从List集合中删除指定元素

从List集合中删除指定元素的几种方式

最近在使用这个操作的时候搜索了一下网上的文章，发现有些能用有些不能用，
由于使用之前没有做详细的测试，导致程序bug，今天抽空做了一下总结和测试。

package com.arthas.testDemo.demo;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

/**
* @date 2021/8/24 15:15
*/
public class ListRemove {
   class User {
       public String name;
       public Integer age;
       public String classNo;

       @Override
       public String toString() {
           return "User{" +
                   "name='" + name + '\'' +
                   ", age=" + age +
                   ", classNo='" + classNo + '\'' +
                   '}';
       }
   }

   public List<User> getUserList(int num) {
       List<User> list = new ArrayList<>();
       for (int i = 0; i < num; i++) {
           User u = new User();
           u.age = i + 10;
           u.name = "a" + i;
           u.classNo = String.valueOf(i);
           list.add(u);
       }
       return list;
   }

   public static void main(String[] args) {
       ListRemove listRemove = new ListRemove();
       //数据生成
       List<User> userList = listRemove.getUserList(5);
       System.out.println("原数据：" + Arrays.toString(userList.toArray()));
       //测试过滤掉 name = a2 或者 classNo = 4
       //方法一：Iterator删除
       List<User> iteratorList = new ArrayList<>(userList);
       Iterator<User> iterator = iteratorList.iterator();
       while (iterator.hasNext()) {
           User next = iterator.next();
           if ("a2".equals(next.name) || "4".equals(next.classNo)) {
               iterator.remove();
           }
       }
       System.out.println("Iterator删除:" + Arrays.toString(iteratorList.toArray()));

       //方法二：removeIf删除
       List<User> removeIfList = new ArrayList<>(userList);
       removeIfList.removeIf(next -> "a2".equals(next.name) || "4".equals(next.classNo));
       System.out.println("removeIf删除:" + Arrays.toString(removeIfList.toArray()));

       //方法三：使用stream    注意：此方法测试未达到预期结果， 不适用
       List<User> streamList = new ArrayList<>(userList);
       streamList.stream().findFirst().map(e -> {
           if ("a2".equals(e.name) || "4".equals(e.classNo)) {
               streamList.remove(e);
           }
           return e;
       });
       System.out.println("stream删除:" + Arrays.toString(streamList.toArray()));

       //方法四：使用stream+索引   注意：此方法测试未达到预期结果，不适用
       List<User> streamIndexList = new ArrayList<>(userList);
       IntStream.range(0, streamIndexList.size()).filter(i ->
               "a2".equals(streamIndexList.get(i).name) || "4".equals(streamIndexList.get(i).classNo)).
               boxed().findFirst().map(i -> streamIndexList.remove((int) i));
       System.out.println("stream+index删除:" + Arrays.toString(streamIndexList.toArray()));

       //方法三：使用filter
       List<User> filterList = new ArrayList<>(userList);
       filterList = filterList.stream().filter(e -> !"a2".equals(e.name) && !"4".equals(e.classNo)).collect(Collectors.toList());
       System.out.println("filter删除:" + Arrays.toString(filterList.toArray()));

       System.out.println("原数据：" + Arrays.toString(userList.toArray()));
   }
}

生成结果如下：

原数据：[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a2', age=12, classNo='2'}, User{name='a3', age=13, classNo='3'}, User{name='a4', age=14, classNo='4'}]
Iterator删除:[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a3', age=13, classNo='3'}]
removeIf删除:[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a3', age=13, classNo='3'}]
stream删除:[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a2', age=12, classNo='2'}, User{name='a3', age=13, classNo='3'}, User{name='a4', age=14, classNo='4'}]
stream+index删除:[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a3', age=13, classNo='3'}, User{name='a4', age=14, classNo='4'}]
filter删除:[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a3', age=13, classNo='3'}]
原数据：[User{name='a0', age=10, classNo='0'}, User{name='a1', age=11, classNo='1'}, User{name='a2', age=12, classNo='2'}, User{name='a3', age=13, classNo='3'}, User{name='a4', age=14, classNo='4'}]

Process finished with exit code 0

测试结果表明，使用Iterator, removeIf, filter均能正常实现这个功能，而网上多篇文章提供的strem.findFirst操作，stream+索引操作在测试中没有达到预期结果；不知道当时的作者在完成文章时是如何实现预期结果的，仓促完成，不足之处请指正！谢谢！