Java多线程银行存钱
小虚竹and掘金 人气:0一、题目描述
题目：模拟一个简单的银行系统，使用两个不同的线程向同一个账户存钱。
实现：使用特殊域变量volatile实现同步。
二、解题思路
创建一个类：SynchronizedBankFrame，继承JFrame类
写一个内部类Bank
- 定义一个account变量，来表示账户。
- deposit():一个存钱的方法
- getAccount()：显示账户余额的方法。
写一个内部类Transfer，实现Runnable接口
在run方法中实现向账户存钱的功能。
volatile关键字为变量访问提供了一种免锁机制。使用volatile关键字修饰变量，每次使用该变量就要重新计算，而不是使用寄存器中的值。
volatile不会提供原子操作，也不能用来修饰final类型的变量。
三、代码详解
SynchronizedBankFrame
package com.xiaoxuzhu;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JButton;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.GridLayout;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import java.awt.Font;
import javax.swing.UIManager;
/**
* Description:
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修改记录:
* 修改后版本 修改人 修改日期 修改内容
* 2022/5/14.1 xiaoxuzhu 2022/5/14 Create
* </pre>
* @date 2022/5/14
*/
public class SynchronizedBankFrame extends JFrame {
/**
*
*/
private static final long serialVersionUID = 2671056183299397274L;
private JPanel contentPane;
private JTextArea thread1TextArea;
private JTextArea thread2TextArea;
/**
* Launch the application.
*/
public static void main(String[] args) {
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
} catch (Throwable e) {
e.printStackTrace();
}
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
SynchronizedBankFrame frame = new SynchronizedBankFrame();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public SynchronizedBankFrame() {
setTitle("使用volatile实现线程同步");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(new BorderLayout(0, 0));
JPanel buttonPanel = new JPanel();
contentPane.add(buttonPanel, BorderLayout.SOUTH);
JButton startButton = new JButton("开始存钱");
startButton.setFont(new Font("微软雅黑", Font.PLAIN, 16));
startButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
do_button_actionPerformed(arg0);
}
});
buttonPanel.add(startButton);
JPanel processPanel = new JPanel();
contentPane.add(processPanel, BorderLayout.CENTER);
processPanel.setLayout(new GridLayout(1, 2, 5, 5));
JPanel thread1Panel = new JPanel();
processPanel.add(thread1Panel);
thread1Panel.setLayout(new BorderLayout(0, 0));
JLabel thread1Label = new JLabel("一号线程");
thread1Label.setFont(new Font("微软雅黑", Font.PLAIN, 16));
thread1Label.setHorizontalAlignment(SwingConstants.CENTER);
thread1Panel.add(thread1Label, BorderLayout.NORTH);
JScrollPane thread1ScrollPane = new JScrollPane();
thread1Panel.add(thread1ScrollPane, BorderLayout.CENTER);
thread1TextArea = new JTextArea();
thread1TextArea.setFont(new Font("微软雅黑", Font.PLAIN, 16));
thread1ScrollPane.setViewportView(thread1TextArea);
JPanel thread2Panel = new JPanel();
processPanel.add(thread2Panel);
thread2Panel.setLayout(new BorderLayout(0, 0));
JLabel thread2Label = new JLabel("二号线程");
thread2Label.setFont(new Font("微软雅黑", Font.PLAIN, 16));
thread2Label.setHorizontalAlignment(SwingConstants.CENTER);
thread2Panel.add(thread2Label, BorderLayout.NORTH);
JScrollPane thread2ScrollPane = new JScrollPane();
thread2Panel.add(thread2ScrollPane, BorderLayout.CENTER);
thread2TextArea = new JTextArea();
thread2TextArea.setFont(new Font("微软雅黑", Font.PLAIN, 16));
thread2ScrollPane.setViewportView(thread2TextArea);
}
protected void do_button_actionPerformed(ActionEvent arg0) {
Bank bank = new Bank();
Thread thread1 = new Thread(new Transfer(bank, thread1TextArea));
thread1.start();
Thread thread2 = new Thread(new Transfer(bank, thread2TextArea));
thread2.start();
}
private class Transfer implements Runnable {
private Bank bank;
private JTextArea textArea;
public Transfer(Bank bank, JTextArea textArea) {
this.bank = bank;
this.textArea = textArea;
}
public void run() {
for (int i = 0; i < 10; i++) {
bank.deposit(10);
String text = textArea.getText();
textArea.setText(text + "账户的余额是：" + bank.getAccount() + "\n");
}
}
}
private class Bank {
private volatile int account = 100;// 将域变量用volatile修饰
public void deposit(int money) {// 向账户中存钱
account += money;
}
public int getAccount() {// 获得账户余额
return account;
}
}
}
多学一个知识点
每个线程是存在缓存内存的。且缓存内存是对其他线程不可见的。这就是内存不可见问题。
来验证下
package com.xiaoxuzhu;
/**
* Description: 证明线程是存在缓存内存的
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修改记录:
* 修改后版本 修改人 修改日期 修改内容
* 2022/5/14.1 xiaoxuzhu 2022/5/14 Create
* </pre>
* @date 2022/5/14
*/
public class VolatileDemo {
public static void main(String[] args) {
ThreadDemo threadDemo = new ThreadDemo();
//启动线程 改值
new Thread(threadDemo).start();
while (true){
if(threadDemo.isFlag()){
System.out.println("主线程读到的flag是true");
break;
}
}
}
static class ThreadDemo implements Runnable{
private boolean flag = false;
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
@Override
public void run() {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
flag = true;
System.out.println("flag 线程执行改为："+isFlag());
}
}
}
主线程得到的是false，新线程已经把值修改为true了。证实每个线程是存在缓存内存的
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