【Java基础】HashMap的四种遍历以及耗时对比

HashMap的四种遍历以及耗时对比

1.method1

public static void method1(Map<String, Object> map) {
getTime();
Set<String> keySet = map.keySet();//键集合
Iterator<String> it = keySet.iterator();//迭代器
while(it.hasNext()) {
String key = it.next();
Object value = map.get(key);
//			System.out.println(key+"_"+value);
}
getTime();
}

2.method2

public static void method2(Map<String,Object> map) {
getTime();
for(String key : map.keySet()) {
Object value = map.get(key);
//			System.out.println(key+"_"+value);
}
getTime();
}

3.method3

public static void method3(Map<String,Object> map) {
getTime();
Set<Entry<String, Object>> entrySet = map.entrySet();
Iterator<Entry<String, Object>> it = entrySet.iterator();
while(it.hasNext()) {
Entry<String, Object> next = it.next();
String key = next.getKey();
Object value = next.getValue();
//			System.out.println(key+"_"+value);
}
getTime();
}

4.method4

public static void method4(Map<String,Object> map) {
getTime();
for(Map.Entry<String, Object> entry : map.entrySet()) {
String key = entry.getKey();
Object value = entry.getValue();
//			System.out.println(key+"_"+value);
}
getTime();
}

5.耗时对比

6.整体代码

package hashMap;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
/**
*
* @author wsz
* @date 2017年12月12日
耗时单位ms
----------------------------------
数据量     5W      50W     500W
----------------------------------
method1   8       25   203-180-178
----------------------------------
method2   11      24   201-198-187
----------------------------------
method3   10      21   145-137-136
----------------------------------
method4   9       21   151-135-136
----------------------------------

*/
public class Demo1 {

public static void main(String[] args) {
Map<String,Object> map = new HashMap<String, Object>();
long size = 10000000L;
for(int i = 0; i < size ;i++) {
map.put(String.valueOf(i), i);
}

method1(map);
method2(map);
method3(map);
method4(map);
}

public static void method1(Map<String, Object> map) {
getTime();
Set<String> keySet = map.keySet();//键集合
Iterator<String> it = keySet.iterator();//迭代器
while(it.hasNext()) {
String key = it.next();
Object value = map.get(key);
//			System.out.println(key+"_"+value);
}
getTime();
}

public static void method2(Map<String,Object> map) {
getTime();
for(String key : map.keySet()) {
Object value = map.get(key);
//			System.out.println(key+"_"+value);
}
getTime();
}

public static void method3(Map<String,Object> map) {
getTime();
Set<Entry<String, Object>> entrySet = map.entrySet();
Iterator<Entry<String, Object>> it = entrySet.iterator();
while(it.hasNext()) {
Entry<String, Object> next = it.next();
String key = next.getKey();
Object value = next.getValue();
//			System.out.println(key+"_"+value);
}
getTime();
}

public static void method4(Map<String,Object> map) {
getTime();
for(Map.Entry<String, Object> entry : map.entrySet()) {
String key = entry.getKey()
986e
;
Object value = entry.getValue();
//			System.out.println(key+"_"+value);
}
getTime();
}

public static void getTime() {
System.out.println(System.currentTimeMillis());
}
}