Java Reference
In-Depth Information
Example 15−2: Clock.java
package com.davidflanagan.examples.applet;
import java.applet.*; // Don't forget this import statement!
import java.awt.*; // Or this one for the graphics!
import java.util.Date; // To obtain the current time
import java.text.DateFormat; // For displaying the time
/**
* This applet displays the time, and updates it every second
**/
public class Clock extends Applet implements Runnable {
Label time; // A component to display the time in
DateFormat timeFormat; // This object converts the time to a string
Thread timer; // The thread that updates the time
volatile boolean running; // A flag used to stop the thread
/**
* The init method is called when the browser first starts the applet.
* It sets up the Label component and obtains a DateFormat object
**/
public void init() {
time = new Label();
time.setFont(new Font("helvetica", Font.BOLD, 12));
time.setAlignment(Label.CENTER);
setLayout(new BorderLayout());
add(time, BorderLayout.CENTER);
timeFormat = DateFormat.getTimeInstance(DateFormat.MEDIUM);
}
/**
* This browser calls this method to tell the applet to start running.
* Here, we create and start a thread that will update the time each
* second. Note that we take care never to have more than one thread
**/
public void start() {
running = true; // Set the flag
if (timer == null) { // If we don't already have a thread
timer = new Thread(this); // Then create one
timer.start();
// And start it running
}
}
/**
* This method implements Runnable. It is the body of the thread. Once
* a second, it updates the text of the Label to display the current time
**/
public void run() {
while(running) { // Loop until we're stopped
// Get current time, convert to a String, and display in the Label
time.setText(timeFormat.format(new Date()));
// Now wait 1000 milliseconds
try { Thread.sleep(1000); }
catch (InterruptedException e) {}
}
// If the thread exits, set it to null so we can create a new one
// if start() is called again.
timer = null;
}
