实例1
package 多线程; /* * 多窗口售票 * 此程序为错误程序,每张票买了四次 * */ class ticket extends Thread{ private int ticket=100; public void run() { while(true) { if(ticket>0) { System.out.println("sales:"+ticket--); } } } } public class tick { public static void main(String[] args) { ticket t0=new ticket(); ticket t1=new ticket(); ticket t2=new ticket(); ticket t3=new ticket(); t0.start(); t1.start(); t2.start(); t3.start(); } }
示例代码2
解决多线程共享变量问题:声明实现runnable接口的类
解决打印0,-1,-2票:使用同步代码块
package 多线程; /* * 多窗口售票 * implements Runnable * */ class ticket implements Runnable{ private int ticket=100; public void run() { while(true) { synchronized (this) { if(ticket>0) { try{Thread.sleep(10);}catch(Exception e){} System.out.println(Thread.currentThread().getName()+"sales:"+ticket--); } } } } } public class tick { public static void main(String[] args) { ticket t=new ticket(); Thread Th0=new Thread(t); Thread Th1=new Thread(t); Thread Th2=new Thread(t); Thread Th3=new Thread(t); Th0.start(); Th1.start(); Th2.start(); Th3.start(); } }
同步代码函数
package song.yan; class Bank{ private int sum; //同步代码块 /*public void add(int n) { synchronized(this) { sum=sum+100; try{Thread.sleep(100);}catch(Exception e){} System.out.println("sum="+sum); } }*/ //同步函数 public synchronized void add(int n) { sum=sum+100; try{Thread.sleep(100);}catch(Exception e){} System.out.println("sum="+sum); } } class Demos implements Runnable{ private Bank b= new Bank(); public void run() { for(int i=0;i<3;i++) { b.add(100); } } } public class tick{ public static void main(String[] args) { Demos d=new Demos(); Thread t1=new Thread(d); Thread t2= new Thread(d); t1.start(); t2.start(); } }
//
package song.yan.com; /* * 将同步设在run() * 将变成单线程问题 * * */ class Ticks implements Runnable{ private int num=1000; public synchronized void run() { while(true) { if(num>0) { System.out.println(Thread.currentThread().getName()+"num="+num--); } } } } public class tick{ public static void main(String[] args) { Ticks d=new Ticks(); Thread t1=new Thread(d); Thread t2= new Thread(d); Thread t3=new Thread(d); Thread t4= new Thread(d); t1.start(); t2.start(); t3.start(); t4.start(); } }
正确使用同步函数:将需要同步的部分单独写在synconized函数中,在run函数中调用
package song.yan.com; /* * 将同步设在run() * 将变成单线程问题 * * */ class Ticks implements Runnable{ private int num=2000; public void run() { while(true) { show(); } } public synchronized void show() { if(num>0) { System.out.println(Thread.currentThread().getName()+"num="+num--); } } } public class tick{ public static void main(String[] args) { Ticks d=new Ticks(); Thread t1=new Thread(d); Thread t2= new Thread(d); Thread t3=new Thread(d); Thread t4= new Thread(d); t1.start(); t2.start(); t3.start(); t4.start(); } }