java 5 ReadWriteLock

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
 
public class ReadWriteLockTest
{
    private static List<String> list = new ArrayList<String>();
    public static void main(String[] args)
    {
        for(int i = 0; i < 10; i++)
        {
            list.add("init - " + i);
        }
        new Thread(new Runnable()
        {
            public void run()
            {
                try
                {
                    ReadWriteLockTest.add();
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        }).start();
        new Thread(new Runnable()
        {
            public void run()
            {
                try
                {
                    ReadWriteLockTest.get();
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        }).start();
    }
 
    private static ReadWriteLock lock = new ReentrantReadWriteLock();
    private static void add() throws Exception
    {
        for(int i = 0; i < 10; i++)
        {
            lock.writeLock().lock();
            list.add("add-" + i);
            lock.writeLock().unlock();
            System.out.println("add " + i);
            Thread.sleep(500);
        }
    }
 
    private static void get() throws Exception
    {
        lock.readLock().lock();
        for(String str : list)
        {
            System.out.println("get- " + str);
            Thread.sleep(500);
        }
        lock.readLock().unlock();
    }
}

上面有2个线程同时对list变量读写，如果不使用读写锁，则程序会抛出异常。

多个读锁不互斥，读锁也写锁互斥，写锁与写锁互斥。