The process of simple animation is a series of events where a figure appears (is drawn), disappears (is erased in some manner), and reappears (is redrawn) in another location. As this process continues, the figure appears to be moving. Since a computer can draw and erase a figure faster than we can see it happen, we must be able to control the time that a figure remains viewable on the screen to accomplish a simple animation.

a timing method to be added to your program
public static void pause (int time)
{
     try                            //opens an exception handling statement
     {
          Thread.sleep(time);
     }
     catch(InterruptedException e)  //captures the exception
     {
     }
}

 Note: Thread.sleep(5000) will sleep for approximate 5 seconds (a long time).

(snippets of code to show insertions) . . .
public class Demo extends JPanel implements ActionListener
{
     Timer time = new Timer(5, this); // 'this' refers to the ActionListener
. . .
    public void paintComponent(g)
    {
         time.start(); //engage the timer
         . . .

If time is a variable of type Timer, then the statement
time = new Timer(millisDelay,listener);
creates a timer with a delay of millisDelay milliseconds between events (where 1000 milliseconds equals one second).

The process of moving a figure on the screen necessitates knowing the coordinate locations of the various positions of the figure on the screen. It is too cumbersome to code every single location. Instead, the figure is expressed using one or more variables that are accessed by the computer to position and reposition the figure on the screen.

If the figure that you are moving is one of the simple primitive shapes that are already method-defined, such as simple rectangles and circles, the animation "formula" process is quite simple.

Animation Formulas for existing method-defined figures (draw or fill):
Consider this rectangle: g.drawRect(35, 45, 25, 35);
• To move the rectangle horizontally, we use g.drawRect(x, 45, 25, 35);
Replace the x-coordinate with a variable to move horizontally.
• To move the rectangle vertically, we use g.drawRect(35, y, 25, 35);
Replace the y-coordinate with a variable to move vertically.
• To move the rectangle diagonally, we use g.drawRect(x, y, 25, 35);
Replace the x and y coordinates with variables to move diagonally.
Then instruct the computer to change the values of x (and/or y) in a manner that meets the speed and direction of the desired movement.

Rectangle moved horizontally across screen.

The process of erasing a figure is accomplished with repaint( ); which calls the paintComponent method. It tells the system that a component needs to be redrawn. Think of it as refreshing the viewing area.

Animations require the use of an ActionListener. Remember that an ActionListener is an "event handler" which requires the import statement import java.awt.event.*;
The event handler class specifies that the class will implement an ActionListener interface:
public class ClassName extends JPanel implements ActionListener {
The following method is needed to implement the action listener interface every 5 milliseconds (in this example):
public void actionPerformed(ActionEvent e) {


//Program to Move Rectangle Across the JPanel

Animation Formulas are a bit harder for method-defined polygons:
Consider the arrow figure shown below. Yes, this can be a method-defined 7-sided polygon since all of its sides are line segments. The first box shows the coordinates of where we want the arrow to be located when it starts. We will animate the arrow moving horizontally to the right.