java多线程 同步-金沙1005

//不安全的买票
	//线程不安全，有负数或者多人买到同一张票
public class unsafebuyticket { 
   
	public static void main(string[] args) { 
   
		buyticket buyticket = new buyticket();
		new thread(buyticket,"苦逼的我").start();
		new thread(buyticket,"牛逼的你们").start();
		new thread(buyticket,"可恶的黄牛党").start();
	}
}
class buyticket implements runnable{ 
   
	//票数
	private int num = 10;
	private boolean flag = true;//判断是否停止线程 thread的stop已经废弃不建议使用
	@override
	public void run() { 
   
		//买票
		while (flag){ 
   
			buy();
		}
	}
	public void buy(){ 
   
		//判断是否有票
		if(num<=0){ 
   
			flag = false;
			return ;
		}
		try { 
   
			//模拟延时（放大问题的发生性）
			thread.sleep(100);
		} catch (interruptedexception e) { 
   
			e.printstacktrace();
		}
		//买票
		system.out.println(thread.currentthread().getname()"买到了第"num--"票");
	}
}

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解决方法：通过关键字synchronized来设置同步锁 在buy()方法前面添加synchronized关键字来锁定这个方法

public synchronized void buy(){ 
   
	//判断是否有票
	if(num<=0){ 
   
		flag = false;
		return ;
	}
	try { 
   
		//模拟延时（放大问题的发生性）
		thread.sleep(100);
	} catch (interruptedexception e) { 
   
		e.printstacktrace();
	}
	//买票
	system.out.println(thread.currentthread().getname()"买到了第"num--"票");
}

如上图添加了synchronized关键字后就避免了多人抢到同一张票的情况，也避免了在没有票的情况下继续出票的情况

//不安全的取钱
//两个人去银行取钱，账户
public class unsafebank { 

public static void main(string[] args) { 

account account = new account(100, "结婚基金");
drawing you = new drawing(account, 50, "你");
drawing grilfriend = new drawing(account, 100, "grilfriend");
grilfriend.start();
you.start();
}
}
//账户
class account{ 

int money;//余额
string name;//卡名称
public account(int money, string name) { 

this.money = money;
this.name = name;
}
}
//银行：模拟取钱
class  drawing extends thread{ 

account account;//账户
int drawingmoney;//取多少钱
int nowmoney;//现在手里有多少钱
public drawing(account account,int drawingmoney,string name){ 

super(name);
this.account = account;
this.drawingmoney = drawingmoney;
}
@override
public void run() { 

//判断账户里面有没有钱
if(account.money-drawingmoney<0){ 

system.out.println(thread.currentthread().getname()"钱不够了，取不了");
return;
}
//sleep 放大问题的发生性
try { 

thread.sleep(1000);
} catch (interruptedexception e) { 

e.printstacktrace();
}
//卡内余额 = 余额 - 你取的钱
account.money = account.money - drawingmoney;
//你手上的钱
nowmoney = nowmoney  drawingmoney;
system.out.println(account.name "余额为："account.money);
//hread.currentthread().getname() = this.getname()；
system.out.println(this.getname()"手里的钱"nowmoney);
}
}

上述的问题就是你去50万，你老婆去100万，结果银行还倒贴了50万

解决方法：给银行账户添加锁 synchronized(account)

@override
public void run() { 

synchronized (account){ 

//判断账户里面有没有钱
if(account.money-drawingmoney<0){ 

system.out.println(thread.currentthread().getname()"钱不够了，取不了");
return;
}
//sleep 放大问题的发生性
try { 

thread.sleep(1000);
} catch (interruptedexception e) { 

e.printstacktrace();
}
//卡内余额 = 余额 - 你取的钱
account.money = account.money - drawingmoney;
//你手上的钱
nowmoney = nowmoney  drawingmoney;
system.out.println(account.name "余额为："account.money);
//hread.currentthread().getname() = this.getname()；
system.out.println(this.getname()"手里的钱"nowmoney);
}
}

只要有一个人取完后另一个人就会因为余额不足取不了，保证了线程的安全