Java Swing: Creating Graphics Interfaces with JFrame and JPanel - Prof. Travis Doom, Study notes of Computer Science

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Introductory Graphics in JavaIntroductory Graphics in Java

Swing

Jframe objects

Jpanel components

Easy GUI Interfaces:Easy GUI Interfaces: JOptionPane

JOptionPane

import javax.swing.*;public static void main (String[] args) {public static void main (String[] args) {

JOptionPane.showMessageDialog (null, "Hello World!"); } // end method main import javax.swing.*; public static void main (String[] args) {

String filename = JOptionPane.showInputDialog (null,

"Enter filename:");

System.out.println(filename); } //

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Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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// end method main

Swing library:Swing library: JFrame

JFrame

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JF

Ti

tleBar

JFrame

JP

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MenuBar

JPanel ContentPane

JComponent

JComponent

Position determined by:

JComponent

Position determined by:- order in list- layout type

Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

Creating a windowCreating a window

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The JFrame class represents an object that you can display on the screen.

A JFrame holds a title bar menu bar and content pane

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A JFrame holds a title bar, menu bar, and content pane.

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Essentially JFrame is your “standard”/abstract window object.

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You can “nest” components in each other. Syntax is like ArrayList.–

Swing library classes exist for: buttons, menus, radio buttons, labels,text entry areas, check boxes, and other standard GUI widgets.

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After adding components, call methods to layout/display the window.

import javax.swing.*;… JFrame frame = new JFrame();

// Step 1: Make a window frame

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);JPanel contentPane = (JPanel) frame.getContentPane();JLabel label = new JLabel("Hello World!"); // Step 2: Make componentscontentPane.add(label);

// Step 3: Nest components

frame.setSize(300,300);

// Step 4: Display frame

frame.setVisible(true);

Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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Making your own component: extendMaking your own component: extend JPanel

JPanel

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To put your own images on the screen, you need to make a 2D graphicscomponent (a paintable widget).

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The easiest way to do this is to extend the JPanel class and override itsbehavior with the specific behavior of your component

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You only need to override paintComponent()!

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The JFrame calls the paintComponent() method of each of its components whenever itfeels the display needs to be refreshed. It’s a contract. If you want to be a component,then you must have a paintComponent().

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You will never call paintComponent yourself (although you can ask for a repaint()).

import java.awt.*;

// Old library classes, you still need them

import javax.swing.*;

// New library classes, Swing extends AWT

class MyComponent extends Jpanel {

public void paintComponent (Graphics g) {

// your code to tell “g” how to “paint” your object goes here } // end method paintComponent

} //

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Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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// end class

MyComponent

Painting a component with a graphics objectPainting a component with a graphics object^ public void paintComponent (Graphics g) {

g.setColor(Color.red);

// Dip the paintbrush in red//

g.fillRect(20,50,100,100);

// Paint a

100x100 rectangle @ (20,50)

} // end method paintComponentpublic void paintComponent (Graphics g) {

Image image

new ImageIcon("rose

jpg") getImage();

Image image = new ImageIcon("rose.jpg").getImage();g.drawImage(image,2,2,this); } // end method paintComponent

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public void paintComponent (Graphics g) {

g.setColor(Color.black);

// set color black

g.fillRect(0,0,this.getWidth(),this.getHeight()); // paint backgroundint red =

(int) (Math.random() * 255);

int green = (int) (Math.random() * 255);

g int blue =

(int) (Math.random() * 255);

Color randomColor = new Color (red, green, blue);g.setColor(randomColor);

// set RGB color randomly

g.fillOval(70,70,100,100);

// paint 100x100 oval @ (70,70)

} // end method paintComponent

Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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// end method paintComponent

Graphics classesGraphics classes

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The argument to paintComponent is type java.awt.Graphics

g IS A Graphics

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g IS-A Graphics

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In the swing library, g is

actually

an instance of the subclass

javax.swing.Graphics2D which

extends

java.awt.Graphics

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us, the object g has access to Graphics2D methods, but you’ll need to

typecast to get access them!

Graphics

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drawImage()drawLine()drawPolygon()drawRect()

Graphics2Drotate()scale()

()

drawOval()fillRect()setColor()…

()

transform()…

Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

Simple animation: Test ClassSimple animation: Test Class

import javax.swing.*;public class Main {

public static void pause () {

try {

Thread.sleep (5);

// wait 5ms

} catch (Exception e) {

e.printStackTrace (); }} } // end method pausepublic static void main (String[] args) {

JFrame frame = new JFrame();frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);frame.setSize (300,300);frame.setVisible (true);BouncingBallPanel ballPanel = new BouncingBallPanel();frame.getContentPane ().add (ballpanel);while (true) {while (true) {

pause();ballPanel.move();ballPanel.repaint(); } } //

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Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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// end method main

} // end class Main

Simple animation: Bouncing BallSimple animation: Bouncing Ball

import javax.swing.;import java.awt.;public class BouncingBallPanel extends JPanel {

int x = 100; int y = 100; int ballSize = 20; int run = 1; int rise = 3;public void paintComponent (Graphics g) {

g.setColor(Color.black);g^

fillRect (

0

getWidth() getHeight());

g.fillRect (0,0,getWidth(),getHeight());g.setColor(Color.red);g.fillOval(x,y,ballSize,ballSize);

} // method paintComponent (required!)public void move () {

if (x < 0 || x > getWidth() -

ballSize) {

run = -run; } if (y < 0 || y > getHeight() - ballSize) {

rise =

-rise;

rise

rise;

} x += run;y += rise;

} // end method move } //

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Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II

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// end class BouncingBallPanel

Example: Bouncing ballsExample: Bouncing balls

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How can we add multiple balls?

How can we allow differentiation? (color speed initial position etc)

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How can we allow differentiation? (color, speed, initial position, etc)

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How can we detect collisions and have the balls respond appropriately?

Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

CS 241Computer Programming II