线程同步 synchronized

多线程操作统一资源（临界资源）时，需要同步机制；

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队列和锁

1. 不安全买票

public class UnsafeBuyTicket {
	public static void main (String[] args) {
		BuyTicket station =new BuyTicket();
		new Thread(station,"我").start();
		new Thread(station,"你").start();
		new Thread(station,"该死的黄牛").start();
		
	}

}
class BuyTicket implements Runnable{

	private int ticketNums=10;
	boolean flag= true;
	
	@Override
	public void run() {
		// 买票
		while(flag) {
			try {
				buy();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
	
	private void buy() throws InterruptedException {
		//判断是否有票
		if(ticketNums<=0) {
			flag=false;
			return;
		}
		
		//模拟延时
		Thread.sleep(100);
		//买票
		System.out.println(Thread.currentThread().getName()+"拿到了"+ticketNums--);
	}
	
}

2. 不安全的取钱（银行）

   package synchronize;
   
   
   //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 girlfriend =new Drawing(account,100,"girlfriend");
   		
   		you.start();
   		girlfriend.start();
   	}
   }
   
   //账户
   class Account{
   	int money;//余额
   	String name;//卡名
   	 public Account (int money, String name) {
   		 this.money=money;
   		 this.name=name;
   	 }
   
   }
   
   
   //银行模拟取款
   class Drawing extends Thread{
   	Account account;//账户
   	int drawingMoney;//取多少钱
   	int nowMoney;//手中有多少钱
   	
   	public Drawing(Account account,int drawingMoney,String name) {//有参构造器
   		super(name);//给线程名字
   		this.account=account;
   		this.drawingMoney=drawingMoney;
   		
   	}
   	
   	
   	//取钱方法
   	public void run() {
   		//先判断有没有钱
   		if (account.money-drawingMoney<0) {
   			System.out.println(Thread.currentThread().getName()+"钱不够，取不出来！");
   			return;
   		}
   		
   		try {//增加延时，放大问题发生性
   			Thread.sleep(1000);
   		} catch (InterruptedException e) {
   			// TODO Auto-generated catch block
   			e.printStackTrace();
   		}
   		//卡内余额=余额-取出的钱；
   		account.money-=drawingMoney;
   		//手里的钱
   		nowMoney += drawingMoney;
   		
   		System.out.println(account.name+"余额为："+account.money);
   		System.out.println(this.getName()+"手里的钱为："+nowMoney);
   		
   	}
   }
   

3. 线程不完全的集合

   import java.util.List;
   import java.util.ArrayList;
   //线程不安全的集合
   public class MyTest {
       public static void main(String[] args) throws InterruptedException {
           List<String> list = new ArrayList<>();
           for (int i = 0; i < 10000; i++) {
               new Thread(()->{
                   list.add(Thread.currentThread().getName()
                   );
               }).start();
           }
           Thread.sleep(2000);
           System.out.println(list.size());
       }
   }