写2个线程，一个打印1-52，一个打印A-Z，打印顺序是12A34B。。。（采用同步代码块和同步方法两种同步方法）

1.同步方法

package Synchronized;
/************************************同步方法****************************************/
public class PrintTest {
	public static void main(String[] args)
	{
		Print p = new Print();
		Thread t1 = new PrintNumber(p);
		Thread t2 = new PrintWord(p);
		t1.start();
		t2.start();
	}
}

class PrintNumber extends Thread {//打印数字线程
	private Print p;

	public PrintNumber(Print p) {
		this.p = p;
	}

	public void run() {
		for (int i = 0; i < 26; i++) {
			p.printNumber();
		}
	}
}

class PrintWord extends Thread {//打印字母线程
	private Print p;

	public PrintWord(Print p) {
		this.p = p;
	}

	public void run() {
		for (int i = 0; i < 26; i++) {
			p.printWord();
		}
	}
}

class Print {             //同步监视器是Print类
	private int i = 1;
	private char j = 'A';

	public Print() {
	}

	public synchronized void printNumber() {//同步方法
		System.out.print(String.valueOf(i) + String.valueOf(i + 1));
		i += 2;
		notifyAll();      //先唤醒其他进程，再阻塞本进程，如果顺序颠倒了，进程阻塞后不能再唤醒其他进程
		try {
			wait();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	public synchronized void printWord() {
		System.out.print(j);
		j++;
		notifyAll();
		try
		{
			if (j <= 'Z')//输出Z之后就不用再等待了。
			{

				wait();
			}
		} 
		catch (InterruptedException e) {
			e.printStackTrace();
		}

	}
}

 2.同步代码块package threaddemo;

/**
 * <写两个线程，一个线程打印1-52，另一个线程打印字母A-Z。打印 顺序为12A34B56C……5152Z>
 * 
 */
/*****************************************同步代码块*********************************************/
public class ThreadDemo
{
    // 测试
    public static void main(String[] args) throws Exception
    {
        Object obj = new Object();
        // 启动两个线程
        Thread1 t1 = new Thread1(obj);
        
        Thread2 t2 = new Thread2(obj);
        
        t1.start();
        t2.start();
    }
    
}

// 一个线程打印1-52
class Thread1 extends Thread
{
    private Object obj;
    
    public Thread1(Object obj)
    {
        this.obj = obj;
    }
    
    public void run()
    {
        synchronized (obj)
        {
            // 打印1-52
            for (int i = 1; i < 53; i++)
            {
                System.out.print(i + " ");
                if (i % 2 == 0)
                {
                    // 不能忘了 唤醒其它线程
                    obj.notifyAll();
                    try
                    {
                        obj.wait();
                    }
                    catch (InterruptedException e)
                    {
                        e.printStackTrace();
                    }
                }
            }
        }
        
    }
    
}

// 另一个线程打印字母A-Z
class Thread2 extends Thread
{
    private Object obj;
    
    public Thread2(Object obj)
    {
        this.obj = obj;
    }
    
    public void run()
    {
        synchronized (obj)             //同步监视器是obj类，同步代码块是写在run方法里面的。
        {
            // 打印A-Z
            for (int i = 0; i < 26; i++)
            {
                System.out.print((char)('A' + i) + " ");
                // 不能忘了 唤醒其它线程
                obj.notifyAll();
                try
                {
                    // 最后一个就不要等了
                    if (i != 25)
                    {
                        obj.wait();
                    }
                }
                catch (InterruptedException e)
                {
                    e.printStackTrace();
                }
                
            }
            
        }
    }
    
}

 下面是我后来写的。自习区分一下，因为主程序只有两个线程相互交替，所以是没有必要设置flag的。只有很多进程交互的时候，才有必要设置flag，并且我是通过flag来判断切换进程的，所以循环次数是52次，而不是26次。

public class test1 
{
	public static void main(String[] args) {
		Print p = new Print();
		new PrintNumber(p).start();
		new PrintWord(p).start();
	}
}
class Print
{
	private boolean flag = false;
	public int num = 1;
	public char chr = 'A';
	public synchronized void printNumber()
	{
		try
		{
			if(flag)
			{
				if(num <= 52)
				{
					wait();
				}
			}
			else
			{
				System.out.print(num);
				System.out.print(num + 1);
				num += 2;
				flag = true;
				notify();
			}
		}
		catch(InterruptedException ie)
		{
			ie.printStackTrace();
		}
	}
	
	public synchronized void printWord()
	{
		try
		{
			if(!flag)
			{
				if(chr <= 'Z')
				{
					wait();
				}
			}
			else
			{
				System.out.print(chr);
				chr += 1;
				flag = false;
				notify();
			}
		}
		catch(InterruptedException ie)
		{
			ie.printStackTrace();
		}
	}
}
class PrintNumber extends Thread
{
	Print p;
	PrintNumber(Print p)
	{
		this.p = p;
	}
	public void run()
	{
		for(int i = 0; i < 52; i ++)
		{
			p.printNumber();
		}
	}
}
class PrintWord extends Thread
{
	Print p;
	PrintWord(Print p)
	{
		this.p = p;
	}
	public void run()
	{
		for(int i = 0; i < 52; i ++)
		{
			p.printWord();
		}
	}
}

 实现Runnable接口

public class test2 {
	public static void main(String[] args) {
		Print p = new Print();
		new Thread(new Runnable() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				for(int i = 0; i < 26; i ++)
				{
					p.printNum();
				}
			}
		}).start();
		new Thread(new Runnable() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				for(int i = 0; i < 26; i ++)
				{
					p.printWord();
				}
			}
		}).start();
	}
}
class Print
{
	char chr = 'A';
	int num = 1;
	public synchronized void printNum()
	{
		System.out.print(num);
		System.out.print(num + 1);
		num += 2;
		notify();
		try{
			wait();
		}
		catch(InterruptedException ie)
		{
			ie.printStackTrace();
		}
				
	}
	public synchronized void printWord()
	{
		System.out.print(chr);
		chr += 1;
		notify();
		try{
			if(chr <= 'Z')
			wait();
		}
		catch(InterruptedException ie)
		{
			ie.printStackTrace();
		}
	}
}