Java高级--多线程（2）多线程实例和线程安全问题解决方案

多线程实例

三个窗口同时卖一百张票 但是未解决线程安全问题

继承Thread类

package thread;

public class WindowsTest {
    public static void main(String[] args) {
        Window t1 = new Window();
        Window t2 = new Window();
        Window t3 = new Window();

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Window extends Thread {
    private static int ticket = 100; // 未解决线程安全问题，三个窗口都可以卖票号为100的票

    @Override
    public void run() {
        while (true) {
            if (ticket > 0) {
                System.out.println(getName() + "买票,票号为:" + ticket);
                ticket--;
            } else {
                break;
            }
        }
    }
}

实现Runnable接口

package thread;

public class WindowsTest01 {
    public static void main(String[] args) {
        Window1 w = new Window1();


        Thread t1 = new Thread(w);
        Thread t2 = new Thread(w);
        Thread t3 = new Thread(w);

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Window1 implements Runnable{

    private int ticket = 100;

    @Override
    public void run() {
        while (true){
            if(ticket>0){
                System.out.println(Thread.currentThread().getName() + "卖票，票号为"+ticket);
                ticket--;
            }
        }
    }
}

线程安全问题解决措施

在Java中，我们通过同步机制，来解决线程的安全问题。

方法一：同步代码块

synchronized(同步关键字){
	//需要被同步的代码
}

说明 ： 1. 操作共享对象数据的代码，即为需要被同步的代码 （不能包含少了，也不能包含多了）

​ 2. 同步监视器，俗称 锁 ， 任何一个类的对象，都可以充当锁 （要求：多个线程必须要共用同一把锁 ）

同步代码块处理实现Runnable接口的线程安全问题

在Runnable接口创建多线程的方式中，我们可以考虑使用this来充当同步监视器

package com.chen.java;

public class WindowsTest01 {
    public static void main(String[] args) {
        Window1 w = new Window1();


        Thread t1 = new Thread(w);
        Thread t2 = new Thread(w);
        Thread t3 = new Thread(w);

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Window1 implements Runnable{

    private int ticket = 100;

    @Override
    public void run() {
        while (true) {
            synchronized (this) {
                if (ticket > 0) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "卖票，票号为" + ticket);
                    ticket--;
                } else {
                    break;
                }
            }
        }
    }
}

同步代码块处理继承Thread类的线程安全问题

package com.chen.java;

public class WindowTest02 {
    public static void main(String[] args) {
        Window t1 = new Window();
        Window t2 = new Window();
        Window t3 = new Window();

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Window extends Thread {
    private static int ticket = 100;

    @Override
    public void run() {
        while (true) {
            synchronized (WindowTest02.class){ //Class class = Window2.class,Window2.class只会加载一次
            if (ticket > 0) {
                System.out.println(getName() + "买票,票号为:" + ticket);
                ticket--;
            } else {
                break;
            }
        }}
    }
}

方法二：同步方法

同步方法处理实现Runnable接口的线程安全问题

package com.chen.java;


public class WindowTest04 {
    public static void main(String[] args) {
        Window4 w = new Window4();


        Thread t1 = new Thread(w);
        Thread t2 = new Thread(w);
        Thread t3 = new Thread(w);

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Window4 implements Runnable{

    private int ticket = 100;

    @Override
    public void run() {
        while (true){
            show();
        }
    }

    private synchronized void show(){
        if(ticket>0){
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "卖票，票号为"+ticket);
            ticket--;
        }

    }

}

同步方法处理继承Thread类的方式中的线程安全问题

package com.chen.java;

public class WindowTest03 {
    public static void main(String[] args) {
        Windows t1 = new Windows();
        Windows t2 = new Windows();
        Windows t3 = new Windows();

        t1.setName("窗口一");
        t2.setName("窗口二");
        t3.setName("窗口三");

        t1.start();
        t2.start();
        t3.start();
    }
}

class Windows extends Thread {
    private static int ticket = 100; // 未解决线程安全问题，三个窗口都可以卖票号为100的票

    @Override
    public void run() {
        while (true) {
            show();
        }
    }

    private static synchronized void show(){
        if (ticket > 0) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "买票,票号为:" + ticket);
            ticket--;
        }
    }
}