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Easy Learn Java: Programming Articles, Examples and Tips - Page 322


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Java: Example - KeyDemo

Go to all tips in Java Notes by Fred Swartz

This program doesn't do anything useful, but it does illustrate handling regular characters, virtual, and modifier keys.

A standard main program

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// KeyDemo.java - Demonstrates handling three kinds of keys:
import javax.swing.*;
/** Demonstrates handling of different types of keys:
    virtual keys (arrows), modifiers (shift), and characters.
    @author Fred Swartz
    @version 2004-05-06
*/
public class KeyDemo extends JFrame {
    public static void main(String[] args) {
        JFrame window = new KeyDemoGUI();
        window.setDefaultCloseOperation(EXIT_ON_CLOSE);
        window.setVisible(true);
    }
}//endclass KeyDemo

A standard subclass of JFrame to build the GUI

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// KeyDemoGUI.java - JFrame subclass
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
//////////////////////////////////////////////////////////////// KeyDemoGUI
/** JFrame subclass for KeyDemo GUI.
    virtual keys (arrows), and characters.
    @author Fred Swartz
    @version 2004-05-06
*/
public class KeyDemoGUI extends JFrame {
    MovingTextPanel drawing;

    //==========================================================constructor
    public KeyDemoGUI() {
        drawing = new MovingTextPanel();
        this.getContentPane().setLayout(new BorderLayout());
        JLabel instructions = new JLabel("
  • Type text.
  • " + "
  • Use arrow keys to move text.
  • " + "
  • Press shift arrows to move faster.
  • "); this.getContentPane().add(instructions, BorderLayout.NORTH); this.getContentPane().add(drawing, BorderLayout.CENTER); this.setTitle("KeyDemo"); this.pack(); drawing.requestFocus(); // Give the panel focus. }//end constructor }//endclass KeyDemoGUI

A subclass of JPanel that has a KeyListener

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// MovingTextPanel.java - Demonstrates handling three kinds of keys:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

///////////////////////////////////////////////////////// class DrawingPanel
/** Define a new panel to draw on, therefore it has a paintComponent method.
    This class implements KeyListener, altho the listeners don't really 
    have to be inside this class.
    This class displays any characters that are typed, and handles
    virtual keys (arrows) and modifiers (shift) to move the text.
    @author Fred Swartz
    @version 2004-05-06
*/
class MovingTextPanel extends JPanel implements KeyListener {
    //===================================================== field variables
    String display = ""; // Initial string to display
    private int x = 50;  // Initial coordinates of string
    private int y = 50;
    
    private Font biggerFont = new Font("sansserif", Font.PLAIN, 24);
    private int speed = 2; // number of pixels to move
    
    //========================================================= constructor
    public MovingTextPanel() {
        this.setBackground(Color.white);
        this.setFont(biggerFont);
        this.setPreferredSize(new Dimension(300, 200));
        this.addKeyListener(this);  // This class has its own key listeners.
        this.setFocusable(true);    // Allow panel to get focus
    }//endconstructor

    //======================================================= paintComponent
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawString(display, x, y);
    }//endmethod paintComponent

    //==================================================== keyTyped listener
    /** This listener is called for character keys. */
    public void keyTyped(KeyEvent kevt) {
        //System.out.println("keyTyped");
        char c = kevt.getKeyChar();
        if (c == '') { // if this is a backspace
            if (display.length() > 0) {  // remove last character
                display = display.substring(0, display.length()-1);
            }
        } else {
            display += c;
        }
        this.repaint();
    }//endmethod keyTyped

    //================================================== keyPressed listener
    /** This listener is called for both character and non-character keys. */
    public void keyPressed(KeyEvent e) {
        // Check the shift key, and do 10x the movement if the
        // shift key is down when the arrow keys are pressed.
        // Altho keyPressed is called for normal characters, they
        // are ignored here and handled in keyTyped.
        if (e.isShiftDown()) {
            speed = 10;
        } else {
            speed = 2;
        }        
        
        //-- Process arrow "virtual" keys
        switch (e.getKeyCode()) {
            case KeyEvent.VK_LEFT : x -= speed; x = Math.max(x, 0);   break;
            case KeyEvent.VK_RIGHT: x += speed; x = Math.min(x, 300); break;
            case KeyEvent.VK_UP   : y -= speed; y = Math.max(y, 0);   break;
            case KeyEvent.VK_DOWN : y += speed; y = Math.min(y, 200); break;
        }
        
        speed = 2;       // Restore speed to its default value
            
        this.repaint();  // Display the changes.
    }//endmethod keyPressed

    //------------------------------------------------- keyReleased listener
    public void keyReleased(KeyEvent ke) {}  // Ignore.
}//endclass MovingTextPanel


3 comments | Printer Friendly Page  Send to a Friend | Score: 0
Posted by jalex on Wednesday, March 16, 2005 (00:00:00) (3500 reads)

Java: Presentation-Model Structure

Go to all tips in Java Notes by Fred Swartz

The single most important structure in a program is to separate the user interface from the model (business logic, domain, ...). This provides a huge improvement in simplicity, altho at first it may not appear so. Program enhancements and maintenance are much simpler with this structure.

