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; 
} 
} 
}