Map和EntrySet、keySet的迭代效率

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虚拟机环境：

操作系统：win7

平台：eclipse 3.7

实验目的：对比Map和EntrySet、keySet的迭代效率，从而对比得出map效率较高的迭代方式。

实现方式：通过迭代相同的map，分别记录迭代的开始和结束时间，对比两种迭代的总耗时，得出结论。

实验结果： 10000次测试中keySet用时2999次大于entry用时

10000次测试中entry用时2323次大于keySet用时

10000次测试中用时相等4678次

实验结果：entrySet 迭代效率更高

实验代码：

public class Apple {private String name;private String id;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getId() {return id;}public void setId(String id) {this.id = id;}}

public class Test {public static void main(String[] args) {Map<String, Apple> map = new HashMap<String, Apple>();Random random = new Random();int resultBig = 0;int resultEqul = 0;int total = 10000; for (int round = 0; round < total; round++) {int rand = random.nextInt(90000);for (int i = 0; i < rand; i++) {map.put("data" + i, new Apple());}long sumTime1 = 0;// keySet方法用时long sumTime2 = 0;// entry方法用时long startTime1 = 0;// keySet方法开始时间long startTime2 = 0;// entry方法开始时间Iterator<String> keys = map.keySet().iterator();startTime1 = System.currentTimeMillis();while (keys.hasNext()) {String key = (String) keys.next();Apple val = map.get(key);// System.out.println(key + " : " + val);}sumTime1 = System.currentTimeMillis() - startTime1;System.out.println("keySet: " + sumTime1);Iterator<Entry<String, Apple>> iter = map.entrySet().iterator();startTime2 = System.currentTimeMillis();while (iter.hasNext()) {Entry<String, Apple> entry = iter.next();String a = entry.getKey();Apple b = entry.getValue();// System.out.println(a + " : " + b);}sumTime2 = System.currentTimeMillis() - startTime2;System.out.println("entry: " + sumTime2);System.out.println("----------------"+ "map数据量： " + rand + "------------------------");if(sumTime1 > sumTime2){resultBig++;}else if(sumTime1 == sumTime2){resultEqul++;}}System.out.println(total + "次测试中" + "keySet用时" + resultBig + "次大于entry用时");System.out.println(total + "次测试中" + "entry用时" + (total-resultBig-resultEqul) + "次大于keySet用时");System.out.println(total + "次测试中" + "用时相等" + resultEqul + "次");}}

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