A further separation can be found in the next example which separates the View (displaying information) from the Controller (processing user interactions) -- the MVC pattern. However, for most applications, you will probably get most of the benefit without some of the complications by simply sticking to the Presentation-Model organization that is shown here.

Main class

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// structure/presentation-model/CalcV3.java 
//   Calculator with separation of presentation and model.
// Fred Swartz -- December 2004

// Program Organization: Separate View+Controller and Model

import javax.swing.*;

public class CalcV3 {
    public static void main(String[] args) {     
        JFrame presentation = new CalcViewController();
        presentation.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        presentation.setTitle("Simple Calc - Presentation-Model");
        presentation.setVisible(true);
    }
}

The Presentation (GUI, View+Controller, ...)

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// structure/presentation-model/CalcViewController.java
// Fred Swartz - December 2004

// GUI Organization - GUI independent of model.
// 
//     GUI subclasses JFrame and builds it in the constructor.
//
//     The GUI creates a calculator model object, but knows nothing 
//     about the internal implementation of the calculator.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class CalcViewController extends JFrame {
    //... Constants
    private static final String INITIAL_VALUE = "1";
    
    //... The Model.
    private CalcModel  m_logic;
    
    //... Components
    private JTextField m_userInputTf = new JTextField(5);
    private JTextField m_totalTf     = new JTextField(20);
    private JButton    m_multiplyBtn = new JButton("Multiply");
    private JButton    m_clearBtn    = new JButton("Clear");
    
    /** Constructor */
    CalcViewController() {
        //... Set up the logic
        m_logic = new CalcModel();
        m_logic.setValue(INITIAL_VALUE);
        
        //... Initialize components
        m_totalTf.setText(m_logic.getValue());
        m_totalTf.setEditable(false);
        
        //... Layout the components.        
        JPanel content = new JPanel();
        content.setLayout(new FlowLayout());
        content.add(new JLabel("Input"));
        content.add(m_userInputTf);
        content.add(m_multiplyBtn);
        content.add(new JLabel("Total"));
        content.add(m_totalTf);
        content.add(m_clearBtn);
        
        //... finalize layout
        this.setContentPane(content);
        this.pack();
        
        //... Set button listeners.
        m_multiplyBtn.addActionListener(new MultiplyListener());
        m_clearBtn.addActionListener(new ClearListener());
    }//end constructor
    
    
    ////////////////////////////////////////// inner class MultiplyListener
    /** When a mulitplication is requested.
     *  1. Get the user input number.
     *  2. Call the model to mulitply by this number.
     *  3. Get the result from the Model.
     *  4. Set the Total textfield to this result.
     * If there was an error, display it in a JOptionPane.
     */
    class MultiplyListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String userInput = "";
            try {
                userInput = m_userInputTf.getText();
                m_logic.multiplyBy(userInput);
                m_totalTf.setText(m_logic.getValue());
            } catch (NumberFormatException nfex) {
                JOptionPane.showMessageDialog(CalcViewController.this, 
                                      "Bad input: '" + userInput + "'");
            }
        }
    }//end inner class MultiplyListener
    
    
    //////////////////////////////////////////// inner class ClearListener
    /**  1. Reset model.
     *   2. Put model's value into Total textfield.
     */    
    class ClearListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            m_logic.reset();
            m_totalTf.setText(m_logic.getValue());
        }
    }// end inner class ClearListener

}

The Model (Logic, ...)

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// structure/presentation-model/CalcModel.java
// Fred Swartz - December 2004
// Model
//     This model is completely independent of the user interface.
//     It could as easily be used by a command line or web interface.

import java.math.BigInteger;

public class CalcModel {
    //... Constants
    private static final String INITIAL_VALUE = "0";
    
    //... Member variable defining state of calculator.
    private BigInteger m_total;  // The total current value state.
    
    //========================================================== constructor
    /** Constructor */
    CalcModel() {
        reset();
    }
    
    //================================================================ reset
    /** Reset to initial value. */
    public void reset() {
        m_total = new BigInteger(INITIAL_VALUE);
    }
    
    //=========================================================== multiplyBy
    /** Multiply current total by a number.
    *@param operand Number (as string) to multiply total by.
    */
    public void multiplyBy(String operand) {
        m_total = m_total.multiply(new BigInteger(operand));
    }
    
    //============================================================= setValue
    /** Set the total value. 
    *@param value New value that should be used for the calculator total. 
    */
    public void setValue(String value) {
        m_total = new BigInteger(value);
    }
    
    //============================================================= getValue
    /** Return current calculator total. */
    public String getValue() {
        return m_total.toString();
    }
}


6 comments | Printer Friendly Page  Send to a Friend | Score: 0
Posted by jalex on Tuesday, March 15, 2005 (00:00:00) (4229 reads)

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