1. Frame Class
Lecture 11
Naveen Kumar

2. A Simple Program
import javax.swing.JFrame;
import javax.swing.JLabel;
class HelloWorldFrame extends JFrame
{
public static void main(String args[])
{ JFrame f = new JFrame();
f. setSize(100, 100);
JLabel X = new JLabel("Hello World");
f.add(X);
f.setVisible(true);
} }
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3. A Simple Program
import javax.swing.JFrame;
import javax.swing.JLabel;
class HelloWorldFrame extends JFrame
{
public static void main(String args[])
{ new HelloWorldFrame();
}
HelloWorldFrame()
{ JLabel X = new JLabel("Hello World");
add(X);
setSize(100, 100);
setVisible(true);
} }3
Problem: on window close cursor will not go
on C: prompt

4. Frame Windows
 The JFrame class JFrame frame = new JFrame();
 frame.setSize(300, 400);
frame.setTitle("An Empty Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
 import javax.swing.*;
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5. Frame program
import javax.swing.*;
public class frame
{
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.setSize(300, 400);
frame.setTitle("An Empty Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
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6. Drawing Shapes
 paintComponent: called whenever the component
needs to be repainted: (to create component)
public class frame1 extends JComponent
{
public void paintComponent(Graphics g)
{
// Recover Graphics2D
Graphics2D g2 = (Graphics2D) g;
. . .
}
}
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7. Drawing Shapes
 Graphics class lets you manipulate the graphics state
(such as current color)
 Graphics2D class has methods to draw shape objects
 Use a cast to recover the Graphics2D object from the
Graphics parameter
Rectangle box = new Rectangle(5, 10, 20, 30);
g2.draw(box);
 java.awt package7

8. Rectangle Drawing Program
 frame1: its paintComponent method produces the drawing
 frame: its main method constructs a frame and a frame1, adds the
component to the frame, and makes the frame visible
– Construct a frame
– Construct an object of your component class:
frame1 component = new frame1();
– Add the component to the frame
frame.add(component);
– Make the frame visible frame.setVisible(true);
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9. An example (produce a drawing
with two boxes)
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JComponent; /** A component that draws two rectangles. */
public class frame1 extends JComponent {
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g; // Recover Graphics2D
Rectangle box = new Rectangle(5, 10, 20, 30); // Construct a rectangle and
g2.draw(box); // draw it
box.translate(15, 25); // Move rectangle 15 units to the right and 25 units down
g2.draw(box); // Draw moved rectangle
} }
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10. Create frame and add drawing
import javax.swing.JFrame;
public class frame {
public static void main(String[] args) {
JFrame frame = new JFrame();
final int FRAME_WIDTH = 300;
final int FRAME_HEIGHT = 400;
frame.setSize(FRAME_WIDTH,FRAME_HEIGHT);
frame.setTitle("Two rectangles");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame1 component = new frame1();
frame.add(component);
frame.setVisible(true);
} }10

11. Applets
 This is almost the same outline as for a component, with two minor
differences:
– You extend JApplet, [not JComponent]
– You place the drawing code inside the paint method, not inside
paintComponent
 To run an applet, you need an HTML file with the applet tag
 You view applets with the appletviewer
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12. JApplet
/* <APPLET CODE="frameapplet.class" WIDTH=350 HEIGHT=200>
</APPLET>*/
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JApplet; /** An applet that draws two rectangles. */
public class frameapplet extends JApplet
{ public void paint(Graphics g)
{ Graphics2D g2 = (Graphics2D) g;
Rectangle box = new Rectangle(5, 10, 20, 30);
g2.draw(box);
box.translate(15, 25);
g2.draw(box);
} }
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13. Graphical Shapes
 Rectangle, Ellipse2D.Double, and Line2D.Double describe graphical
shapes
 We won't use the .Float classes
 These classes are inner classes–doesn't matter to us except for the
import statement:
import java.awt.geom.Ellipse2D; // no .Double
 Must construct and draw the shape
Ellipse2D.Double ellipse = new Ellipse2D.Double(x, y, width, height);
g2.draw(ellipse);
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14. Drawing Lines
To draw a line:
 Line2D.Double segment = new Line2D.Double(x1, y1, x2, y2);
or
 Point2D.Double from = new Point2D.Double(x1, y1);
Point2D.Double to = new Point2D.Double(x2, y2);
Line2D.Double segment = new Line2D.Double(from, to);
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15. Self Check
 Give instructions to draw a circle with center (100,100) and radius 25
 Give instructions to draw a letter "V" by drawing two line segments
 Give instructions to draw a string consisting of the letter "V"
Answers
 g2.draw(new Ellipse2D.Double(75, 75, 50, 50);
 Line2D.Double segment1 = new Line2D.Double(0, 0, 10, 30);
g2.draw(segment1);
Line2D.Double segment2 = new Line2D.Double(10, 30, 20, 0);
g2.draw(segment2);
 g2.drawString("V", 0, 30);
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Upper-left corner, Width , Height

16. Colors
 Standard colors Color.BLUE, Color.RED, Color.PINK etc.
 Specify red, green, blue between 0.0F and 1.0F
 Color magenta = new Color(1.0F, 0.0F, 1.0F); // F = float/real
Set color in graphics context
 g2.setColor(magenta);
Color is used when drawing and filling shapes
 g2.fill(rectangle); // filled with current color
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17. Self Check
 What are the RGB color values of Color.BLUE?
 How do you draw a yellow square on a red background?
Answers
 0.0F, 0.0F, and 0.1F
 First fill a big red square, then fill a small yellow square inside:
g2.setColor(Color.RED);
g2.fill(new Rectangle(0, 0, 200, 200));
g2.setColor(Color.YELLOW);
g2.fill(new Rectangle(50, 50, 100, 100));
Note: Use import java.awt.Color;
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18. Drawing Graphical Shapes
 Rectangle leftRectangle
= new Rectangle(100, 100, 30, 60);
Rectangle rightRectangle
= new Rectangle(160, 100, 30, 60);
Line2D.Double topLine
= new Line2D.Double(130, 100, 160, 100);
Line2D.Double bottomLine
= new Line2D.Double(130, 160, 160, 160);
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19. Reading Text Input
 A graphical application can obtain input by displaying a
JOptionPane
 The showInputDialog method displays a prompt and
waits for user input
 The showInputDialog method returns the string that the
user typed
String input = JOptionPane.showInputDialog("Enter x");
double x = Double.parseDouble(input);
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20. An Example
import java.awt.Color; import javax.swing.Jframe;
import javax.swing.JOptionPane; import javax.swing.JComponent;
public class ColorViewer {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setSize(300,400); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
String input; // Ask the user for red, green, blue values
input = JOptionPane.showInputDialog("red:");
double red = Double.parseDouble(input);
input = JOptionPane.showInputDialog("green:");
double green = Double.parseDouble(input);
input = JOptionPane.showInputDialog("blue:");
double blue = Double.parseDouble(input);
Color fillColor = new Color( (float) red, (float) green, (float) blue);
Square component = new Square (fillColor);
frame.add(component); frame.setVisible(true); } }20

21. Example cont.
import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Rectangle
public class Square extends JComponent {
private Color fillColor;
public Square (Color aColor) { fillColor = aColor; }
public void paintComponent(Graphics g) {
Graphics2D g2 = (Graphics2D) g; // Select color into graphics context
g2.setColor(fillColor); // Const and fill a square whose center is center of the window
Rectangle square = new Rectangle(20,40,100,100);
g2.fill(square); }
}
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