/*
    添加、刪除、修改操作：
    Object put(Object key,Object value): 將指定key-value添加到(或修改)當(dāng)前map對象中
    void putAll(Map m):將m中的所有key-value對存放到當(dāng)前map中
    Object remove(Object key):移除指定key的key-value對，并返回value
    void clear():清空當(dāng)前map中的所有數(shù)據(jù)
     */
    public void test1(){
        HashMap map = new HashMap();
        //添加
        map.put("AA",123);
        map.put(45,123);
        map.put("BB",56);
        //修改
        map.put("AA",87);
        System.out.println(map);//{AA=87, BB=56, 45=123}
        HashMap map1 = new HashMap();
        map.put("CC",123);
        map.put("DD",123);
        map.putAll(map1);
        System.out.println(map);//{AA=87, BB=56, CC=123, DD=123, 45=123}
        //remove(Object key)
        Object value = map.remove("CC");
        System.out.println(value);//123
        System.out.println(map);//{AA=87, BB=56, DD=123, 45=123}
        //clear()
        map.clear();//與map = null操作不同；map對象還在，只是里面的數(shù)據(jù)沒了
        System.out.println(map.size());//0
        System.out.println(map);//{}
    }

 /*
    元素查詢的操作：
    Object get(Object key):獲取指定key對應(yīng)的value
    boolean containsKey(Object key):是否包含指定的value
    int size():返回map中key-value對的個數(shù)
    boolean isEmpty():判斷當(dāng)前map是否為空
    boolean equals(Object obj):判斷當(dāng)前map和參數(shù)對象obj是否相等
     */
    public void test2(){
        HashMap map = new HashMap();
        map.put("AA",123);
        map.put(45,123);
        map.put("BB",56);
        //Object get(Object key)
        System.out.println(map.get(45));//123
        //containsKey(Object key)
        boolean isExit = map.containsKey("BB");
        System.out.println(isExit);//true
        isExit = map.containsValue(123);
        System.out.println(isExit);//true
        map.clear();
        System.out.println(map.isEmpty());//true
    }

/*
    元視圖操作的方法：
    Set keySet():返回所有key構(gòu)成的Set集合
    Collection values(): 返回所有value構(gòu)成的Collection集合
    Set entrySet():返回所有key-value對構(gòu)成的Set集合
     */
    public void test3(){
        HashMap map = new HashMap();
        map.put("AA",123);
        map.put(45,123);
        map.put("BB",56);
        //遍歷所有的key集：keySet()
        Set set = map.keySet();
        Iterator iterator = set.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next());//AA BB 45
        }
        System.out.println();
        //遍歷所有的value集：value()
        Collection values = map.values();
        for(Object obj : values){
            System.out.println(obj);// 123 56 123
        }
        System.out.println();
        //遍歷所有的key-value
        //方式一：entrySet()
        Set entrySet = map.entrySet();
        Iterator iterator1 = entrySet.iterator();
        while(iterator1.hasNext()){
            Object obj = iterator1.next();
            //entrySet集合中的元素都是entry
            Map.Entry entry = (Map.Entry)obj;
            System.out.println(entry.getKey() + "---->" + entry.getValue());
            //AA---->123
            //BB---->56
            //45---->123
        }
        System.out.println();
        //方式二：
        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);
            //AA======123
            //BB======56
            //45======123
        }
    }

源碼中：
      static class Entry<K,V> extends HashMap.Node<K,V>{
          Entry<K,V> before,after;//能夠記錄添加的元素的先后順序
          Entry(int hash, K key, V value,Node<K,V> next){
          super(hash, key, value, next);
          }
      }

 //向TreeMap中添加key-value,要求key必須是有同一個類創(chuàng)建的對象
    //因為要按照key進(jìn)行排序：自然排序、定制排序
    @Test
    public void test1() {
        TreeMap map = new TreeMap();
        User u1 = new User("Tom", 23);
        User u2 = new User("Jerry", 32);
        User u3 = new User("Jack", 20);
        User u4 = new User("Rose", 18);
        map.put(u1, 98);
        map.put(u2, 89);
        map.put(u3, 76);
        map.put(u4, 100);
        Set entrySet = map.entrySet();
        Iterator iterator1 = entrySet.iterator();
        while (iterator1.hasNext()) {
            Object obj = iterator1.next();
            //entrySet集合中的元素都是entry
            Map.Entry entry = (Map.Entry) obj;
            System.out.println(entry.getKey() + "---->" + entry.getValue());
            //User{name='Jack', age=20}---->76
            //User{name='Jerry', age=32}---->89
            //User{name='Rose', age=18}---->100
            //User{name='Tom', age=23}---->98
        }
    }

public void test1(){
        ArrayList list = new ArrayList();
        list.add(123);
        list.add(43);
        list.add(765);
        list.add(765);
        list.add(765);
        list.add(-97);
        list.add(0);
        System.out.println(list);
//        Collections.reverse(list);
//        Collections.shuffle(list);
//        Collections.swap(list,1,2);
        int frequency = Collections.frequency(list, 765);
        System.out.println(list);
        System.out.println(frequency);
        /*
        Collections類中提供了多個synchronizedXxx()方法，該方法可使將指定集合包裝成線程同步的集合，從而可以解決多線程
        并發(fā)訪問集合時的線程安全問題
         */
        List list1 = Collections.synchronizedList(list);
    }

public void test2(){
        List list = new ArrayList();
        list.add(123);
        list.add(43);
        list.add(765);
        list.add(-97);
        list.add(0);
        //報異常:IndexOutOfBoundsException
//        List dest = new ArrayList();
//        Collections.copy(dest,list);
        //正確的：
        List  dest = Arrays.asList(new Object[list.size()]);
        System.out.println(dest.size());
        Collections.copy(dest,list);//5
        System.out.println(dest);//[123, 43, 765, -97, 0]
    }