java多线程——Thread加锁的3种方法（以售票为例）

方法1：
在唯一的对象中 声明一个属性 一定不能是基本数据类型 一般是Object类型
使用synchronized代码块 括号中必须放这个锁 然后将代码放到synchronized代码块中
代码就变成 线程安全的代码 整个代码资源就会同步

package ls190521;

public class SellTicket implements Runnable
{

	private int ticket=100;
	private Object lock=new Object();
	public void run()
	{
		synchronized (lock)
		{
			for(int i=1;i<=30&&ticket>0;i++)
			{
				System.out.println(Thread.currentThread().getName()+"当前还剩"+ticket+"张票");
				ticket--;
			}
		}
	}
	public static void main(String[] args)
	{
		SellTicket sellticket=new SellTicket();
		Thread thread1=new Thread(sellticket);
		Thread thread2=new Thread(sellticket);
		Thread thread3=new Thread(sellticket);
		Thread thread4=new Thread(sellticket);
		Thread thread5=new Thread(sellticket);
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
	}
}

或者把run方法改成：

public void run()
	{
		while(true)
		{
			synchronized (lock)
			{
				if(ticket<=0)
				{
					break;
				}
				System.out.println(Thread.currentThread().getName()+"当前还剩"+ticket+"张票");
				ticket--;
			}
		}
	}

运行结果：

方法2：
如果在run方法中调用其它的方法 其他类的方法要加锁 synchronized

package ls190521;

public class SellTicket implements Runnable
{

	private int ticket=100;
	private Object lock=new Object();
	public void run()
	{
		dosomthing();
	}
	public void dosomthing()
	{
		synchronized (lock)
		{
			for(int i=1;i<=30&&ticket>0;i++)
			{
				System.out.println(Thread.currentThread().getName()+"当前还剩"+ticket+"张票");
				ticket--;
			}
		}
	}
	public static void main(String[] args)
	{
		SellTicket sellticket=new SellTicket();
		Thread thread1=new Thread(sellticket);
		Thread thread2=new Thread(sellticket);
		Thread thread3=new Thread(sellticket);
		Thread thread4=new Thread(sellticket);
		Thread thread5=new Thread(sellticket);
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
	}
}

可以达到同样的效果
方法3：
如果当前使用的runabled接口 可以直接将自己作为锁 因为runabled接口的实现有且只有一个

package ls190521;

public class SellTicket implements Runnable
{

	private int ticket=100;
	public void run()
	{
		synchronized (this)
		{
			for(int i=1;i<=30&&ticket>0;i++)
			{
				System.out.println(Thread.currentThread().getName()+"当前还剩"+ticket+"张票");
				ticket--;
			}
		}
	}
	
		
	
	public static void main(String[] args)
	{
		SellTicket sellticket=new SellTicket();
		Thread thread1=new Thread(sellticket);
		Thread thread2=new Thread(sellticket);
		Thread thread3=new Thread(sellticket);
		Thread thread4=new Thread(sellticket);
		Thread thread5=new Thread(sellticket);
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
	}
}