[英]Changing the value of a variable in a Java Thread
所以我正在學習線程,但似乎無法獲得使用線程的程序。
基本代碼是:
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
import java.awt.GridLayout;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.Dimension;
public class CLASS1 extends JFrame implements KeyListener
{
public CLASS2 class2Variable1 = new CLASS2();
public CLASS2 class2Variable2 = new CLASS2();
public Thread thread1 = new Thread(class2Variable1);
public Thread thread2 = new Thread(class2Variable2);
public CLASS1()
{
//Not Important for example
}
public static void main(String[] args)
{
CLASS1 class1 = new CLASS1();
class1.createAndShowGUI();
}
public void createAndShowGUI()
{
CLASS1 frame = new CLASS1();
frame.setPreferredSize(new Dimension(400,200));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel contentPane = new JPanel(new GridLayout());
frame.setContentPane(contentPane);
frame.addKeyListener(frame);
frame.add(class2Variable1);
frame.add(class2Variable2);
thread1.start();
thread2.start();
frame.pack();
frame.setVisible(true);
}
public void keyPressed(KeyEvent e)
{
class2Variable1.speed = class2Variable1.speed + 10;
class2Variable1.changeText("CHANGED VALUE TO: " + class2Variable1.speed);
//Also Tried class2Variable1.labelText.setText("CHANGED VALUE");
class2Variable1.revalidate();
class2Variable1.repaint();
}
public void keyTyped(KeyEvent e)
{
}
public void keyReleased(KeyEvent e)
{
}
}
class CLASS2 extends JPanel implements Runnable
{
public int speed = 0;
public JLabel labelText = new JLabel(); //Also tried Initializing it here
public void changeText(String text)
{
labelText.setText(text);
labelText.repaint();
}
public void run()
{
addStuff();
}
public CLASS2()
{
setLayout(new GridLayout());
}
public void addStuff()
{
labelText.setText("INITIAL VALUE");
add(labelText);
}
}
所有的KeyEvent都起作用,但是如果我用messageDialog檢查變量var1,它會向我顯示初始化(0)處的值,而不是線程(100)的值。 即使使用setText,我也無法更改JLabel中的文本。
更改變量var1
不會更改標簽的文本。 您必須使用更改后的值調用varLabel.setText
。
另請閱讀有關swing線程的這篇文章: http : //docs.oracle.com/javase/7/docs/api/javax/swing/package-summary.html#threading
解決方案應如下所示:
public void run()
{
var1 = 100;
SwingUtilities.invokeLater(new Runnable() {
public void run() {
varLabel.setText(String.valueOf(var1));
// varLabel.repaint(); // might be necessary?
}
});
}
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