List去重、排序详解编程语言

package com; 
 
import lombok.Data; 
import lombok.extern.slf4j.Slf4j; 
import org.junit.Test; 
import java.util.*; 
import java.util.stream.Collectors; 
 
@Slf4j 
public class JunitTest{
 
    //排序 
    @Test 
    public void sort(){ 
        List<Integer> lists = Arrays.asList(1,1,2,3); 
        // 升序 
        lists.sort(Comparator.comparing(Integer::intValue)); 
        lists.stream().sorted().collect(Collectors.toList()); 
 
        // 降序 
        lists.sort(Comparator.comparing(Integer::intValue).reversed()); 
        lists.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList()); 
 
        //集合对象排序 
        List<User> list = new ArrayList<User>(); 
        list.add(new User(5,"zhagnsan",18)); 
        list.add(new User(4,"libai",19)); 
        list.add(new User(1,"wangwu",22)); 
        list.add(new User(2,"lihua",11)); 
        //根据ID排序-1 
        list.sort(Comparator.comparing(User::getId)); 
        //根据ID排序-2 
        Collections.sort(list,new Comparator<User>(){ 
            @Override 
            public int compare(User o1, User o2) { 
                return o1.getId() - o2.getId(); 
            } 
        }); 
    } 
 
    //去重 
    @Test 
    public void removal() { 
        //1.使用LinkedHashSet删除arraylist中的重复数据 
        //删除重复数据 
        //保持添加到其中的数据的顺序 
        ArrayList<Integer> arrayList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3)); 
        System.out.println(arrayList); 
 
        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>(arrayList); 
        ArrayList<Integer> integers = new ArrayList<>(linkedHashSet); 
        System.out.println(integers); 
 
        //2.使用java8新特性stream进行List去重 
        //java 8 stream api。使用steam的distinct()方法返回一个由不同数据组成的流，通过对象的equals（）方法进行比较。 
        //收集所有区域数据List使用Collectors.toList() 
        arrayList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3)); 
        System.out.println(arrayList); 
        List<Integer> integerList = arrayList.stream().distinct().collect(Collectors.toList()); 
        System.out.println(integerList); 
 
        //3.用HashSet不能添加重复数据的特性 
        // 由于HashSet不能保证添加顺序，所以只能作为判断条件保证顺序： 
        arrayList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3)); 
        HashSet<Integer> set = new HashSet<Integer>(arrayList.size()); 
        List<Integer> result = new ArrayList<Integer>(arrayList.size()); 
        for (Integer str : arrayList) { 
            if (set.add(str)) { 
                result.add(str); 
            } 
        } 
        arrayList.clear(); 
        arrayList.addAll(result); 
 
        //4.用List的contains方法循环遍历,重新排序,只添加一次数据,避免重复 
        arrayList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3)); 
        List<Integer> integerArrayList = new ArrayList<Integer>(arrayList.size()); 
        for (Integer integer : integerArrayList) { 
            if (!result.contains(integer)) { 
                result.add(integer); 
            } 
        } 
        arrayList.clear(); 
        arrayList.addAll(result); 
 
        //5.双重for循环去重 
        arrayList = new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3, 3)); 
        for (int i = 0; i < arrayList.size(); i++) { 
            for (int j = 0; j < arrayList.size(); j++) { 
                if (i != j && arrayList.get(i) == arrayList.get(j)) { 
                    arrayList.remove(arrayList.get(j)); 
                } 
            } 
        } 
 
        //6.根据年龄的性别去重 
        List<User> list = new ArrayList<User>(); 
        list.add(new User(5,"zhagnsan",18)); 
        list.add(new User(4,"libai",19)); 
        list.add(new User(1,"wangwu",18)); 
        list.add(new User(2,"lihua",11)); 
        ArrayList<User> collect = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection( 
                () -> new TreeSet<>(Comparator.comparing(User::getAge))), ArrayList::new)); 
        System.out.println(collect); 
 
    }
 
    @Data 
    class User{ 
        private int id; 
        private String name; 
        private int age; 
 
        private User(int id,String name,int age){ 
            this.id = id; 
            this.name = name; 
            this.age = age; 
 
        } 
    } 
}