Swing Hacks

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Chapter 12, Miscellany

#90 Create Demonstrations with the Robot Class

HACK

H A C K

#90

Create Demonstrations with the Robot Class

Hack #90

Use the Robot class to control the mouse cursor and create interactive

software features.

One of the coolest things about Swing is that you can often use a class for

something completely different than what it was originally intended. The

java.awt.Robot class, for example, can move the mouse cursor programmat-

ically. This feature was originally intended for use by automated testing

tools (hence the name Robot), but I’ve found it very useful to demonstrate

software features by moving the mouse cursor through the same actions as

the user. Instead of just describing something in a help file, you can actually

show the user what to do—and this hack explains how.

I, Robot

To create a mouse animation, you need three things:

1. The ability to move the cursor

2. The start and end points of the animation

3. A way to smoothly interpolate the cursor position

The

java.awt.Robot class has a variety of methods for capturing program

state and controlling the user interface, including

Robot.mouseMove( ), which

allows you to move the mouse cursor programmatically.

The following code is the implementation of a method

moveMouse( ), which

takes three arguments: a starting component, an ending component, and a

duration for the animation (in milliseconds). Because most demonstrations

involve showing the user a particular component, the easiest points to use

are the centers of start and end components. The mouse will smoothly move

from the center of the starting component to the center of the ending one.

We normally think of components as being positioned relative to their par-

ents, but since the

Robot class uses absolute mouse positions, you’ll need to

convert the components to their screen locations:

public void moveMouse(JComponent start, JComponent end,

final int duration) throws Exception {

final Robot robot = new Robot( );

// get middle of start

final Point start_coords = start.getLocationOnScreen( );

start_coords.translate(start.getWidth( )/2,

start.getHeight( )/2);

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// get middle of end

final Point end_coords = end.getLocationOnScreen( );

end_coords.translate(end.getWidth( )/2,

end.getHeight( )/2);

// create interpolation point and offsets

int steps = duration/50;

//Point current = new Point(start_coords);

int distx = (end_coords.x - start_coords.x);

int disty = (end_coords.y - start_coords.y);

// move the mouse over 10 steps

for(int i=1; i<=steps; i++) {

int x = start_coords.x + i*distx/steps;

int y = start_coords.y + i*disty/steps;

robot.mouseMove(x,y);

try { Thread.currentThread( ).sleep(50);

} catch (Exception ex) {}

}

}

This code creates a new Robot and calculates the center positions of the start

and end components using screen coordinates.

steps is the number of

frames required to fill the specified duration. Since each frame will be 1/20

of a second long, the number of frames is the total duration divided by 50

ms.

distx and disty are the distances between the two components in the

horizontal and vertical directions. With these values in hand, it is a simple

matter to interpolate a new position for each frame and then move the

mouse cursor there.

To test the system, you’ll need some sort of a demonstration program. The

code in Example 12-4 creates a fake file browser with a list of directories, a

list of files, and a toolbar with three buttons: Info, New Dir, and Delete. You

can see this in Figure 12-2.

Figure 12-2. Sample program to demonstrate mouse automation

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Chapter 12, Miscellany

#90 Create Demonstrations with the Robot Class

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The demonstration program also contains a Help screen (shown in

Figure 12-3).

Example 12-4. A simple demonstration for the power of Robot

public class AutoMouseHack implements ActionListener {

public JButton info, new_dir, delete;

public void createDemo( ) {

JFrame frame = new JFrame("File Flipper");

String[] dirs = {".","..","build","docs","lib","src","www"};

String[] files = {"build.xml","readme.txt"};

JList dir_list = new JList(dirs);

JList files_list = new JList(files);

JSplitPane split = new JSplitPane(

JSplitPane.HORIZONTAL_SPLIT,

dir_list,files_list);

info = new JButton("Info");

new_dir = new JButton("New Dir");

delete = new JButton("Delete");

JPanel toolbar = new JPanel( );

toolbar.setLayout(new FlowLayout( ));

toolbar.add(info);

toolbar.add(new_dir);

toolbar.add(delete);

frame.getContentPane().setLayout(new BorderLayout( ));

frame.getContentPane( ).add("North",toolbar);

frame.getContentPane( ).add("Center",split);

frame.pack( );

frame.show( );

}

Figure 12-3. Help text