1、ArrayList线程不安全；CopyOnWriteArrayList线程安全
package concurrent;

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

/**
 * Auth: zhouhongliang
 * Date：2019/8/1
 * CopyOnWriteArrayList 替代 ArrayList
 */
public class CopyOnWriteArrayListDemo {
    public static void main(String[] args) {
        List<Integer> list = new CopyOnWriteArrayList<>();
        //List<Integer> list = new CopyOnWriteArrayList<>();
        for (int i=0;i<1000;i++){
            list.add(i);
        }
        Iterator iterator = list.iterator();
        while(iterator.hasNext()){
            list.remove(iterator.next());
        }
        System.out.println(list);
    }
}

2、HashMap线程不安全；HashTable synchronize线程安全、```
ConcurrentHashMap采用”分段锁”线程安全；
package concurrent;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**

• Auth: zhouhongliang
• Date：2019/8/1
  */
  public class ConcurrentHashMapDemo {
  public static void main(String[] args) throws InterruptedException {
  Map map = new HashMap();//线程不安全
  //Map map = new Hashtable();//线程安全
  //Map map = new ConcurrentHashMap();//线程安全
  ExecutorService executorService = Executors.newCachedThreadPool();
  CountDownLatch countDownLatch = new CountDownLatch(10000);
  for (int i=0;i<10000;i++){
  final Integer index = i;
  executorService.execute(()->{
  map.put(index,index);
  countDownLatch.countDown();
  });
  }
  countDownLatch.await();
  System.out.println(map.size());
  }
  }