java双重for循环 效率_java8的新特性之List集合双层for循环效率优化
首先先来一个案例简单模拟一下：
Listwifes = new ArrayList();
Listhusbands= new ArrayList();
for(int i=0;i<8000;i++){
wifes.add(new Wife(i, i+"的妻子", "000"+i));
}
for(int i=0;i<8000;i++){
husbands.add(new Husband(i, "我是"+i, "000"+i));
}
//现在需要让妻子和丈夫进行配对组成一个家庭，按照familyId进行配对
在1.8之前你会这么写：
for(int i=0;i
如果按照jdk1.8的lamada表达式进行匹配的话。这个测试结果是ms级别的
// 将list转为Map,这里key一定要为唯一值，map(familyId,wife对象)
MapwifeMap = wife.stream().collect(
Collectors.toMap(w -> w.getFamilyId(),
w -> w));
// 匹配家庭
families = husband.stream().map(h -> {
//从wifeMap里面根据husband的familyId去匹配。匹配上后组装成家庭对象然后放入集合。最后生成新的家庭集合
return toFamily(wifeMap.get(h.getFamilyId()), h);
}).collect(Collectors.toList());
这是个测试案例：亲测如下:
package com.nuanshui.frms.report.manage;
import com.google.common.collect.Lists;
import org.junit.Test;
import java.math.BigDecimal;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/**
* Author:
* Date: 2016/11/23.
* Time: 18:17
*/
public class TestFamily {
@Test
public void familyTest() {
Listwife = Lists.newArrayList();
Listhusband = Lists.newArrayList();
for(int i=0;i<8000;i++){
wife.add(new Wife(i, i+"的妻子", "000"+i));
}
for(int i=0;i<8000;i++){
husband.add(new Husband(i, "我是"+i, "000"+i));
}
Long startTime =System.currentTimeMillis();
System.out.println("当前时间:"+startTime);
Listfamilies = Lists.newArrayList();
// 将list转为Map,这里key一定要为唯一值
MapwifeMap = wife.stream().collect(
Collectors.toMap(w -> w.getFamilyId(),
w -> w));
// 匹配家庭
families = husband.stream().map(h -> {
return toFamily(wifeMap.get(h.getFamilyId()), h);
}).collect(Collectors.toList());
/*for(int i=0;i{
System.out.println("家庭ID：" + family.getFamilyId() + ",丈夫：" + family.getHusbandName() + ",妻子：" + family.getWifeName());
});
Long endTime =System.currentTimeMillis();
System.out.println("结束时间:"+endTime);
System.out.println("------------耗时:---------"+(endTime-startTime)+"ms");
}
private Family toFamily(Wife wife, Husband husband) {
Family family = new Family();
family.setFamilyId(wife.getFamilyId());
family.setHusbandName(husband.getHusbandName());
family.setWifeName(wife.getWifeName());
return family;
}
@Test
public void test1(){
//String.valueOf()
BigDecimal c = new BigDecimal(651000);
BigDecimal d = new BigDecimal(312);
BigDecimal num3 = c.divide(d,10,BigDecimal.ROUND_HALF_DOWN);
System.out.println(num3);
BigDecimal b = (new BigDecimal(651000).divide(new BigDecimal(312)).setScale(1, BigDecimal.ROUND_HALF_UP));
System.out.println(b);
}
}
结果只要252ms；
这种效率天差地别。