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  • java性能优化之HashMap,LinkedHashMap,TreeMap读取大量数据效率的比较

    很多时候,我们用jdbctemplate或mybatis的时候,为了查询通用,会选择使用map数据结构,因为hashmap本身无序,所以为了保证key的有序性,会采用linkedhashmap。所以我们要看一下Linkedhashmap的性能影响多大。如下:

        @Test
        public void test() {
            Integer count =1000000;
            Random random =new Random();
            Map<String, String> map = new HashMap<String, String>();
            for (int i = 0; i < count; i++) {
                map.put(i+"", i+"");
            }
            long time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                map.get((random.nextInt(count)+1)+"");
            }
            long time2 = System.currentTimeMillis();
            System.out.println("HashMap time:" + (time2 - time1));
            ////////////////////////////////////////////////////////////////////////
            Map<String, String> linkedMap = new LinkedHashMap<String, String>();
            for (int i = 0; i < count; i++) {
                linkedMap.put(i+"", i+"");
            }
     
            time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                 linkedMap.get((random.nextInt(count)+1)+"");
            }
            time2 = System.currentTimeMillis();
            System.out.println("LinkedHashMap time:" + (time2 - time1));
                    ////////////////////////////////////////////////////////////////////////
            Map<String, String> treeMap = new TreeMap<String, String>();
            for (int i = 0; i < count; i++) {
                treeMap.put(i+"", i+"");
            }
     
            time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                treeMap.get((random.nextInt(count)+1)+"");
            }
            time2 = System.currentTimeMillis();
            System.out.println("TreeMap time:" +  (time2 - time1));
        }

    执行结果:

    HashMap time:641
    LinkedHashMap time:703
    TreeMap time:4040

    读取数据是有序,则如下:

        @Test
        public void test2() {
            Integer count =1000000;
            Random random =new Random();
            Map<String, String> map = new HashMap<String, String>();
            for (int i = 0; i < count; i++) {
                map.put(i+"", i+"");
            }
            long time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                map.get(i+"");
            }
            long time2 = System.currentTimeMillis();
            System.out.println("HashMap time:" + (time2 - time1));
            ////////////////////////////////////////////////////////////////////////
            Map<String, String> linkedMap = new LinkedHashMap<String, String>();
            for (int i = 0; i < count; i++) {
                linkedMap.put(i+"", i+"");
            }
     
            time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                 linkedMap.get(i+"");
            }
            time2 = System.currentTimeMillis();
            System.out.println("LinkedHashMap time:" + (time2 - time1));
            ////////////////////////////////////////////////////////////////////////
            Map<String, String> treeMap = new TreeMap<String, String>();
            for (int i = 0; i < count; i++) {
                treeMap.put(i+"", i+"");
            }
     
            time1 = System.currentTimeMillis();
            for (int i = 0; i < count; i++) {
                treeMap.get(i+"");
            }
            time2 = System.currentTimeMillis();
            System.out.println("TreeMap time:" +  (time2 - time1));
        }

    HashMap time:297
    LinkedHashMap time:203
    TreeMap time:438

    从上可知,LinkedHashMap是可以完全代替HashMap的,不用担心性能问题。

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  • 原文地址:https://www.cnblogs.com/zhjh256/p/11626524.html
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