Java如何解决ArrayList的并发问题

import java.util.ArrayList;
import java.util.List;

public class ArrayListConcurrencyExample {
    public static void main(String[] args) {
        List<Integer> arrayList = new ArrayList<>();

        // 创建并启动多个线程，同时向ArrayList添加元素
        Runnable addTask = () -> {
            for (int i = 0; i < 1000; i++) {
                arrayList.add(i);
            }
        };

        Thread thread1 = new Thread(addTask);
        Thread thread2 = new Thread(addTask);

        thread1.start();
        thread2.start();

        try {
            thread1.join();
            thread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // 输出ArrayList的大小，不一定是预期的 2000 
        System.out.println("Size of arrayList: " + arrayList.size());
    }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;

public class ConcurrentModificationExample {
    public static void main(String[] args) {
        List<String> arrayList = new ArrayList<>();

        arrayList.add("Item1");
        arrayList.add("Item2");
        arrayList.add("Item3");

        // 获取迭代器
        Iterator<String> iterator = arrayList.iterator();

        // 开始迭代
        while (iterator.hasNext()) {
            String item = iterator.next();
            System.out.println(item);

            // 在迭代过程中尝试修改ArrayList的结构，会引发ConcurrentModificationException
            if (item.equals("Item2")) {
                arrayList.remove(item);
            }
        }
    }
}

List<String> synchronizedList = Collections.synchronizedList(new ArrayList<>());

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class SynchronizedListExample {
    public static void main(String[] args) {
        List<Integer> synchronizedList = Collections.synchronizedList(new ArrayList<>());

        Runnable addAndRemoveTask = () -> {
            for (int i = 0; i < 1000; i++) {
                synchronizedList.add(i);
                synchronizedList.remove(synchronizedList.size() - 1);
            }
        };

        Thread thread1 = new Thread(addAndRemoveTask);
        Thread thread2 = new Thread(addAndRemoveTask);

        thread1.start();
        thread2.start();

        try {
            thread1.join();
            thread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Size of synchronizedList: " + synchronizedList.size());
    }
}

List<String> list = new CopyOnWriteArrayList<>();

List<String> list = new ArrayList<>();

// 在需要修改list的地方加锁
synchronized (list) {
    list.add("item");
}