Map

1.Map的主要实现类

2.HashMap的实现原理

3.Map的常用方法

4.遍历Map集合的多种方式

public class MapTest {
    Map map  = new HashMap();
    @Test
    public void test1(){
        map.put(123,"AA");
        map.put(456,"BB");
        map.put("cc",88);

        //获取所有Key
        Set<Object> set = map.keySet();
        Iterator<Object> iterator = set.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }
        System.out.println("========================");
        //获取所有value
        Collection<Object> list = map.values();
        Iterator<Object> iterator1 = list.iterator();
        while (iterator1.hasNext()){
            System.out.println(iterator1.next());
        }
    }

    @Test
    public void test2() {
        map.put(123, "AA");
        map.put(456, "BB");
        map.put("cc", 88);
        //遍历所有键值对 : 方式一
        Set<Object> set = map.entrySet();
        Iterator<Object> iterator = set.iterator();
        while (iterator.hasNext()){
            Object obj = iterator.next();
            Map.Entry entry = (Map.Entry) obj;
            System.out.println(entry.getKey()+"--->"+entry.getValue());
        }
        //遍历所有键值对 : 方式二
        Set set1 = map.keySet();
        Iterator iterator1 = set1.iterator();
        while (iterator1.hasNext()){
            Object key = iterator1.next();
            Object value = map.get(key);
            System.out.println(key+"--->"+value);
        }
        //遍历所有键值对 : 方式三
        for (Object key : map.keySet()) {
            System.out.println(key+"--->"+map.get(key));
        }

    }

}