List中对象属性去重的方法

摘抄大佬：List根据对象属性去重

 一、去除List中重复的String

 使用set集合 

List stringList = Arrays.asList("1", "2","3","1","1","1","1");
        
Set set = new LinkedHashSet<>();
set.addAll(stringList);

stringList.clear();
stringList.addAll(set);
System.out.println(stringList);

 报错异常：解惑答疑

        List stringList = Arrays.asList("1", "2","3","1","1","1","1");
        Set set = new LinkedHashSet<>();
        set.addAll(stringList);

//       stringList.clear();
//        stringList.addAll(set);
        System.out.println("set================"+set);
        System.out.println("list================"+stringList);
    }

 使用Java8的写法：

List unique = list.stream().distinct().collect(Collectors.toList());

 二、List中对象去重

 比如现在有一个 Person类:

public class Person {
    private Long id;

    private String name;

    public Person(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

 重写Person对象的equals()方法和hashCode()方法:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    Person person = (Person) o;

    if (!id.equals(person.id)) return false;
    return name.equals(person.name);

}

@Override
public int hashCode() {
    int result = id.hashCode();
    result = 31 * result + name.hashCode();
    return result;
}

 下面对象去重的代码：

Person p1 = new Person(1l, "jack");
Person p2 = new Person(3l, "jack chou");
Person p3 = new Person(2l, "tom");
Person p4 = new Person(4l, "hanson");
Person p5 = new Person(5l, "胶布虫");

List persons = Arrays.asList(p1, p2, p3, p4, p5, p5, p1, p2, p2);

List personList = new ArrayList<>();
// 去重
persons.stream().forEach(
    p -> {
        if (!personList.contains(p)) {
            personList.add(p);
        }
    }
);
System.out.println(personList);

三、根据对象的属性去重

 这个是重点部分了 

 实体类

package com.yzg.array;
public class Student {
    private int id;
    private String name;

    public Student() {
    }

    public Student(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

 去重实现

package com.yzg.array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.TreeSet;
import static java.util.Comparator.comparingLong;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;
public class StuArray {
    public static void main(String[] args) {

        Student s=new Student();
        s.setId(1);
        s.setName("小明");

        Student s1=new Student();
        s1.setId(2);
        s1.setName("小红");

        Student s2=new Student();
        s2.setId(2);
        s2.setName("小甘");

        List stu= Arrays.asList(s,s1,s2);

        for (Student t: stu
             ) {
            System.out.println(t.toString());
        }

        //去重
        List list=stu.stream().collect(
                collectingAndThen(
                        toCollection(() -> new TreeSet<>(comparingLong(Student::getId))), ArrayList::new));

        System.out.println("移除后的数组=========================");
        for (Student t: list
        ) {
            System.out.println(t.toString());
        }
    }
}

 换成对应的实体类，和需要去重的属性即可

import java.util.TreeSet;
import static java.util.Comparator.comparingLong;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;

//去重
List list=stu.stream().collect(
        collectingAndThen(
                toCollection(() -> new TreeSet<>(comparingLong(Student::getId))), ArrayList::new));