Java Map接口及其实现类原理解析

int size();//获取Map集合大小(即元素数量)
boolean isEmpty();//判断是否为空
boolean containsKey(Object key);//判断是否包含某个键
boolean containsValue(Object value);//判断是否包含某个值
V get(Object key);//获取某个键对应的值
V put(K key, V value);//添加键值对(K，V)
V remove(Object key);//移除某个键对应的键值对
void putAll(Map<? extends K, ? extends V> m);//添加另一个Map集合
void clear();//清空所有键值对
Set<K> keySet();//获取键的集合
Collection<V> values();//获取值的集合
Set<Map.Entry<K, V>> entrySet();//获取键值对实体的集合
interface Entry<K,V>//Map中的内部接口

//   HashMap<String, Student> hm = new HashMap<String, Student>();
//   hm.put("2018050401", new Student("2018050401", "张三", 18, 80.0));
//   hm.put("2018050402", new Student("2018050402", "李四", 18, 80.0));
//   hm.put("2018050403", new Student("2018050403", "李四", 18, 80.0));
//   hm.put("2018050404", new Student("2018050404", "王五", 18, 80.0));
//   hm.put("2018050404", new Student("2018050404", "王五", 18, 80.0));
//   
//   // 方式一: 通过键找值
//   Set<String> keys = hm.keySet();
//   for (String key : keys) {
//     Student s = hm.get(key);
//     System.out.println(key + "|" + s.getId() + "|" + s.getName() + "|" + s.getAge() + "|" + s.getScore());
//   }

    HashMap<Student, String> hm = new HashMap<Student, String>();
    hm.put(new Student("2018050401", "张三", 18, 80.0),"2018050401");
    hm.put(new Student("2018050402", "李四", 18, 80.0),"2018050402");
    hm.put(new Student("2018050403", "李四", 18, 80.0), "2018050403");
    hm.put(new Student("2018050404", "王五", 18, 80.0), "2018050404");
    hm.put(new Student("2018050404", "王五", 18, 80.0), "2018050404");
    
    // 方式二: 通过键值对对象找键找值
    Set<Entry<Student, String>> keyValues = hm.entrySet();
    for (Entry<Student, String> keyValue : keyValues) {
      Student s = keyValue.getKey();
      String value = keyValue.getValue();
      System.out.println(s.getId() + "|" + s.getName() + "|" + s.getAge() + "|" + s.getScore() + "=" + value);
    }

    LinkedHashMap<Integer, String> lhm = new LinkedHashMap<Integer, String>();
    lhm.put(01, "张三1");
    lhm.put(02, "张三2");
    lhm.put(03, "张三3");
    lhm.put(04, "张三4");
    lhm.put(05, "张三5");
    
    Set<Integer> keys = lhm.keySet();
    for (Integer key : keys) {
      System.out.println(key + "|" + lhm.get(key));
    }

    TreeMap<Integer, String> tm = new TreeMap<Integer, String>();
    tm.put(24, "Hello1");
    tm.put(14, "Hello2");
    tm.put(34, "Hello3");
    tm.put(124, "Hello4");
    tm.put(24, "Hello5");
    tm.put(24, "Hello6");
    tm.put(24, "Hello7");
    tm.put(244, "Hello8");
    tm.put(624, "Hello9");
    tm.put(24, "Hello10");
    Set<Integer> keys = tm.keySet();
    for (Integer key : keys) {
      String value = tm.get(key);
      System.out.println(key + "|" + value);
    }

Hashtable<String, String> hashtable = new Hashtable<String, String>();
    hashtable.put("刘备", "孙尚香");
    hashtable.put("孙策", "大乔");
    hashtable.put("周瑜", "小乔");
    hashtable.put("吕布", "貂蝉");
    System.out.println(hashtable);
    Enumeration<String> keys = hashtable.keys();
    while (keys.hasMoreElements()) {
      String key = keys.nextElement();
      String value = hashtable.get(key);
      System.out.println(key + "|" + value);
    }

    WeakHashMap<String,String> whm = new WeakHashMap<>();
    whm.put(new String("hello1"), "world1");
    whm.put(new String("hello2"), "world2");
    whm.put(new String("hello3"), "world3");
    whm.put("hello4", "world3");
    System.out.println(whm);
    System.gc();
    System.runFinalization();
    System.out.println(whm);

    EnumMap<Direction, String> em = new EnumMap<>(Direction.class);
    em.put(Direction.UP, "向上移动");
    em.put(Direction.DOWN, "向下移动");
    em.put(Direction.LEFT, "向左移动");
    em.put(Direction.RIGHT, "向右移动");
    
    Set<Direction> keys = em.keySet();
    for (Direction key : keys) {
      String value = em.get(key);
      System.out.println(key + "|" + value);
    }