Map interface and method

value Time repeatable , But disorderly , use Collection For short . 

Entry: Key value pair object .

        stay Map Class design is , Provides a nested interface （static Modified interface ）：Entry.Entry Encapsulate the correspondence of key value pairs into objects , Key value pair object , So we're walking through Map When the collection , From each key value pair （Entry） Object to get the corresponding key and the corresponding value .

HashMap Implementation principle of JDK7 in

stay JDK8 in ： 

Map Interface method ：

package MapInterface;

import org.junit.Test;

import java.util.*;

/*
map Common methods in interfaces 
 */
public class MapMethod {
    @Test
    public void test1(){
        Map map = new HashMap();
        map.put("aa",123);
        map.put("bb",456);
        map.put("cc",789);
        map.put("dd",101112);
        System.out.println(map);

        Map map1 = new HashMap();

//         modify 
        map1.put("cc",123);
        map1.put("dd",123);

        map.putAll(map1);
        System.out.println(map);

//        remove(Object key)
        Object value = map.remove("cc");
        System.out.println(value);
        System.out.println(map);

//        clear() Empty map Data in , And map=null  Different 
        map.clear();
        System.out.println(map);

    }
//     Element query 
    @Test
    public void test2(){
        Map map = new HashMap();
        map.put("aa",123);
        map.put(123,"aa");
        map.put("bb",456);
//      get(key)
        System.out.println(map.get(123));
//        containisKey(key)
        boolean isExist = map.containsKey("bb");
        System.out.println(isExist);
//        containisValue(value)
        isExist = map.containsValue(123);
        System.out.println(isExist);

        Map map1 = new HashMap();
        map1.put(123,"aa");
        map1.put("aa",123);
        map1.put("bb",456);

        System.out.println(map.equals(map1));
    }

    @Test
    public void test3(){
        Map map = new HashMap();
        map.put(123,1);
        map.put(012,2);
        map.put(456,4);
        System.out.println(map);
    }

    @Test
//    keySet: Traverse key、value、key-value aggregate .
    public void test4(){
        Map map = new HashMap();
        map.put(123,1);
        map.put(012,2);
        map.put(456,4);

//        Traverse key
        Set set = map.keySet();
        Iterator iterator = set.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }

//         Traverse value
        Collection values = map.values();
        for (Object obj : values){
            System.out.println(obj);
        }


//         The way 1：
        Set keyValue = map.entrySet();
        Iterator iterator1 = keyValue.iterator();
        while (iterator1.hasNext()) {
//            Object key = iterator1.next();
//            Map.Entry entry = (Map.Entry)key;
//            System.out.println(entry.getKey()+"===="+entry.getValue());
            System.out.println(iterator1.next());
        }

//         The way 2：
        Set keySet = map.keySet();
        Iterator iterator2 = keySet.iterator();;
        while(iterator2.hasNext()){
            Object key = iterator2.next();
            Object value = map.get(key);
            System.out.println(key+"===="+value);
        }


    }

}