterator();
        while(it2.hasNext()){
            Student3 s = it2.next();
            System.out.println(s);
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        demo();
        }
}