java之 ------ 多线程（交互线程）

1、运行结果不惟一，取决于线程调度

2、线程执行被打断时出现错误

3、线程互斥和临界区管理

1）操作系统对共享一个变量的若干线程进入各自临界区有以下3个调度原则：

2）一次至多一个线程能够在它的临界区内。

3）不能让一个线程无限地留在它的临界区内。

4）不能强迫一个线程无限地等待进入它的临界区。特别地，进入临界区的任一线程不能妨碍正等待进入的其他线程的进展。

4、同步语句   synchronized (对象)

同步方法  synchronized  方法声明   方法声明synchronized(this){  方法体  }

5、银行账户的存款取款线程

Account.c

package p25;

public class Account {
	private String name;//储户姓名
	private double balance;//账户余额

	public Account(String name) {
		this.name = name;
		this.balance = 0;
	}
	//查询余额
	public double balance() {
		return this.balance;
	}

	public String getName() {
		return this.name;
	}
	//存款操作
	public void put(double value) {
		if (value > 0) {
			this.balance += value;
		}
	}
	//取款操作
	public double get(double value) {
		if (value > 0) {
			if (value < this.balance) {//够取
				this.balance -= value;
			} else {
				value = this.balance;
				this.balance = 0;
			}
			return value;
		}
		return 0;
	}
}

class Save extends Thread {
	private Account account;
	private double value;

	public Save(Account account, double value) {
		this.account = account;
		this.value = value;
	}

	public void run() {
		synchronized (account) {//声明临界区，锁定当前account对象
			double howmuch = this.account.balance();//查看账户余额
			try {
				sleep(1);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			this.account.put(this.value);
			double howmuch2 = this.account.balance();//查看账户余额
			System.out.println(this.account.getName() + "账户: 现有" + howmuch
					+ ",存入" + this.value + ",余额为" + howmuch2);
		}
	}
}

class Fetch extends Thread {
	private Account account;
	private double value;

	public Fetch(Account account, double value) {
		this.account = account;
		this.value = value;
	}

	public void run() {
		synchronized (account) {
			double howmuch = this.account.balance();
			try {
				sleep(1);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			double v = this.account.get(this.value);
			double howmuch2 = this.account.balance();
			System.out.println(this.account.getName() + "账户: 现有" + howmuch
					+ ",取出" + v + ",余额为" + howmuch2);
		}
	}
}

class Func extends Thread {
	private Account account;
	private double value;

	public Func(Account account, double value) {
		this.account = account;
		this.value = value;
	}

	public void run() {
		fun();
	}

	synchronized void fun(){
		double howmuch = this.account.balance();
		try {
			sleep(1);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		this.account.put(this.value);
		double v = this.account.get(this.value);
		double howmuch2 = this.account.balance();
		System.out.println(this.account.getName() + "账户: 现有" + howmuch + ",取出"
				+ v + ",余额为" + howmuch2);
	}

}

Bank.c

package p25;

public class Bank {

	public static void main(String[] args) {
		Account wang = new Account("wang");
		(new Save(wang,100)).start();
		(new Save(wang,200)).start();
		(new Fetch(wang,100)).start();

		Account li=new Account("li");
		(new Save(li,300)).start();

		Account xu=new Account("xu");
		(new Func(xu,100000)).start();
	}
}

注：必须要声明临界区，锁定account对象，不然会出错

正确结果：

错误结果：

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