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Java List对象集合按对象属性分组、分组汇总、过滤等操作示例

Go_Viola 2022-02-13 阅读 135


import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Test {
public static void main(String[] args){
List<PersonData> list = new ArrayList<PersonData>();
PersonData p1 = new PersonData();
p1.setId("1");
p1.setName("张三");
p1.setType("管理员");
p1.setAge(20);
list.add(p1);

PersonData p2 = new PersonData();
p2.setId("2");
p2.setName("李四");
p2.setType("管理员");
p2.setAge(30);
list.add(p2);

PersonData p3 = new PersonData();
p3.setId("3");
p3.setName("王五");
p3.setType("用户");
p3.setAge(40);
list.add(p3);

PersonData p4 = new PersonData();
p4.setId("4");
p4.setName("马六");
p4.setType("访客");
p4.setAge(50);
list.add(p4);

//跟据某个属性分组
Map<String, List<PersonData>> collect = list.stream().collect(Collectors.groupingBy(PersonData::getType));
System.out.println(collect);

//根据某个属性分组,汇总某个属性
Map<String, Integer> collect2 = list.stream().collect(Collectors.groupingBy(PersonData::getType,Collectors.summingInt(PersonData::getAge)));
System.out.println(collect2);

//根据某个属性添加条件过滤数据,
list = list.stream().filter(u -> !u.getType().equals("访客")).collect(Collectors.toList());
System.out.println(list);

//判断一组对象里面有没有属性值是某个值
boolean add = list.stream().anyMatch(m -> "王五".equals(m.getName()));
System.out.println(add);

//取出一组对象的某个属性组成一个新集合
List<String> names=list.stream().map(PersonData::getName).collect(Collectors.toList());
System.out.println(names);
}
}

结果输出:


{用户=[com.test4.PersonData@19a45b3], 访客=[com.test4.PersonData@99a589], 管理员=[com.test4.PersonData@372a00, com.test4.PersonData@dd8dc3]}
{用户=40, 访客=50, 管理员=50}
[com.test4.PersonData@372a00, com.test4.PersonData@dd8dc3, com.test4.PersonData@19a45b3]
true
[张三, 李四, 王五]


public class PersonData {
private String id;
private String type;
private String name;
private int age;

public String getId() {
return id;
}

public void setId(String id) {
this.id = id;
}

public String getType() {
return type;
}

public void setType(String type) {
this.type = type;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public PersonData(String id, String type, String name, int age) {
super();
this.id = id;
this.type = type;
this.name = name;
this.age = age;
}

public PersonData() {

}
}



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