Java多线程同步的一层对象/二层对象/三层对象写法对比

来源：互联网发布：java 生成6位随机数编辑：程序博客网时间：2024/04/29 21:29

前言:

在面向对象的思想下,线程的写法根据要创建的对象层级可以分为三种写法:
1,一层对象写法:采用extends Thread,复写父类的run()方法,直接建立一个线程实例对象的方式,这种方式简单,适用于单任务的单线程需求.在此不做过多讨论;
2,二层对象写法:采用implements Runnable接口,复写接口的run()方法,得到二级对象--通常称为任务对象;再通过将二级对象传入(负责main()方法的)一级对象的new Thread()构造参数,一级对象采用多态的Thread引用到run()方法;

import java.util.Random;//两个线程一起买票的例子:class FinalDemo1 implements Runnable {private int[] arr = new int[6];private int n=0;//private int num = 50;public void run() {for (int i = 0; i < 100; i++) {synchronized(this){if (/*num > 0 &&*/ n<6) {try {Thread.sleep(10);} catch (InterruptedException e) {e.printStackTrace();}//System.out.println(Thread.currentThread().getName() + "卖出了第"//+ num-- + "张票！");arr[n]= new Random().nextInt(10);n++;for(int a:arr){System.out.print(a);}                    System.out.println();}}}}}public class MyThreadDemo2 {public static void main(String[] args) {FinalDemo1 f = new FinalDemo1();new Thread(f, "A").start();new Thread(f, "B").start();new Thread(f, "C").start();}}

二层写法要注意:共享的资源一般写在私有属性上,因此建立线程时,不能new多个Runnable! 否则就是多线程执行多个相同的任务了;应该先new一个Runnable对象r,始终将这个对象传给多个new Thread(r)就行了.

3,三层对象写法:在二层写法的基础上,因为任务的复杂度,建立第三个对象--通常称为resource资源对象来负责建立不同的处理方法,常见的是一个生产式方法,一个消费式方法,或者要交替执行的两个其它方法;

因为资源是唯一的,有要共享的属性,所以更严谨的可以写成单例;如此,new Thread(new Runnable(res))形成三层对象完成一个线程的定义,并且多个任务的多个线程,都共同操作着一个res,为保证安全,只需对res中的方法进行同步就欧了;

举两个例子:

一个任务,多个线程的例子: 虽然可以用二层对象写法,但是抽出第三层资源对象后,可以对线程任务更好控制,如交替执行;

//两个线程填充一个数组问题:import java.util.Random;public class Test {        /*         * 声明一个共享数组，起两个线程，两个线程分别隔一段时间(可以写一个随机数)，         * 给数组中添加数据，每一个线程为数组添加3个数据即可。         *          */        public static void main(String[] args) {                                final ShareArr sharearr = ShareArr.getInstance();                                new Thread(new Runnable()                {                        public void run()                        {                                for(int i = 0;i<3;i++)                                {                                        sharearr.addNumFirst();                                }                        }                }).start();                                //因为使用了三级设计,对资源的调用同一个对象,因此不同的方法仍然共享private的属性,因此两个线程的第"i+1"个元素可以同步;                new Thread(new Runnable()                {                        public void run()                        {                                for(int i = 0;i<3;i++)                                {                                        sharearr.addNumSecond();                                }                        }                }).start();        }}class ShareArr {        private ShareArr(){};        private static ShareArr arr = null;        public static ShareArr getInstance()        {                if(arr == null)                {                        synchronized (ShareArr.class)                        {                                if(arr == null)                                {                                        arr = new ShareArr();                                }                        }                }                return arr;        }                private int[] array = new int[6];        private int i = 0;        boolean flag = true;        public synchronized void addNumFirst()        {                while(!flag)                {                        try {                                this.wait();                        } catch (InterruptedException e) {                                e.printStackTrace();                        }                }                try {                        Thread.sleep(1000);                } catch (InterruptedException e) {                        e.printStackTrace();                }                int num = new Random().nextInt();                System.out.println(Thread.currentThread().getName()+"给数组第"+(i+1)+"个元素赋值"+num);                array[i++] = num;                flag = false;                this.notify();        }                public synchronized void addNumSecond()        {                while(flag)                {                        try {                                this.wait();                        } catch (InterruptedException e) {                                e.printStackTrace();                        }                }                try {                        Thread.sleep(1000);                } catch (InterruptedException e) {                        e.printStackTrace();                }                int num = new Random().nextInt();                System.out.println(Thread.currentThread().getName()+"给数组第"+(i+1)+"个元素赋值"+num);                array[i++] = num;                flag = true;                this.notify();        }}

多任务,多线程的例子: 一般都得采用三层对象写法;

生产&消费的synchronized和lock方式例子:ProducerConsumerDemoclass  ProducerConsumerDemo2{public static void main(String[] args) {Resource r=new Resource();Producer pro=new Producer(r);Consumer con=new Consumer(r);Thread t1=new Thread (pro);Thread t2=new Thread (pro);Thread t3=new Thread (con);Thread t4=new Thread (con);t1.start();t2.start();t3.start();t4.start();System.out.println("Hello World!");}}class Resource {private String name;private int count=1;private boolean flag=false;public synchronized void set(String name){while(flag)try{wait();}catch(Exception e){}this.name=name+"--"+count++;System.out.println(Thread.currentThread().getName()+"...生产者..."+this.name);flag=true;this.notifyAll();}public synchronized void out(){while(!flag)try{wait();}catch(Exception e){}System.out.println(Thread.currentThread().getName()+"......消费者..."+this.name);flag=false;this.notifyAll();}}class Producer implements Runnable{private Resource res;Producer(Resource res){this.res=res;}public void run(){while (true){res.set("+商品+");}}}class Consumer implements Runnable{private Resource res;Consumer(Resource res){this.res=res;}public void run(){while(true){res.out();}}}import java.util.concurrent.locks.*;class  ProducerConsumerDemo2{public static void main(String[] args) {Resource r=new Resource();Producer pro=new Producer(r);Consumer con=new Consumer(r);Thread t1=new Thread (pro);Thread t2=new Thread (pro);Thread t3=new Thread (con);Thread t4=new Thread (con);t1.start();t2.start();t3.start();t4.start();System.out.println("Hello World!");}}class Resource {private String name;private int count=1;private boolean flag=false;private Lock lock=new ReentrantLock();//接口类private Condition condition_pro=lock.newCondition();private Condition condition_con=lock.newCondition();public void set(String name)throws InterruptedException//中断异常{lock.lock();try{while(flag)condition_pro.await();//condition的抛异wait常方法,把pro的线程停止.this.name=name+"--"+count++;System.out.println(Thread.currentThread().getName()+"...生产者..."+this.name);flag=true;condition_con.signal();}finally{lock.unlock();}}public  void out()throws InterruptedException{lock.lock();try{while(!flag)condition_con.await();//try{wait();}catch(Exception e){}System.out.println(Thread.currentThread().getName()+"...消费者......"+this.name);flag=false;condition_pro.signal();//this.notifyAll();唤醒all}finally{lock.unlock();}}}class Producer implements Runnable{private Resource res;Producer(Resource res){this.res=res;}public void run(){while (true){try{res.set("+商品+");}catch (InterruptedException e){}}}}class Consumer implements Runnable{private Resource res;Consumer(Resource res){this.res=res;}public void run(){while(true){try{res.out();}catch (InterruptedException e){}}}}

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