HashMap的四种循环遍历方式

public static void main(String[] args){
        HashMap hashMap = new HashMap();
        hashMap.put(1, 1);
        hashMap.put(2, 2);
        //* 4种hashMap循环方式
        // for each map.entrySet()
        for(Entry entry : hashMap.entrySet()){
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }
        //for each map.entrySet()，用临时变量保存map.entrySet()
        Set> maps = hashMap.entrySet();
        for(Entry entry : maps){
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }
        //显示调用map.entrySet()的集合迭代器
        Iterator> iterator2 = hashMap.entrySet().iterator();
        while(iterator2.hasNext()){
            Entry entry = iterator2.next();
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }
        // for each map.keySet()，再调用get获取
        for(Integer key : hashMap.keySet()){
            System.out.println(key);
            System.out.println(hashMap.get(key));
        }
    }