java.util.concurrent.CopyOnWriteArrayList

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.CopyOnWriteArrayList;
 
public class TestCalc {
    /**
     *read 
     */
    private static class ReadTask implements Runnable {
        List<String> list;
 
        public ReadTask(List<String> list) {
            this.list = list;
        }
 
        public void run() {
            for (String str : list) {
                System.out.println(str);
            }
        }
    }
    /**
     *write
     *
     */
    private static class WriteTask implements Runnable {
        List<String> list;
        int index;
 
        public WriteTask(List<String> list, int index) {
            this.list = list;
            this.index = index;
        }
 
        public void run() {
            list.remove(index);
            list.add(index, "write_" + index);
        }
    }
 
    public void run() {
        final int NUM = 10;
         //List<String> list = new ArrayList<String>(); //java.util.ConcurrentModificationException
         CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();
        for (int i = 0; i < NUM; i++) {
            list.add("main_" + i);
        }
        ExecutorService executorService = Executors.newFixedThreadPool(NUM);
        for (int i = 0; i < NUM; i++) {
            executorService.execute(new ReadTask(list));
            executorService.execute(new WriteTask(list, i));
        }
        executorService.shutdown();
    }
 
    public static void main(String[] args) {
        new TestCalc().run();
    }
}

/*

 //List<String> list = new ArrayList<String>(); 
Exception in thread "pool-1-thread-11" java.util.ConcurrentModificationException

        at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
        at java.util.ArrayList$Itr.next(Unknown Source)
        at TestCalc$ReadTask.run(TestCalc.java:19)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
*/