不正确的访问共享资源

看下面一段代码，这段代码采用了模板设计模式

public abstract class IntGenerator {
         private volatile boolean canceled=false;

	public abstract int next();

	public void cancel()
	{                                                                           this.canceled=false;
	}

	public boolean isCanceled()
	{
	      return this.canceled;
	}


}

========================
//创建一个偶数生成类

public class EvenGenerator extends IntGenerator{

	private int currentEvenValue=0;

	@Override
	public int next() {
		// TODO Auto-generated method stub
		++currentEvenValue;
		++currentEvenValue;

		return currentEvenValue;
	}

	public static void main(String[] args)
	{
		EvenChecker.test(new EvenGenerator());
	}


}

===========================
创建一个测试类，启动10个线程，查看是否正确的访问资源

public class EvenChecker implements Runnable{
	private IntGenerator generator;
	private final int id;

	public EvenChecker(IntGenerator generator,int id) {
		// TODO Auto-generated constructor stub
		this.generator=generator;
		this.id=id;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		while(!generator.isCanceled())
		{
			int val=generator.next();
			if(val%2!=0)
			{
				System.out.println(val+ " is not even!");

generator.cancel();//直到找到奇数时停止
			}
			else
			{
				//System.out.println(val+" is even!");
			}
		}

	}



	public static void test(IntGenerator gp,int count)
	{

		System.out.println("Press Ctrl+C to Exit");
		ExecutorService exec=Executors.newCachedThreadPool();
		for(int i=0;i<count;i++)
			exec.execute(new EvenChecker(gp,i));
	}


	public static void test(IntGenerator gp)
	{
		test(gp,10);
	}




}

//测试的结果是能打印出很多奇数，访问资源出错的原因是：next()方法本身不是原子方法，可能在一个线程对它进行第一个++操作之后，第二个线程已经取到它的值了