HashMap遍历

HashMap的遍历总共可以分为以下四类

• Iterator遍历
• For Each遍历
• Lambda表达式遍历
• Stream API遍历

Iterator迭代器遍历

Iterator结合entrySet遍历

// Iterator 结合entry遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        Iterator<Map.Entry<Integer, String>> iterator = hashMap.entrySet().iterator();
       while (iterator.hasNext()) {
           Map.Entry<Integer, String> entry = iterator.next();
           System.out.println(entry.getKey());
           System.out.println(entry.getValue());
       }

Iterator结合keySet遍历

// Iterator 结合keyset遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        Iterator<Integer> iterator = hashMap.keySet().iterator();
        while (iterator.hasNext()) {
            int key = iterator.next();
            System.out.println(hashMap.get(key));
        }

For Each遍历

For Each结合entrySet遍历

 // for 结合entrySet遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        for (Map.Entry<Integer, String> entry : hashMap.entrySet()) {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());

        }

For Each结合keySet遍历

// for 结合keySet遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        for (Integer key : hashMap.keySet()) {
            System.out.println(key);
            System.out.println(hashMap.get(key));

        }

Lambda表达式遍历

// Lambda表达式遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        hashMap.forEach((key, value) -> {
            System.out.println(key);
            System.out.println(value);
        });

Stream API遍历

Stream API单线程遍历

// Streanms API单线程遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        hashMap.entrySet().stream().forEach((entry) -> {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        });

Stream API多线程遍历

// Streanms API多线程遍历HashMap
        Map<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "a");
        hashMap.put(2, "b");
        hashMap.put(3, "c");
        System.out.println(hashMap);
        hashMap.entrySet().parallelStream().forEach((entry) -> {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        });

参考：

• HashMap 的 7 种遍历方式与性能分析！「修正篇」