HashMap取数据三种方法

 public static void main(String[] args) {
        HashMap map = new HashMap<>();
        map.put("1", "aa");
        map.put("2", "aa");
        map.put("3", "cc");
        map.put("2", "bb");

        //HashMap 取数据几种方法
        //1.取key再找。因为key是唯一，则用Set集合来存key
        Set set = map.keySet();
        Iterator it = set.iterator();
        while(it.hasNext()){
            String key = it.next();
            String value = map.get(key);
            System.out.println(key + ":" + value);
        }

        System.out.println("------");
        //2.把整个映射取出来，整个映射类型是EntrySet 即Set>，每个映射类型是Entry
        Set> entrySet = map.entrySet();
        Iterator> entryit = entrySet.iterator();
        Map.Entry entry;
        while(entryit.hasNext()){
            entry = entryit.next();
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + ":" + value);
        }

        System.out.println("------");
        //3.把值的集合取出来，因为key唯一，值不唯一，所以所有值集合是Collection
        Collection values = map.values();
        Iterator vit = values.iterator();
        while (vit.hasNext()) {
            String value = vit.next();
            System.out.println(value);
        }
    }

结果:

1:aa
2:bb
3:cc
------
1:aa
2:bb
3:cc
------
aa
bb
cc