对await(),notify()的理解

await(),notify()是java Object类的方法.在两个线程同时访问一个对象的时候可以利用这2个方法实现线程的通信.看下面的例子.

public class Account {
    private String accountNo;
    private double balance;
    private boolean flag = false;
    public Account() {
    }
    public Account(String accountNo, double balance) {
        this.accountNo = accountNo;
        this.balance = balance;
    }
    public void setAccountNo(String accountNo) {
        this.accountNo = accountNo;
    }
    public String getAccountNo() {
        return this.accountNo;
    }
    public double getBalance() {
        return this.balance;
    }
    public synchronized void draw(double drawAmount) {
        try {
            //如果flag为假，表明账户中还没有人存钱进去，则取钱方法阻塞
            if (!flag) {
                wait();
            } else {
                System.out.println(Thread.currentThread().getName() +
                        " 取钱:" + drawAmount);
                balance -= drawAmount;
                System.out.println("账户余额为：" + balance);
                //将标识账户是否已有存款的旗标设为false。
                flag = false;
                notify();
            }
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
    public synchronized void deposit(double depositAmount) {
        try {
            //如果flag为真，表明账户中已有人存钱进去，则存钱方法阻塞
            if (flag) {
                wait();
            } else {
                //执行存款
                System.out.println(Thread.currentThread().getName() +
                        " 存款:" + depositAmount);
                balance += depositAmount;
                System.out.println("账户余额为：" + balance);
                //将表示账户是否已有存款的旗标设为true
                flag = true;
                //唤醒其他线程
                notify();
            }
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
}
public class DepositThread extends Thread {
    private Account account;
    private double depositAmount;

    public DepositThread(String name, Account account,
                         double depositAmount) {
        super(name);
        this.account = account;
        this.depositAmount = depositAmount;
    }

    public void run() {
        for (int i = 0; i < 100; i++) {
            account.deposit(depositAmount);
        }
    }
}
public class DrawThread extends Thread {
    private Account account;
    private double drawAmount;

    public DrawThread(String name, Account account,
                      double drawAmount) {
        super(name);
        this.account = account;
        this.drawAmount = drawAmount;
    }

    public void run() {
        for (int i = 0; i < 100; i++) {
            account.draw(drawAmount);
        }
    }
}
public class TestDraw {
    public static void main(String[] args) {
        Account acct = new Account("1234567", 0);
        new DrawThread("取钱者", acct, 800).start();
        new DepositThread("存款者甲", acct, 800).start();
    }
}

DepositThread线程负责存钱,DrawThread线程负责取钱.flag为true时表示有钱,DepositThread线程调用await实现等待.flag为false时表示没有钱,DrawThread线程调用await实现等待.当flag为true时DrawThread实现取钱,之后调用notify(),通知DepositThread可以来存钱.当flag为false时DepositThread实现存钱,之后调用notify(),通知DrawThread可以来存钱.