HashMap学习

import java.util.*;

public class UpdateStu {
    public static void main(String[] args) {
        //创建HashMap集合
        Map<String,String> map = new HashMap<>();
        //往集合中添加数据
        map.put("01","小王");
        map.put("02","小李");
        map.put("03","小张");
        map.put("04","小明");
        //判断集合中有没有key"01"的映射
        System.out.println("集合中是否有KEY=01的映射:"+map.containsKey("01"));
        //判断集合中有没有value"小明"的映射
        System.out.println("集合中是否有VALUE=小明的映射:"+map.containsValue("小明"));
        //获取key=02的映射值
        System.out.println("获取key=02的映射值:"+map.get("02"));
        //获取所有的Key集合
        Set<String> set = map.keySet();
        Iterator<String> it = set.iterator();
        System.out.println("集合中所有的Key元素有：");
        while(it.hasNext()){
            System.out.println(it.next());
        }
        //获取所有的Value
        Collection<String> coll = map.values();
        it = coll.iterator();
        System.out.println("集合中所有的Value元素有：");
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}

import java.util.*;

class Emp {
    private String e_id;
    private String e_name;
    public Emp( String e_id,String e_name) {
        this.e_id = e_id;
        this.e_name = e_name;
    }
    public String getE_id() {
        return e_id;
    }
    public void setE_id(String e_id) {
        this.e_id = e_id;
    }
    public String getE_name() {
        return e_name;
    }
    public void setE_name(String e_name) {
        this.e_name = e_name;
    }
}

public class MapText {
    public static void main(String[] args) {
        //创建HashMap集合
        Map<String,String> map = new HashMap<>();
        //创建对象
        Emp emp = new Emp("01", "小王");
        Emp emp2 = new Emp("03", "小张");
        Emp emp3 = new Emp("04", "小明");
        Emp emp4 = new Emp("02", "小李");
        //往集合中加入数据
        map.put(emp.getE_id(), emp.getE_name());
        map.put(emp2.getE_id(), emp2.getE_name());
        map.put(emp3.getE_id(), emp3.getE_name());
        map.put(emp4.getE_id(), emp4.getE_name());
        //获取HashMap对象的key对象集合
        Set<String> set = map.keySet();
        Iterator<String> it = set.iterator();
        System.out.println("HashMap类实现的Map集合，无序：");
        while(it.hasNext()){
            String str = (String)it.next();
            String name = (String)map.get(str);
            System.out.println(str+" "+name);
        }
        //创建TreeMap集合
        TreeMap<String,String> treemap = new TreeMap<>();
        //将HashMap集合中的数据加入到TreeMap中
        treemap.putAll(map);
        //获取TreeMap对象的key对象集合
        Iterator<String> iter = treemap.keySet().iterator();
        System.out.println("TreeMap类实现的Map集合，键对象升序：");
        while(iter.hasNext()){
            String str = (String)iter.next();
            String name = (String)map.get(str);
            System.out.println(str+" "+name);
        }
    }
}