visualsuspendresume.java

Java Thread Programming (Source

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class VisualSuspendResume 
			extends JPanel 
			implements Runnable {

	private static final String[] symbolList = 
			{ "|", "/", "-", "\\", "|", "/", "-", "\\" };

	private Thread runThread;
	private JTextField symbolTF;

	public VisualSuspendResume() {
		symbolTF = new JTextField(); 
		symbolTF.setEditable(false);
		symbolTF.setFont(new Font("Monospaced", Font.BOLD, 26));
		symbolTF.setHorizontalAlignment(JTextField.CENTER);

		final JButton suspendB = new JButton("Suspend");
		final JButton resumeB = new JButton("Resume");

		suspendB.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					suspendNow();
				}
			});

		resumeB.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					resumeNow();
				}
			});
		
		JPanel innerStackP = new JPanel();
		innerStackP.setLayout(new GridLayout(0, 1, 3, 3));
		innerStackP.add(symbolTF);
		innerStackP.add(suspendB);
		innerStackP.add(resumeB);

		this.setLayout(new FlowLayout(FlowLayout.CENTER));
		this.add(innerStackP);
	}

	private void suspendNow() {
		if ( runThread != null ) { // avoid NullPointerException
			runThread.suspend();
		}
	}

	private void resumeNow() {
		if ( runThread != null ) { // avoid NullPointerException
			runThread.resume();
		}
	}

	public void run() {
		try {
			// Store this for the suspendNow() and 
			// resumeNow() methods to use.
			runThread = Thread.currentThread();
			int count = 0;

			while ( true ) {
				// each time through, show the next symbol
				symbolTF.setText(
					symbolList[ count % symbolList.length ]);
				Thread.sleep(200);
				count++;
			}
		} catch ( InterruptedException x ) {
			// ignore
		} finally {
			// The thread is about to die, make sure that the 
			// reference to it is also lost.
			runThread = null;
		}
	}

	public static void main(String[] args) {
		VisualSuspendResume vsr = new VisualSuspendResume();
		Thread t = new Thread(vsr);
		t.start();

		JFrame f = new JFrame("Visual Suspend Resume");
		f.setContentPane(vsr);
		f.setSize(320, 200);
		f.setVisible(true);
		f.addWindowListener(new WindowAdapter() {
				public void windowClosing(WindowEvent e) {
					System.exit(0);
				}
			});
	}
}