标签：性能优化 out temp 比较 public edm ++ oid count
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。
java性能优化之HashMap，LinkedHashMap，TreeMap读取大量数据效率的比较
标签：性能优化 out temp 比较 public edm ++ oid count
原文地址：https://www.cnblogs.com/zhjh256/p/11626524.html
