阿里巴巴建议这样遍历Map,今天就用几种方式做个比较一下看那种最好用

// Map初始化 private static Map<String,Integer> initMap(int count{ AlternativeJdkIdGenerator alternativeJdkIdGenerator = new AlternativeJdkIdGenerator(; Map<String,Integer> map = new HashMap<>(; for (int i = 0; i < count; i++ { map.put(alternativeJdkIdGenerator.generateId(.toString(,i ; } return map ; }

int count = 1000000;
        Map<String,Integer> map =initMap(count ;
        // 为了计算平均值，分别循环三次进行遍历
        for (int i = 0; i < 3; i++ {
            Instant start;
            Instant end;
            start = Instant.now(;
            for (Map.Entry<String, Integer> entry : map.entrySet( {
                // 一般遍历map就是获取key和value
                String  result="key为："+entry.getKey(+"，value为："+entry.getValue(;
            }
            end = Instant.now(;
            System.out.println("遍历循环" + count + "次耗时：" + Duration.between(start, end.toMillis( + "ms";
        }

int count = 1000000; Map<String,Integer> map =initMap(count ; for (int i = 0; i < 3; i++ { Instant start; Instant end; start = Instant.now(; for (Iterator<Map.Entry<String,Integer>> entries = map.entrySet(.iterator(; entries.hasNext(; { Map.Entry<String,Integer> entry = entries.next(; String result ="key为："+entry.getKey(+"，value为："+entry.getValue(; } end = Instant.now(; System.out.println("遍历循环" + count + "次耗时：" + Duration.between(start, end.toMillis( + "ms"; }

 int count = 1000000;
        Map<String,Integer> map =initMap(count ;
        for (int i = 0; i < 3; i++ {
            Instant start;
            Instant end;
            start = Instant.now(;
            for (String key : map.keySet( {
                String result ="key为："+key+"，value为："+map.get(key;
            }
            end = Instant.now(;
            System.out.println("遍历循环" + count + "次耗时：" + Duration.between(start, end.toMillis( + "ms";
        }

  int count = 1000000;
        Map<String,Integer> map =initMap(count ;
        for (int i = 0; i < 3; i++ {
            Instant start;
            Instant end;
            start = Instant.now(;
            for (Iterator<String> key = map.keySet(.iterator(; key.hasNext(;  {
                String k = key.next(;
                String result ="key为："+k+"，value为："+map.get(k;
            }
            end = Instant.now(;
            System.out.println("遍历循环" + count + "次耗时：" + Duration.between(start, end.toMillis( + "ms";
        }

int count = 1000000; Map<String,Integer> map =initMap(count ; for (int i = 0; i < 3; i++ { Instant start; Instant end; start = Instant.now(; map.forEach((key, value -> { String result ="key为："+key+"，value为："+map.get(value; }; end = Instant.now(; System.out.println("遍历循环" + count + "次耗时：" + Duration.between(start, end.toMillis( + "ms"; }