Using Timers in graphics programs

Important

There are three different timer classes in Java and the all work differently!
import java.util.Timer is used for timers in programs that do NOT use graphics.
import javax.swing.Timer is used for timers in programs that do use Swing graphics. Since HSA2 graphics is based on Swing, this is what you must use.

Making Timers

You create a Swing Timer object like this: Timer timer = new Timer(TIMERSPEED, this);

• The name of the timer object here is "timer". It is a global variable because it is created outside of any method.
• If you had to make a second timer, you could call it "timer2" or a name that describes what it is for: "enemySpawnTimer" ... Oh! but it will want to use the same "actionPerformed()" method so it will be tricky. If you need a second timer, I'll have to show you how to do it.
  Or look at this example
• TIMERSPEED is how often the timer runs in milliseconds.
• "this" means that the "actionPerformed()" that the timer runs is in this class

You also have to add the text implements ActionListener to the end of your class definition. See the sample program below.

Start the timer using timer.start();. If you don't do this, it will never run.

Getting the timer to do something

The timer object creates an event that triggers a method called "actionPerformed" to be run. This is run repeately, every x millisiconds (or TIMERSPEED milliseconds)

So you have to type in the actionPerformed part exactly how it is below. Also note that it cannot be inside an existing method.

@Override
public void actionPerformed(ActionEvent ev) {
	//put code here to do something
}

Sample code to illustrate Timers and using booleans

Notice how I am using a boolean variable to tell if the program is paused or not.

It has to be a global variable so that it is accessible from more than one place (oops! actually, it is only being used in the constructor which has the main loop) and so that it maintains its state.

import java.awt.Color;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;

import hsa2.GraphicsConsole;

/***********************************************************
 This program illustrates how to use a timer.
 It also shows the benefits of using a boolean variable 
 and the correct method of using booleans. 
 Mouse clicking was introduced earlier.
 ************************************************************/

/* You have to add "implements ActionListener" here. */
public class TimerExample implements ActionListener {
	public static void main(String[] args) {
		new TimerExample();

	}
	
	GraphicsConsole gc = new GraphicsConsole();	
	Rectangle r1 = new Rectangle(100,100,100,50);
	
	final static int TIMERSPEED = 200; //ms
	final static int MAXTIME = 15; //seconds
	
	Timer timer = new Timer(TIMERSPEED, this);
	
	boolean isPaused = false;
	double seconds = 0.0;
	
	TimerExample() {
		gc.setBackgroundColor(Color.BLACK);
		gc.clear();
		gc.setLocationRelativeTo(null);
		gc.setTitle("Click the mouse to pause");
		gc.setColor(Color.CYAN);
		gc.enableMouse();
		timer.start();
		
		while(seconds < MAXTIME) {
			
			if (gc.getMouseClick() > 0) {
				isPaused = !isPaused;
			}
			
			if (isPaused) {
				gc.setTitle("Game paused");
				if (timer.isRunning()) timer.stop();	//only stop it once, not repeatedly.
			} else {
				gc.setTitle("Click the mouse to pause");
				if (! timer.isRunning() ) timer.start();	//only start it once, not repeatedly
			}
			
			synchronized(gc) {
			
				gc.clear();
				if (!isPaused) gc.fillRect(r1.x, r1.y, r1.width, r1.height);
				
				gc.drawString("TIME=" + seconds, 50,50);				
			}
			
			gc.sleep(10);
		} //end of while loop
		
		gc.close();
		
	} //end of program.
	
	
	/* Timer creates an action event every TIMERSPEED milliseconds that runs this method */
	@Override
	public void actionPerformed(ActionEvent ev) {
		seconds += TIMERSPEED/1000.0; //All that is being done here is to add a second (or half a second) to the variable seconds.
		
		/*other things could go here ... like move enemies, etc. 
		 * Or they could go in the main game loop.
		 * The advantage of doing them here is that they are completely independent of what happens in the main game loop
		 * and how fast the animation is drawn. i.e. the enemies would move at a constant speed, regardless of the framerate.
		 */
	}
}