How do I initialize a Graphics object in Java?
And you are getting the error that G1 is not initialized. That’s because the variable g1 is never set to anything, and that causes a compile error. To get the code to compile, you would need to, at the very least do this:
Graphics g1 = null; a.paint(g1); However, that obviously won’t help you out too much. You’ll get a NullPointerException when you try to run your code. In order to actually cause your graphics to draw you need to this:
anim1 a=new anim1(); Graphics g1 = anim1.getGraphics(); a.paint(g1); However, that still won’t work because Anim1 will not appear on the screen. To get it to appear on the screen you need something like:
import java.awt.*; import javax.swing.*; import java.applet.*; public class So1 extends Applet < public void paint (Graphics g) < g.drawString("hello",40,30); >public static void main(String ad[]) < JFrame jp1 = new JFrame(); So1 a=new So1 (); jp1.getContentPane().add(a, BorderLayout.CENTER); jp1.setSize(new Dimension(500,500)); jp1.setVisible(true); >> Now notice, we don’t actually call the paint() function ourselves. That’s handled by the awt, which actually picks the graphics context, and calls our paint function for us. If you want, though, you can pass in any graphics object you want and ask it to draw on to that. (so if you want to draw your component onto an image, you can do it)
(note, I changed the classname from anim1 to So1)
Lesson: Getting Started with Graphics
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:
- Draw and fill methods, enabling you to render basic shapes, text, and images
- Attributes setting methods, which affect how that drawing and filling appears
Methods such as setFont and setColor define how draw and fill methods render.
This figure illustrates how these methods relate to graphic objects:
- drawString – For drawing text
g.drawImage(img, 0, 0, width, height, 0, 0, imageWidth, imageHeight, null);
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:
- Whether you want to render the image at the specified location in its original size or scale it to fit inside the given rectangle
- Whether you prefer to fill the transparent areas of the image with color or keep them transparent
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.
Note: If you don’t see the applet running, you need to install at least the Java SE Development Kit (JDK) 7 release.
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.
How do I initialize a Graphics object in Java?
And you are getting the error that G1 is not initialized. That’s because the variable g1 is never set to anything, and that causes a compile error. To get the code to compile, you would need to, at the very least do this:
Graphics g1 = null; a.paint(g1); However, that obviously won’t help you out too much. You’ll get a NullPointerException when you try to run your code. In order to actually cause your graphics to draw you need to this:
anim1 a=new anim1(); Graphics g1 = anim1.getGraphics(); a.paint(g1); However, that still won’t work because Anim1 will not appear on the screen. To get it to appear on the screen you need something like:
import java.awt.*; import javax.swing.*; import java.applet.*; public class So1 extends Applet < public void paint (Graphics g) < g.drawString("hello",40,30); >public static void main(String ad[]) < JFrame jp1 = new JFrame(); So1 a=new So1 (); jp1.getContentPane().add(a, BorderLayout.CENTER); jp1.setSize(new Dimension(500,500)); jp1.setVisible(true); >> Now notice, we don’t actually call the paint() function ourselves. That’s handled by the awt, which actually picks the graphics context, and calls our paint function for us. If you want, though, you can pass in any graphics object you want and ask it to draw on to that. (so if you want to draw your component onto an image, you can do it)
(note, I changed the classname from anim1 to So1)
Solution 2
An applet doesn’t need a main method like a regular Java application does. I’d recommend starting with Sun’s Applets Tutorial. In particular you may want to skip ahead to the section Life Cycle of an Applet to see how the Graphics object is handled within the applet.
Solution 3
All you need to do is simply remove the main method like so:
import java.awt.*; import java.applet.*; public class anim1 extends Applet < public void paint (Graphics g) < g.drawString("Hello",100,100); >>