list的去重方式

List的去重方式

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 + "]");
}

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 + '\'' +
            '}';
}
}

jdk1.8中去重方式

1、list.stream().distinct()
2、双层循环
Set set = new HashSet<>(list);