The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
The Java 2D API is powerful and complex. However, the vast majority of uses for the Java 2D API utilize a small subset of its capabilities encapsulated in the java.awt.Graphics
class. This lesson covers the most common needs of applications developers. Less common needs are described later in the
Advanced topics in the Java 2D API.
Most methods of the
Graphics
class can be divided into two basic groups:
Methods such as setFont
and setColor
define how draw and fill methods render.
This figure illustrates how these methods relate to graphic objects:
Drawing methods include:
drawString
– For drawing text
g.drawString("Hello", 10, 10);
drawImage
– For drawing images
g.drawImage(img, 0, 0, width, height, 0, 0, imageWidth, imageHeight, null);
drawLine
, drawArc
, drawRect
, drawOval
, drawPolygon
– For drawing geometric shapes
g2.draw(new Line2D.Double(0, 0, 30, 40));
Depending on your current need, you can choose one of several methods in the Graphics
class based on the following criteria:
Fill methods apply to geometric shapes and include fillArc
, fillRect
, fillOval
, fillPolygon
.
Whether you draw a line of text or an image, remember that in 2D graphics every point is determined by its x and y coordinates. All of the draw and fill methods need this information which determines where the text or image should be rendered.
For example, to draw a line, an application calls the following:
java.awt.Graphics.drawLine(int x1, int y1, int x2, int y2)
In this code (x1, y1) is the start point of the line, and (x2, y2) is the end point of the line.
So the code to draw a horizontal line is as follows:
Graphics.drawLine(20, 100, 120, 100);
The demo below accumulates all mentioned techniques. Move the slider to display various weather types.
The WeatherWizard
demo uses the JSlider
component as well as various graphics capabilities to generate and display a specified weather type.
For more information about the JSlider
class see the
How to Use Sliders section of the Swing Tutorial.
The paint
method of the WeatherPainter
class implements graphics features. The following code draws an image determined by using the setupWeatherReport()
method.
... origComposite = g2.getComposite(); if (alpha0 != null) g2.setComposite(alpha0); g2.drawImage(img0, 0, 0, size.width, size.height, 0, 0, img0.getWidth(null), img0.getHeight(null), null); if (img1 != null) { if (alpha1 != null) g2.setComposite(alpha1); g2.drawImage(img1, 0, 0, size.width, size.height, 0, 0, img1.getWidth(null), img1.getHeight(null), null); } ...
The setFont
and drawString
methods render the temperature and the weather condition.
... // Freezing, Cold, Cool, Warm, Hot, // Blue, Green, Yellow, Orange, Red Font font = new Font("Serif", Font.PLAIN, 36); g.setFont(font); String tempString = feels + " " + temperature+"F"; FontRenderContext frc = ((Graphics2D)g).getFontRenderContext(); ... g.setColor(textColor); int xTextTemp = rX-(int)boundsTemp.getX(); int yTextTemp = rY-(int)boundsTemp.getY(); g.drawString(tempString, xTextTemp, yTextTemp); int xTextCond = rX-(int)boundsCond.getX(); int yTextCond = rY-(int)boundsCond.getY() + (int)boundsTemp.getHeight(); g.drawString(condStr, xTextCond, yTextCond);
The fillRect
method allows you to draw a rectangle filled with the specified color.
... Rectangle2D boundsTemp = font.getStringBounds(tempString, frc); Rectangle2D boundsCond = font.getStringBounds(condStr, frc); int wText = Math.max((int)boundsTemp.getWidth(), (int)boundsCond.getWidth()); int hText = (int)boundsTemp.getHeight() + (int)boundsCond.getHeight(); int rX = (size.width-wText)/2; int rY = (size.height-hText)/2; g.setColor(Color.LIGHT_GRAY); g2.fillRect(rX, rY, wText, hText); ...
Try to modify the WeatherWizard
demo to alter the graphical content. For example, use the fillRoundRect
method instead of fillRect
or apply another font size in the setFont
method. Find the complete code for this applet in the
WeatherWizard.java
file. The demo also requires the following images:
weather-cloud.png
,
weather-rain.png
,
weather-snow.png
, and
weather-sun.png
located in the images
directory.