今天学习JAVA的多线程,看书看到一半,心血来潮,写了个程序,错误百出,不过也巩固了知识,程序如下:
//Sell.java
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class Sell extends JFrame implements ActionListener {
JTextArea taOut;
JButton btnStart;
JButton btnStop;
JTextField jtf;
Producethread produce;
Customthread customer;
Things thing;
JPanel p1;
JScrollPane p;
public Sell()
{
p1 = new JPanel();
taOut = new JTextArea(20,30);
p1.add(taOut);
p = new JScrollPane(p1);
p.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
p.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
btnStart = new JButton("Start");
btnStart.addActionListener(this);
btnStop = new JButton("Stop");
btnStop.addActionListener(this);
jtf = new JTextField(6);
getContentPane().add(p);
getContentPane().add(jtf);
getContentPane().add(btnStart);
getContentPane().add(btnStop);
getContentPane().setLayout(new FlowLayout());
thing = new Things(taOut);
setTitle("Sell Test");
setBounds(100,0,370,460);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}
public void actionPerformed(ActionEvent ae)
{
if (ae.getActionCommand().equals("Start"))
{
produce = new Producethread(thing);
customer = new Customthread(thing);
customer.setSpeed(jtf.getText());
produce.start();
customer.start();
}
if ( ae.getActionCommand().equals("Stop"))
{
produce.stop();
customer.stop();
}
}
public static void main(String[] args)
{
Sell se = new Sell();
}
}
class Producethread extends Thread {
Things th;
public Producethread(Things thing)
{
th = thing;
}
public void run()
{
while(true)
{
th.addProduce();
try{
sleep(500);
}
catch(InterruptedException ie){
System.err.println("ERR:" + ie.toString());
}
}
}
}
class Customthread extends Thread {
Things th;
int sh;
public Customthread(Things thing)
{
th = thing;
}
public void run()
{
while(true)
{
th.sellProduce();
try{
sleep((int)(Math.random()*sh));
}
catch(InterruptedException ie){
System.err.println("ERR:" + ie.toString());
}
}
}
public void setSpeed(String s)
{
sh=Integer.parseInt(s)*2;
}
}
class Things {
JTextArea out;
int total;
private final static int MAX = 50;
public Things(JTextArea taOut)
{
out=taOut;
total=10;
}
public synchronized void addProduce()
{
try{
if (total<MAX)
{
total++;
out.append("生产一产品加入仓库\n库存:"+ total + "\n");
}else{
out.append("满仓,暂停生产,等待中!\n");
wait();
}
}
catch(InterruptedException ie){
System.err.println("ERR:" + ie.toString());
}
notify();
}
public synchronized void sellProduce()
{
try{
if (total>0)
{
total--;
out.append("出售一产品\n库存:"+ total + "\n");
}else{
out.append("缺货,等待生产中!\n");
wait();
}
}
catch(InterruptedException ie){
System.err.println("ERR:" + ie.toString());
}
notify();
}
}
程序能够正确运行,按正常方式操作是没有问题的,但当连续按两次或一上Start的时候,问题就来了,在actionPerformed方法中,处理Start是重新实例化两个线程对象并运行,但如果这两个对象原来就在运行中,就会使旧的两个对象变成不受控制,不能停止了,修改方法可以在重新实例化前增加调用stop()方法。或增加一个变量,判断两个对象是否在运行,是就不执行重新实例化。
在测试中,发现了stop()方法调用后,是不能用start()方法重新另其启动的。(书上没有明确写出) 。连续调用同一个线程对象两次start()方法将会出错,stop()方法不会.