java同步線程(二)

           同步方法

同步方法：

使用synchronized關(guān)鍵字來(lái)修飾某個(gè)方法溉躲，則該方法稱為同步方法寸认。
同步方法的同步監(jiān)視器是this，也就是該對(duì)象本身偏塞。

通過(guò)同步方法可以非常方便地實(shí)現(xiàn)線程安全的類，線程安全的類具有如下特征神汹。

1古今、該類的對(duì)象可以被多個(gè)線程安全地訪問(wèn)。

2捉腥、每個(gè)線程調(diào)用該對(duì)象的任意方法之后都將得到正確結(jié)果。

3桃漾、每個(gè)線程調(diào)用該對(duì)象的任意方法之后拟逮，該對(duì)象狀態(tài)依然保持合理的狀態(tài)。

實(shí)現(xiàn)方式如下：

package com.zmy.bank;

public class Account {
    //封裝賬戶編號(hào)敦迄，賬戶余額兩個(gè)Eield
    private String accountNo;
    private double balance;
    public Account(String accountNo,double balance)
    {
        this.accountNo=accountNo;
        this.balance=balance;
    }
    //創(chuàng)建的getter和setter方法

    public String getAccountNo() {
        return accountNo;
    }

    public void setAccountNo(String accountNo) {
        this.accountNo = accountNo;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }


    public synchronized void draw(double drawAmount)
    {
        if(balance>=drawAmount)
        {
            System.out.println(Thread.currentThread().getName()+"取錢成功!吐出鈔票"+drawAmount);
            try{
                Thread.sleep(1);

            }catch (InterruptedException e)
            {
                e.printStackTrace();
            }
            balance-=drawAmount;
            System.out.println("\t余額為:"+balance);
        }
        else {
            System.out.println(Thread.currentThread().getName()+"取錢失敗苦囱！余額不足!");
        }
    }
    @Override
    public int hashCode() {
        return accountNo.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (this==obj)
            return true;
        if (obj !=null&&obj.getClass()==Account.class)
        {
            Account target=(Account)obj;
            return target.getAccountNo().equals(accountNo);
        }
        return false;
    }


}

package com.zmy.bank;

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;
    }
    //當(dāng)多個(gè)線程修改同一個(gè)共享數(shù)據(jù)時(shí)，將涉及數(shù)據(jù)安全性問(wèn)題

    @Override
    public void run() {
        if (account.getBalance() >= drawAmount) {
            //突出鈔票
            account.draw(drawAmount);
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        } else {
            System.out.println(getName() + "取錢失斝嗯椤喉刘！余額不足！");
        }
    }
}

package com.zmy.bank;

public class DrawTest {
    public static void main(String[] args) {
        //創(chuàng)建一個(gè)賬戶
        Account acct=new Account("123456",1000);
        //simulation two thread draw money from one account
        new DrawThread("甲",acct,800).start();
        new DrawThread("乙",acct,800).start();
    }
}

synchronized 不能修飾構(gòu)造器睦裳、屬性