java多线程编程，2交替输出数字和字母

mark一下，不停的看看notify和wait的没有理解

class Printer
{
    int index=0;
    //输出奇数
    public synchronized void printA(int a)
    {
        while(index%2==0)
        {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        index++;
        System.out.println(a);
        notify();
        
    }
    public  synchronized void printB(char b)
    {
        while(index%2!=0)
        {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        index++;
        System.out.println(b);
        notify();
        
    }
    
}
public class 多线程1 {
    public static void main(String args[])
    {
        Printer p=new Printer();
        Thread t1=new Thread(new A(p));
        Thread t2=new Thread(new B(p));
        t1.start();
        t2.start();
        
        
        
        
    }
    

}

class A implements Runnable
{
    Printer p=null;
    public A(Printer p)
    {
        this.p=p;
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub
        for(int i=1;i<=26;i++)
        {
        p.printA(i);
        }
        
        
    }
    
    
}
class B implements Runnable
{
    Printer p=null;
    public B(Printer p)
    {
        this.p=p;
    }

    public void run() {
        // TODO Auto-generated method stub
        for(char c='a';c<='z';c++)
        {
        p.printB(c);
        }
        
        
    }
    
    
}