java多线程编程核心技术学习-1

实现多线程的两种方式

继承Thread类，重写Thread类中的run方法

public class MyThread extends Thread{
    @Override
    public void run(){
        super.run();
        System.out.println("this is myThread run");
    }
}

public static void main(String[] args) {
    Thread myThread=new MyThread();
    myThread.start();
    System.out.println("mian function is over");
}

注意：代码的顺序并不是线程的执行顺序，start的顺序也不是多个线程的执行顺序。

实现Runable接口

java是单继承的，一个子类只能去继承一个父类，所以如果线程类已经继承了其他父类，那么就不能采用继承thread类来实现多线程了

public class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("this is myrunable running");
    }
}

public class Test {
    public static void main(String[] args) {
        Runnable myRunnable=new MyRunnable();
        Thread thread=new Thread(myRunnable);
        thread.start();
        System.out.println("main is runing");
    }
}

 实例变量与线程安全：

数据不共享的实例，两个线程中分别创建了两个thread实例，各种都是独立的count

public class MyThread extends Thread{
    private int count=5;
    public MyThread(String name) {
        super();
        this.setName(name);
    }
    @Override
    public void run(){
        super.run();
        while(count>0){
            count--;
            System.out.println(this.currentThread().getName());
            System.out.println(count);
        }
    }
}

public class Test {
    public static void main(String[] args) {
        Thread thread1=new MyThread("A");
        Thread thread2=new MyThread("B");
        thread1.start();
        thread2.start();
    }
}

数据共享的实例

public class MyThread extends Thread {
    private int count = 5;
    @Override
    public void run() {
        super.run();
        count--;
        System.out.println(this.currentThread().getName()+count);
    }
}

public class Test {
    public static void main(String[] args) {
        Thread thread=new MyThread();
 
        Thread thread1=new Thread(thread, "A");
        Thread thread2=new Thread(thread,"B");
        Thread thread3=new Thread(thread, "C");
        thread1.start();
        thread2.start();
        thread3.start();
    }
}

可以在方法上加同步锁，syschronized，这样每一个线程在执行这个方法前需要先尝试去获取这把锁，获取不到就会等待，一直到获取到。

public class MyThread extends Thread {
    private int count = 5;
    @Override
    synchronized public void run() {
        super.run();
        count--;
        System.out.println(this.currentThread().getName()+count);
    }
}

下面是一个多线程非安全对的共享变量实例：

在实例中共享了静态变量usanameRef和passwordRef

public class Alogin extends Thread{
    @Override
    public void run(){
        LoginServlet.doPost("a", "aa");
    }
}
public class Blogin extends Thread{
    @Override
    public void run(){
        LoginServlet.doPost("b", "bb");
    }
}
public class LoginServlet {
    private static String usenameRef;
    private static String passwordRef;
  synchronized public static void doPost(String usename,String password){
        try {
            usenameRef=usename;
 
            if(usename.equals("a")){
                Thread.sleep(2000);
            }
            passwordRef=password;
            System.out.println("username="+usenameRef+"password="+password);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
public class Test {
    public static void main(String[] args) {
        Alogin alogin=new Alogin();
        alogin.start();
        Blogin blogin=new Blogin();
        blogin.start();
    }
}

参考： 《java多线程编程核心技术》

https://blog.csdn.net/iaiti/article/details/53314149