map遍历

Posted 2021-11-30 renjianjun

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向map中添加数据 150万
        Map<String,String> m = new HashMap<>();
        for (int i = 0; i < 1500000; i++) {
            m.put("a" + i,"1");
        }


        long start2 = System.currentTimeMillis();
        Set<Map.Entry<String, String>> entries1 = m.entrySet();
        Iterator<Map.Entry<String, String>> iterator = entries1.iterator();
        while (iterator.hasNext()){
            Map.Entry<String, String> next = iterator.next();
            System.out.println(next.getKey() + next.getValue());
        }
        long iteratorTime = System.currentTimeMillis() - start2;


        long start = System.currentTimeMillis();for (Map.Entry<String, String> entry : m.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
        long entrySetTime = System.currentTimeMillis() - start;



        long start1 = System.currentTimeMillis();
        for (String s : m.keySet()) {
            System.out.println(s + " " + m.get(s));
        }
        long keySetTime = System.currentTimeMillis() - start1;



        System.out.println("iteratorTime" + iteratorTime);
        System.out.println("entrySetTime" + entrySetTime);
        System.out.println("keySetTime" + keySetTime);


第一次运行的结果：