combining two strings using java

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

//////////////////////////////////////////////////////////////// CombineName
public class CombineName extends JFrame {
    //=================================================== instance variables
    private JTextField _fNameTf        = new JTextField(8);
    private JTextField _lNameTf        = new JTextField(8);
    private JTextField _combinedNameTf = new JTextField(14);
    
    //================================================================= main
    public static void main(String[] args) {
        JFrame window = new CombineName();   // Create window.
    }
    
    //========================================================== constructor
    public CombineName() {
        //... 1. Create or set attributes of components.
        _combinedNameTf.setEditable(false);  // Don't let user change output.
        JButton combineBtn = new JButton("Combine");
        
        //... 2. Add listener(s).
        combineBtn.addActionListener(new CombineAction());
        
        //... 3. Create a panel, set layout, and add components to it.
        JPanel content = new JPanel();
        content.setLayout(new FlowLayout());
        content.add(new JLabel("First"));
        content.add(_fNameTf);
        content.add(new JLabel("Last"));
        content.add(_lNameTf);
        content.add(combineBtn);
        content.add(new JLabel("Combined Name"));
        content.add(_combinedNameTf);
        
        //... 4. Set the content panel of window and perform layout.
        this.setContentPane(content);
        this.setTitle("CombineName Example");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();                       // Do layout.
        this.setLocationRelativeTo(null);  // Center window.
        this.setVisible(true);
    }
    
    ///////////////////////////////////// inner listener class CombineAction
    class CombineAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //... Get text from the text fields, combine, set text.
            //    Please make this program do something interesting.
            String first = _fNameTf.getText();
            String last  = _lNameTf.getText();
            String combined = last + ", " + first;  // Trivial logic!!!
            _combinedNameTf.setText(combined);
        }
    }
}

Lower case to Upper case conversion in java

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

//////////////////////////////////////////////////////////////// ToUpperCase
public class ToUpperCase extends JApplet {

    //=================================================== instance variables
    private JTextField _inField  = new JTextField(20);
    private JTextField _outField = new JTextField(20);

    //================================================================= main
    public static void main(String[] args) {
        JFrame window = new JFrame();
        window.setTitle("ToUpperCase Example");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        //... JApplet works fine as content pane in a window!
        window.setContentPane(new ToUpperCase());

        window.pack();                       // Layout components.
        window.setLocationRelativeTo(null);  // Center window.
        window.setVisible(true);
    }

    //================================================== applet constructor
    public ToUpperCase() {
        //... Create or set attributes of components.
        _outField.setEditable(false);    // Don't let user change output.
        JButton toUpperButton = new JButton("To Uppercase");

        //... Add listener to button.
        toUpperButton.addActionListener(new UpperCaseAction());

        //... Add components directly to applet.  Don't need content pane.
        setLayout(new FlowLayout());
        add(_inField);
        add(toUpperButton);
        add(_outField);
    }

    /////////////////////////////////// inner listener class UpperCaseAction
    class UpperCaseAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //... Convert text in one textfield to uppercase in another.
            String data = _inField.getText();  // Get the text
            String out  = data.toUpperCase();  // Create uppercase version.
            _outField.setText(out);            // Set output field
        }
    }
}

Detecting Extension Filename in JAVA

import javax.swing.*;

public class FileExt {

    public static void main(String[] args) {
        //... Declare local variables.
        String fileName;   // The file name the user entered.
        String extension;  // The extension.

        //... Input a file name and remove whitespace.
        fileName = JOptionPane.showInputDialog(null, "Enter file name.");
        fileName = fileName.trim();

        //... Find the position of the last dot.  Get extension.
        int dotPos = fileName.lastIndexOf(".");
        extension = fileName.substring(dotPos);

        //... Output extension.
        JOptionPane.showMessageDialog(null, "Extension is " + extension);
    }
}

Capitalizae charecters using java

import javax.swing.*;

public class Capitalize2 {

    public static void main(String[] args) {
        //.. Input a word
        String inputWord = JOptionPane.showInputDialog(null, "Enter a word");

        //.. Process - Separate word into parts, change case, put together.
        String firstLetter = inputWord.substring(0,1);  // Get first letter
        String remainder   = inputWord.substring(1);    // Get remainder of word.
        String capitalized = firstLetter.toUpperCase() + remainder.toLowerCase();

        //.. Output the result.
        JOptionPane.showMessageDialog(null, capitalized);
    }
}

Km to Miles conversion using swing

import javax.swing.*;

public class KmToMiles {
    //============================================================ constants
    private static final double MILES_PER_KILOMETER = 0.621;   

    //================================================================= main
    public static void main(String[] args) {                        //Note 1
        //... Local variables
        String kmStr;    // String km before conversion to double.
        double km;       // Number of kilometers.
        double mi;       // Number of miles.

        //... Input
        kmStr = JOptionPane.showInputDialog(null, "Enter kilometers.");
        km = Double.parseDouble(kmStr);

        //... Computation
        mi = km * MILES_PER_KILOMETER;

        //... Output
        JOptionPane.showMessageDialog(null, km + " kilometers is " + mi + " miles.");
    }
}