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。

来源：博客园

作者：zhjh256

链接：https://www.cnblogs.com/zhjh256/p/11626524.html