List集合的去重

 

一、String去重：  
  
//set集合去重，不改变原有的顺序
    public static void pastLeep1(List<String> list){
        System.out.println("list = [" + list.toString() + "]");
        List<String> listNew=new ArrayList<>();
        Set set=new HashSet();
        for (String str:list) {
            if(set.add(str)){
                listNew.add(str);
            }
        }
        System.out.println("listNew = [" + listNew.toString() + "]");
    }

//遍历后判断赋给另一个list集合
    public static void pastLeep2(List<String> list){
        System.out.println("list = [" + list.toString() + "]");
        List<String> listNew=new ArrayList<>();
        for (String str:list) {
            if(!listNew.contains(str)){
                listNew.add(str);
            }
        }
        System.out.println("listNew = [" + listNew.toString() + "]");
    }

//set去重
    public static void pastLeep3(List<String> list){
        System.out.println("list = [" + list + "]");
        Set set = new HashSet();
        List<String> listNew=new ArrayList<>();
        set.addAll(list);
        listNew.addAll(set);
        System.out.println("listNew = [" + listNew + "]");
    }

    //set去重（缩减为一行）
    public static void pastLeep4(List<String> list){
        System.out.println("list = [" + list + "]");
        List<String> listNew=new ArrayList<>(new HashSet(list));
        System.out.println("listNew = [" + listNew + "]");
    }

    //去重并按自然顺序排序
    public static void pastLeep5(List<String> list){
        System.out.println("list = [" + list + "]");
        List<String> listNew=new ArrayList<>(new TreeSet<String>(list));
        System.out.println("listNew = [" + listNew + "]");
    }


二、对象去重方法：

package com.hcycom.iams.ncolog;

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

public class Test {

    public static void main(String[] args) {
        Data data1 = new Data(1,"aaaa");
        Data data2 = new Data(2,"dddd");
        Data data3 = new Data(1,"vvvv");
        Data data4 = new Data(4,"rrrr");
        Data data5 = new Data(1,"ssss");
        List<Data> list = Arrays.asList(data1,data2,data3,data4,data5);
        List<Data> l = test2(list);
        System.out.println(Arrays.toString(l.toArray()));

    }

    //对象去重
    public static List<Data> test2(List<Data> list){
        List<Data> unique = list.stream().collect(
                collectingAndThen(
                        toCollection(() -> new TreeSet<>(comparingLong(Data::getId))), ArrayList::new)
        );
        return unique;
    }
}

// 实体对象
class Data{

    private int id;
    private String name;

    public Data(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 "Data{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}