Java中Map遍历的九种方式汇总

public static void testMap1(Map<Integer, Integer> map) {
    long sum = 0;
    for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
      sum += entry.getKey() + entry.getValue();
    }
    System.out.println(sum);
  }

public static void testMap2(Map<Integer, Integer> map) {
    long sum = 0;
    for (Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator(); entries.hasNext(); ) {
      Map.Entry<Integer, Integer> entry = entries.next();
      sum += entry.getKey() + entry.getValue();
    }
    System.out.println(sum);
  }

 public static void testMap3(Map<Integer, Integer> map) {
    Iterator<Map.Entry<Integer, Integer>> it = map.entrySet().iterator();
    long sum = 0;
    while (it.hasNext()) {
      Map.Entry<Integer, Integer> entry = it.next();
      sum += entry.getKey() + entry.getValue();
    }
    System.out.println(sum);
  }

public static void testMap4(Map<Integer, Integer> map) {
    long sum = 0;
    for (Integer key : map.keySet()) {
      sum += key + map.get(key);
    }
    System.out.println(sum);
  }

public static void testMap5(Map<Integer, Integer> map) {
    long sum = 0;
    for (Iterator<Integer> key = map.keySet().iterator(); key.hasNext(); ) {
      Integer k = key.next();
      sum += k + map.get(k);
    }
    System.out.println(sum);
  }

public static void testMap6(Map<Integer, Integer> map) {
    Iterator<Integer> it = map.keySet().iterator();
    long sum = 0;
    while (it.hasNext()) {
      Integer key = it.next();
      sum += key + map.get(key);
    }
    System.out.println(sum);
  }

public static void testMap7(Map<Integer, Integer> map) {
    final long[] sum = {0};
    map.forEach((key, value) -> {
      sum[0] += key + value;
    });
    System.out.println(sum[0]);
  }

public static void testMap8(Map<Integer, Integer> map) {
    long sum = map.entrySet().stream().mapToLong(e -> e.getKey() + e.getValue()).sum();
    System.out.println(sum);
  }

 public static void testMap9(Map<Integer, Integer> map) {
    long sum = map.entrySet().parallelStream().mapToLong(e -> e.getKey() + e.getValue()).sum();
    System.out.println(sum);
  }

public static void main(String[] args) {
   int outSize = 1;
    int mapSize = 200;
    Map<Integer, Integer> map = new HashMap<>(mapSize);
    for (int i = 0; i < mapSize; i++) {
      map.put(i, i);
    }
    System.out.println("---------------start------------------");
    long totalTime = 0;
    for (int size = outSize; size > 0; size--) {
      long startTime = System.currentTimeMillis();
      testMap1(map);
      totalTime += System.currentTimeMillis() - startTime;
    }
    System.out.println("testMap1 avg time is :" + (totalTime / outSize));
		// 省略其他方法，代码跟上面一致
}