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Java: Example - ToUppercase
Posted on: February 19, 2008 at 12:00 AM
Java: Example - ToUppercase

Java: Example - ToUppercase

Level Introductory
Structure Separate main and GUI files.
ComponentsJButton, JTextField
ContainersJFrame, JPanel
Layouts FlowLayout
Listeners ActionListener as inner class
Other  

Main program

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// ToUpperCase.java Example: Converts text in one field to uppercase in another.
// Fred Swartz, 1999...2004-04-11

import javax.swing.*;

//////////////////////////////////////////////////////////////// ToUpperCase
public class ToUpperCase {
    //================================================================= main
    public static void main(String[] args) {
        JFrame window = new ToUpperCaseGUI();
        window.setTitle("ToUpperCase Example");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.show();  // Same as window.setVisible(true)
    }//end main  
}//end class ToUpperCase

GUI code

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/** ToUpperCaseGUI.java Example: Converts text to uppercase.
    @author Fred Swartz
    @version 2004-04-16
*/

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

///////////////////////////////////////////////////////////// ToUpperCaseGUI
/** GUI (window) for lower to uppercase conversion program. */
public class ToUpperCaseGUI extends JFrame {
    //=================================================== instance variables
    private JTextField _inField  = new JTextField(20);
    private JTextField _outField = new JTextField(20);

    //========================================================== constructor
    /** Creates content pane of the window. */
    public ToUpperCaseGUI() {
        //-- 1. Create or set attributes of components.
        _outField.setEditable(false);  // Don't let user change output.
        JButton toUpperButton = new JButton("To Uppercase");
        
        //--- 2. Add listener(s).
        toUpperButton.addActionListener(new UpperCaseAction());
      
        //--- 3. Create a panel and add components to it
        JPanel p = new JPanel();
        p.setLayout(new FlowLayout());
        p.add(_inField);
        p.add(toUpperButton);
        p.add(_outField);
        
        //-- 4. Set the content panel of window and perform layout.
        this.setContentPane(p);
        this.pack();            // Do layout.
    }//end constructor
    
    //////////////////////////////////////////// inner class UpperCaseAction
    /** Class to hold action listener */
    class UpperCaseAction implements ActionListener {
        /** Actionlistener to convert text to uppercase. */
        public void actionPerformed(ActionEvent e) {
            String data = _inField.getText(); // get the text
            String out  = data.toUpperCase(); // create uppercase text
            _outField.setText(out);           // set output field
        }//end actionPerformed
    }//end inner class UpperCaseAction
    
}//end class ToUpperCaseGUI

Possible extensions

  • Add an "Exit" button that stops the program by calling System.exit(0).
Copyleft 2004 Fred Swartz MIT License, Last update: 2004-04-16
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