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HashMap的四种访问方式
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第一種：通過Map.entrySet使用iterator遍歷key和value
?
1 public void visit_1(HashMap<String,Integer>
hm){
2 Iterator<Map.Entry<String,Integer>> it =
hm.entrySet().iterator();
3 while(it.hasNext()){
4 Map.Entry<String ,Integer> entry =
it.next();
5 String key =
entry.getKey();
6 Integer value =
entry.getValue();
7 }
8 }
?
第二種：通過Key來遍歷value
1 public void visit_2(HashMap<String,Integer>
hm){
2 for (String key:hm.keySet()){
3 Integer value =
hm.get(key);
4 }
5 }
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第三種：通過Map.Entry遍歷key和value
1 public void visit_3(HashMap<String,Integer>
hm){
2 for(Map.Entry<String,Integer>
entry:hm.entrySet()){
3 String key =
entry.getKey();
4 Integer value =
entry.getValue();
5 }
6 }
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第四種：通過Map.keySet使用iterator遍歷key和value
1 public void visit_4(HashMap<Integer,String>
hm){
2 long startTime =
System.currentTimeMillis();
3 Iterator<Integer> it =
hm.keySet().iterator();
4 while(it.hasNext()){
5 Integer key =
it.next();
6 String value =
hm.get(key);
7 }
8 System.out.println("visit_4 10000000 entry:"
9 + (System.currentTimeMillis()-startTime) + " milli seconds"
);
10 }
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四種方法比較：
1 package chapter08.c86.c862;
2
3 import java.util.HashMap;
4 import java.util.Iterator;
5 import java.util.Map;
6
7 /**
8 * Created by ceoicac on 2017/8/12 10:22.
9 */
10 public class HashMapVisitTest {
11 public void visit_1(HashMap<Integer,String>
hm){
12 long startTime =
System.currentTimeMillis();
13 Iterator<Map.Entry<Integer,String>> it =
hm.entrySet().iterator();
14 while(it.hasNext()){
15 Map.Entry<Integer,String> entry =
it.next();
16 Integer key =
entry.getKey();
17 String value =
entry.getValue();
18 }
19 System.out.println("visit_1 10000000 entry:"
20 + (System.currentTimeMillis()-startTime) + " milli seconds"
);
21 }
22 public void visit_2(HashMap<Integer,String>
hm){
23 long startTime =
System.currentTimeMillis();
24 for (Integer key:hm.keySet()){
25 String value =
hm.get(key);
26 }
27 System.out.println("visit_1 10000000 entry:"
28 + (System.currentTimeMillis()-startTime) + " milli seconds"
);
29 }
30 public void visit_3(HashMap<Integer,String>
hm){
31 long startTime =
System.currentTimeMillis();
32 for(Map.Entry<Integer,String>
entry : hm.entrySet()){
33 Integer key =
entry.getKey();
34 String value =
entry.getValue();
35 }
36 System.out.println("visit_1 10000000 entry:"
37 + (System.currentTimeMillis()-startTime) + " milli seconds"
);
38 }
39 public void visit_4(HashMap<Integer,String>
hm){
40 long startTime =
System.currentTimeMillis();
41 Iterator<Integer> it =
hm.keySet().iterator();
42 while(it.hasNext()){
43 Integer key =
it.next();
44 String value =
hm.get(key);
45 }
46 System.out.println("visit_1 10000000 entry:"
47 + (System.currentTimeMillis()-startTime) + " milli seconds"
);
48 }
49 public static void main(String [] args){
50 HashMap<Integer,String> hm =
new HashMap<>
();
51 for(
int i = 1;i <= 10000000;++
i){
52 hm.put(i,"num: " +
i);
53 }
54 new HashMapVisitTest().visit_1(hm);
55 new HashMapVisitTest().visit_2(hm);
56 new HashMapVisitTest().visit_3(hm);
57 new HashMapVisitTest().visit_4(hm);
58
59 }
60 }
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結(jié)果：
作者：ceoicac
來源：CSDN
原文：https://blog.csdn.net/ceoicac/article/details/77113068
版權(quán)聲明：本文為博主原創(chuàng)文章，轉(zhuǎn)載請附上博文鏈接！
轉(zhuǎn)載于:https://www.cnblogs.com/KeepDoingSomething/p/9904140.html
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