list简单去重代码

文章目录

• 记录一下集合去重的几种方法

• stream去重，推荐，使用java8的stream api的distinct方法去重
• LinkedHashSet去重，推荐，返回的数据顺序不变。可以使用hashset，但是不保证顺序。可以根据要求来。
• Collection的的contains方法进行判断。可以使用list（有序）也可以使用set（无序）。
• 双重for删除，不方便看。
• main代码：

记录一下集合去重的几种方法

stream去重，推荐，使用java8的stream api的distinct方法去重

public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(Arrays.asList("a","a","b","b","b","c"));
        System.out.println(JSONObject.toJSONString(list));
        repeatRemovetest1(list);
    }


    public static void repeatRemovetest1(List<String> list) {
        List<String> listWithoutDuplicates = list.stream().distinct().collect(Collectors.toList());
        System.out.println(listWithoutDuplicates);
    }

LinkedHashSet去重，推荐，返回的数据顺序不变。可以使用hashset，但是不保证顺序。可以根据要求来。

public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(Arrays.asList("a","a","b","b","b","c"));
        System.out.println(JSONObject.toJSONString(list));
        repeatRemovetest2(list);
    }

  public static void repeatRemovetest2(List<String> list) {
        LinkedHashSet<String> linkSet = new LinkedHashSet<>(list);
        ArrayList<String> listWithoutDuplicates = new ArrayList<>(linkSet);
        System.out.println(listWithoutDuplicates);
    }

Collection的的contains方法进行判断。可以使用list（有序）也可以使用set（无序）。

public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(Arrays.asList("a","a","b","b","b","c"));
        System.out.println(JSONObject.toJSONString(list));
        repeatRemovetest3(list);
    }

    public static void repeatRemovetest3(List<String> list) {
        HashSet<Object> sets = new HashSet<>();
        ArrayList<String> temList = new ArrayList<>(list.size());
        for (String s : list) {
            if (!temList.contains(s)) {
                temList.add(s);
            }
        }
        System.out.println(temList);
    }

双重for删除，不方便看。

public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(Arrays.asList("a", "a", "b", "b", "b", "c"));
        System.out.println(JSONObject.toJSONString(list));
        repeatRemovetest4(list);
    }
    
 public static void repeatRemovetest4(List<String> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = 0; j < list.size(); j++) {
                if (i != j && list.get(i) == list.get(j)) {
                    list.remove(list.get(j));
                }
            }
        }
        System.out.println(list);
    }

main代码：

import com.alibaba.fastjson.JSONObject;

import java.util.*;
import java.util.stream.Collectors;

public class RepeatRemoveTest {

    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>(Arrays.asList("a", "a", "b", "b", "b", "c"));
        System.out.println(JSONObject.toJSONString(list));
        repeatRemovetest4(list);
    }


    public static void repeatRemovetest1(List<String> list) {
        List<String> listWithoutDuplicates = list.stream().distinct().collect(Collectors.toList());
        System.out.println(listWithoutDuplicates);
    }

    public static void repeatRemovetest2(List<String> list) {
        LinkedHashSet<String> linkSet = new LinkedHashSet<>(list);
        ArrayList<String> listWithoutDuplicates = new ArrayList<>(linkSet);
        System.out.println(listWithoutDuplicates);
    }

    public static void repeatRemovetest3(List<String> list) {
        HashSet<Object> objects = new HashSet<>();
        ArrayList<String> temList = new ArrayList<>(list.size());
        for (String s : list) {
            if (!temList.contains(s)) {
                temList.add(s);
            }
        }
        System.out.println(temList);
    }

    public static void repeatRemovetest4(List<String> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = 0; j < list.size(); j++) {
                if (i != j && list.get(i) == list.get(j)) {
                    list.remove(list.get(j));
                }
            }
        }
        System.out.println(list);
    }

}