Painting Shapes

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Trail: Creating a GUI with JFC/Swing
Lesson: Working with Graphics

Painting Shapes

The Graphics class defines methods for painting the following kinds of shapes:

Lines (drawLine)
Rectangles (drawRect and fillRect)
Raised or lowered rectangles (draw3DRect and fill3DRect)
Round-edged rectangles (drawRoundRect and fillRoundRect)
Ovals (drawOval and fillOval)
Arcs (drawArc and fillArc)
Polygons (drawPolygon, drawPolyline, and fillPolygon)
Here is an example of painting the outline of a rectangle:
g.drawRect(x, y, rectWidth - 1, rectHeight - 1);
Here is an example of painting a filled rectangle of the same size.
g.fillRect(x, y, rectWidth, rectHeight);
Note that for the drawRect method, you must specify one pixel less than the desired width and height. This is because the painting system draws lines just below the specified rectangle, instead of within the specified rectangle. The same rule of specifying one less than the desired width applies to other drawXxx methods, such as draw3DRect. For the fillXxx methods, on the other hand, you specify exactly the desired width and height in pixels.

Java^TM 2 Note: If you are using Java 2 (JDK^TM 1.2), you can use the new Java^TM 2D API, which allows you to create virtually any kind of geometric shape and to specify line styles, line sizes, and fancy fill patterns. To learn how to take advantage of this new functionality, see the 2D Graphics trail. In particular, see the Stroking and Filling Graphics Primitives and Shapes lessons, which present a Java 2D implementation of the program presented in Example 2: A Shape Sampler.

Example 1: Simple Rectangle Painting

Here's a picture of a program that's almost the same as the CoordinatesDemo program shown in The Coordinate System. Like CoordinatesDemo, this program paints a rectangle wherever the user clicks. However, this program's rectangle is larger and has a yellow fill. Here is a picture of its GUI:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.
The program features two components. The largest is a custom component implemented by a class named RectangleArea. It paints the beveled border and everything inside it, including the yellow rectangle. The other component is a label that appears at the bottom of the GUI, under the custom component. The label describes the program's current state.
You can find the program's code in RectangleDemo.java. Here is the painting-related code for the custom component:
class RectangleArea extends JPanel {
    ...
    int rectWidth = 50;
    int rectHeight = 50;
    ...
    public RectangleArea(...) {
        ...
        Border raisedBevel = BorderFactory.createRaisedBevelBorder();
        Border loweredBevel = BorderFactory.createLoweredBevelBorder();
        Border compound = BorderFactory.createCompoundBorder
                              (raisedBevel, loweredBevel);
        setBorder(compound);
        ...
    }
    ...
    public void paintComponent(Graphics g) {
        super.paintComponent(g);  //paint background

        //Paint a filled rectangle at user's chosen point.
        if (point != null) {
            g.drawRect(point.x, point.y,
                       rectWidth - 1, rectHeight - 1);
            g.setColor(Color.yellow);
            g.fillRect(point.x + 1, point.y + 1,
                       rectWidth - 2, rectHeight - 2);

            controller.updateLabel(point);
        }
    }
}
The component's implementation of paintComponent uses the fillRect method to paint a 50-by-50-pixel rectangle outline, filled with a 48-by-48-pixel yellow rectangle. Note the differences in the arguments specified to drawRect and fillRect.
Note: It's perfectly legal to specify x, y, height, or width values that are negative or cause a result larger than the painting area. Values outside the painting area don't matter too much because they're clipped to the painting area. You just won't see part of the shape. Negative height or width results in the shape not being painted at all.
For a little more information about this example, see The Coordinate System, which features the CoordinatesDemo example on which RectangleDemo is based.

Example 2: A Shape Sampler

The ShapesDemo program demonstrates all the shapes you can draw and fill, using API supported with both JDK 1.1 and Java 2. Here is a picture of its GUI:

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

Note: Unless the default font is very small, some of the strings displayed by ShapesDemo overlap with other strings. A fix for this problem is demonstrated in Getting Information About a Font: FontMetrics.

You can find the code for the entire program in ShapesDemo.java. The following snippet is just the code that paints the geometric shapes, where the bold lines are the actual invocations of painting methods. The rectHeight and rectWidth variables specify the size in pixels of the rectangle that contains the shape to be drawn. The x and y variables are changed for every shape, so that the shapes aren't painted on top of each other. The bg and fg variables are Color objects that specify the component's background and foreground colors, respectively.
Color fg3D = Color.lightGray;
...
// drawLine(x1, y1, x2, y2) 
g.drawLine(x, y+rectHeight-1, x + rectWidth, y);
...
// drawRect(x, y, w, h) 
g.drawRect(x, y, rectWidth, rectHeight);
...
// draw3DRect(x, y, w, h, raised) 
g.setColor(fg3D);
g.draw3DRect(x, y, rectWidth, rectHeight, true);
g.setColor(fg);
...
// drawRoundRect(x, y, w, h, arcw, arch) 
g.drawRoundRect(x, y, rectWidth, rectHeight, 10, 10);
...
// drawOval(x, y, w, h) 
g.drawOval(x, y, rectWidth, rectHeight);
...
// drawArc(x, y, w, h, startAngle, arcAngle) 
g.drawArc(x, y, rectWidth, rectHeight, 90, 135);
...
// drawPolygon(xPoints, yPoints, numPoints) 
int x1Points[] = {x, x+rectWidth, x, x+rectWidth};
int y1Points[] = {y, y+rectHeight, y+rectHeight, y};
g.drawPolygon(x1Points, y1Points, x1Points.length); 
...
// drawPolyline(xPoints, yPoints, numPoints) 
// Note: drawPolygon would close the polygon.
int x2Points[] = {x, x+rectWidth, x, x+rectWidth};
int y2Points[] = {y, y+rectHeight, y+rectHeight, y};
g.drawPolyline(x2Points, y2Points, x2Points.length); 
...
// fillRect(x, y, w, h)
g.fillRect(x, y, rectWidth, rectHeight);
...
// fill3DRect(x, y, w, h, raised) 
g.setColor(fg3D);
g.fill3DRect(x, y, rectWidth, rectHeight, true);
g.setColor(fg);
...
// fillRoundRect(x, y, w, h, arcw, arch)
g.fillRoundRect(x, y, rectWidth, rectHeight, 10, 10);
...
// fillOval(x, y, w, h)
g.fillOval(x, y, rectWidth, rectHeight);
...
// fillArc(x, y, w, h, startAngle, arcAngle) 
g.fillArc(x, y, rectWidth, rectHeight, 90, 135);
...
// fillPolygon(xPoints, yPoints, numPoints) 
int x3Points[] = {x, x+rectWidth, x, x+rectWidth};
int y3Points[] = {y, y+rectHeight, y+rectHeight, y};
g.fillPolygon(x3Points, y3Points, x3Points.length); 
...

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