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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: ProducerConsumerDemo 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; 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) { } } } }
黑马程序员--多线程同步的一层对象/二层对象/三层对象写法对比
原文地址：http://blog.csdn.net/marching21/article/details/39404133
