Java 多线程

Posted 2020-11-30 esrevinud

Java线程编程

Thread类和Runnable接口

Runnable是Java中所有线程相关的类必须实现的接口

创建线程

有两种方式,继承Thread类和实现Runnable接口

继承Thread类

public class Main extends Thread{
    @Override
    public void run() {
        //调用getName()返回线程名称
        System.out.println(getName() + "   is running");
    }

    public static void main(String[] args) {
        //实例化Main对象
        Main one = new Main();
        Main two = new Main();
        Main three = new Main();

        //启动线程
        one.start();
        two.start();
        three.start();
    }
}

实现Runnable接口

public class Main implements Runnable{
    @Override
    public void run () {
        //Thread的类方法Thread.currentThread()返回当前线程对象,再调用getName()返回线程名称
        System.out.println(Thread.currentThread().getName() + "   is running");
    }

    public static void main(String[] args) {
        //实例化Main类
        Main one = new Main();
        Main two = new Main();
        Main three = new Main();

        //将Main的实例代入Thread构造函数,构造出Thread对象
        Thread the_one = new Thread(one);
        Thread the_two = new Thread(two);
        Thread the_three = new Thread(three);

        //启动线程
        the_one.start();
        the_two.start();
        the_three.start();
    }
}

线程间的资源共享

//个线程间共享用于控制循环的变量i
public class Main implements Runnable{
    // 这里的变量就是属于共享资源
    int i=0;
    // run方法内部是每个线程内部的资源和代码
    @Override
    public void run() {
         // Thread的类方法Thread.currentThread()返回当前线程对象,再调用getName()返回线程名称
        // System.out.println(Thread.currentThread().getName()+"   is running");
        for (; i < 10; i ++) {
            System.out.println(Thread.currentThread().getName() + "   is running for the "+i);
        }
        // System.out.println(message);
    }

    public static void main (String[] args) {
        //实例化Main类
        Main one = new Main();
        // Main two=new Main();
        // Main three=new Main();

        //将Main的实例代入Thread构造函数,构造出Thread对象
        Thread the_one = new Thread(one);
        Thread the_two = new Thread(one);
        Thread the_three = new Thread(one);

        //启动线程
        System.out.println(the_one.getId());
        System.out.println(the_two.getId());
        System.out.println(the_three.getId());
        the_one.start();
        the_two.start();
        the_three.start();
    }
}

设置线程优先级

//setPriority()设置，参数可以是常量也可以是[1,10]整数
the_one.setPriority(Thread.MAX_PRIORITY);
System.out.println(the_one.getPriority());      //输出打印10

优先级常量有三个等级

• Thread.MAX_PRIORITY
• Thread.MIN_PRIORITY
• Thread.NORM_PRIORITY

线程同步锁

使用synchronized修饰符,可修饰方法和语句块

修饰方法

//object method
public synchronized void printEach() {
    //once for loop
}

//static method
public static synchronized void printEach() {
    //once for loop
}

//statement block
//this表示为当前对象，也可以使用别的对象作为参数
synchronized(this) {
    //code
}