【Java基础】Map的三种遍历方式

方式一：使用entrySet实现Map的遍历

        Map<String,String> map=new HashMap<String,String>();
        map.put("周","杰伦");
        map.put("方","文山");

        for (Map.Entry<String,String> entry:map.entrySet()){
            String mapkey=entry.getKey();
            String mapValue=entry.getValue();
            System.out.println(mapkey+":"+mapValue);
            }

方式二：在for循环中遍历key或者values，一般只适用于只需要map中的key或者value时使用，在性能上比使用entrySet较好

        Map<String,String> map=new HashMap<String,String>();
        map.put("周","杰伦");
        map.put("方","文山");

        //key
        for (String key:map.keySet()){
            String value=map.get(key);
            System.out.println(key+":"+value);
        }

        System.out.println("-----------------");
        
        //value
        for (String value:map.values()){
            System.out.println(value);
        }

方式三：通过Iterator遍历

        Map<String,String> map=new HashMap<String,String>();
        map.put("周","杰伦");
        map.put("方","文山");

        Iterator<Map.Entry<String,String>> entryIterator=map.entrySet().iterator();
        while(entryIterator.hasNext()){
            Map.Entry<String,String> entry=entryIterator.next();
            String key=entry.getKey();
            String value=entry.getValue();
            System.out.println(key+":"+value);
        }