Java 7 和 Java 8 对 list 的双层循环处理
作者:互联网
一、准备
Java 处理 List 的双层循环,一般都是当两个 List 某个值满足某条件时候,进行相应的处理。需求:两个 List 对象当 id 相同的时候就组建成美好的家庭,Husband 对象与 Wife 对象组建成 Family 对象。
Husband 对象如下:
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ApiModel(value = "丈夫")
public class Husband {
@ApiModelProperty(value = "家庭ID")
private int familyId;
@ApiModelProperty(value = "丈夫名称")
private String husbandName;
@ApiModelProperty(value = "妻子名称")
private String wifeName;
}
Wife 对象如下:
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ApiModel(value = "妻子")
public class Wife {
@ApiModelProperty(value = "家庭ID")
private int familyId;
@ApiModelProperty(value = "丈夫名称")
private String husbandName;
@ApiModelProperty(value = "妻子名称")
private String wifeName;
}
Family 对象如下:
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ApiModel(value = "家庭")
public class Family {
@ApiModelProperty(value = "家庭ID")
private int familyId;
@ApiModelProperty(value = "丈夫名称")
private String husbandName;
@ApiModelProperty(value = "妻子名称")
private String wifeName;
}
二、对比
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class FamilyDemo {
public static void main(String[] args) {
List<Wife> wives = new ArrayList<>();
List<Husband> husbands = new ArrayList<>();
for (int i = 0; i < 10000; i++) {
wives.add(new Wife(i, i + "的妻子", "000" + i));
}
for (int i = 0; i < 10000; i++) {
husbands.add(new Husband(i, "我是" + i, "000" + i));
}
FamilyDemo familyDemo = new FamilyDemo();
familyDemo.testJava7(wives, husbands);
familyDemo.testJava8(wives, husbands);
}
public void testJava7(List<Wife> wives, List<Husband> husbands) {
List<Family> families = new ArrayList<>();
for (int i = 0; i < wives.size(); i++) {
Wife wife = wives.get(i);
for (int j = 0; j < husbands.size(); j++) {
Husband husband = husbands.get(j);
if (wife.getFamilyId() == husband.getFamilyId()) {
Family family = new Family();
family.setFamilyId(husband.getFamilyId());
family.setHusbandName(husband.getHusbandName());
family.setWifeName(husband.getWifeName());
families.add(family);
}
}
}
System.out.println("Java7结合家庭数量:" + families.size());
System.out.println(families);
}
public void testJava8(List<Wife> wives, List<Husband> husbands) {
List<Family> families = new ArrayList<>();
//将list转为Map,这里key必须是唯一的,即familyId
Map<Integer, Wife> wifeMap = wives.stream().collect(Collectors.toMap(w -> w.getFamilyId(), w -> w));
families = husbands.stream().map(h -> {
Family family = new Family();
Wife wife = wifeMap.get(h.getFamilyId());
family.setFamilyId(wife.getFamilyId());
family.setHusbandName(wife.getHusbandName());
family.setWifeName(wife.getWifeName());
return family;
}).collect(Collectors.toList());
System.out.println("Java8完美结合家庭数量:" + families.size());
families.stream().forEach(family -> {
System.out.println("家庭ID:" + family.getFamilyId());
});
}
}
对比下来,stream 效率明显提升了很多,尤其数据量大的时候效率提升得越高。
标签:Java,family,List,list,value,ApiModelProperty,import,lombok,双层 来源: https://blog.csdn.net/ChineseSoftware/article/details/123073107