CS18000: Problem Solving and Object-Oriented Programming - Simple GUIs

Simple Graphical User Interfaces

  • Text-Based Interface vs. GUI

    • Text-Based Interface:

    • User enters data via keyboard.

    • Outputs displayed in a terminal window.

    • Graphical User Interface (GUI):

    • Displays controls or widgets in a window.

    • User interacts with these controls, and the program responds to events.

Dialog Concepts

  • Prerequisites: Application must be running on a Java Virtual Machine (JVM) with a configured window system.

  • Java dialogs are modal, meaning they block the application code from running until the user responds.

  • Java GUI components adapt to the “Look and Feel” of the local system.

JOptionPane Class

  • Purpose: A core class in Java for creating modal dialogs.

  • Import Statement: import javax.swing.JOptionPane;

  • Common Static Methods:

    • showMessageDialog

    • showInputDialog

    • showConfirmDialog

    • showOptionDialog

Common Arguments for JOptionPane

  • Location: Where the dialog appears on the screen (null centers it).

  • Message: String, icon, or HTML content displayed in the dialog.

  • Message Type: Affects the look and feel and icon displayed.

  • Option Type: Specifies default buttons included.

  • Icon: Custom icon to replace the default icon.

  • Title: String for the dialog window heading.

  • Initial Value: Default value for certain input fields.

    • Many arguments are optional and can use defaults.

Message Type Parameter

  • Determines the icon displayed and varies by system look and feel.

  • Possible Values:

    • JOptionPane.PLAIN_MESSAGE (-1)

    • JOptionPane.ERROR_MESSAGE (0)

    • JOptionPane.INFORMATION_MESSAGE (1)

    • JOptionPane.WARNING_MESSAGE (2)

    • JOptionPane.QUESTION_MESSAGE (3)

JOptionPane Methods

  • showMessageDialog:

    • Displays a message to the user.

    • This is a void method (only displays, does not return any value).

  • showConfirmDialog:

    • Prompts for user confirmation (e.g., “Yes”, “No”, “Cancel”).

    • Method returns an integer indicating the user's selection.

    • Default options include:

    • JOptionPane.YES_NO_OPTION

    • JOptionPane.YES_NO_CANCEL_OPTION

    • JOptionPane.OK_CANCEL_OPTION

    • Possible return values:

    • JOptionPane.YES_OPTION (0)

    • JOptionPane.NO_OPTION (1)

    • JOptionPane.CANCEL_OPTION (2)

    • JOptionPane.CLOSED_OPTION (-1)

  • showInputDialog:

    • Requests user input and returns a String.

    • Allows for free typing or selection from a list (dropdown).

    • Can create dropdowns using an array of Strings and specify an initial value.

  • showOptionDialog:

    • More configurable, allowing for different button arrangements.

    • Returns the index of the button selected by the user.

    • Accepts multiple parameters (e.g., message, title, icons).

Codon Extractor Example

  • Problem: Write a program to read a DNA sequence and display the codons within it.

  • Definitions:

    • DNA Sequence: Sequence of characters in ACGT.

    • Codon: Sequence of three characters in the DNA sequence.

  • Algorithm Steps:

    1. Prompt user for DNA.

    2. Validate input.

    3. Break DNA into 3-character chunks.

    4. Repeat until the user indicates they are done.

CodonExtractor Class Example

  • Main Method:
    ```java
    int continueProgram;
    do {
    String input = JOptionPane.showInputDialog("Enter a DNA sequence").toUpperCase();
    String message = "Do you want to continue?";
    if (isValid(input))
    displayCodons(input);
    else
    message = "Invalid DNA Sequence.\n" + message;
    continueProgram = JOptionPane.showConfirmDialog(null, message, "Alert", JOptionPane.YESNOOPTION);
    } while (continueProgram == JOptionPane.YES_OPTION);
    JOptionPane.showMessageDialog(null, "Thanks for using the Codon Extractor!");

- **isValid Method**: Validates the DNA sequence.

java
public static boolean isValid(String dna) {
String validBases = "ACGT";
for (int i = 0; i < dna.length(); i++) {
char base = dna.charAt(i);
if (validBases.indexOf(base) == -1)
return false;
}
return true;
}

- **displayCodons Method**: Displays valid codons and handles remaining bases.

java
public static void displayCodons(String dna) {
String message = "";
for (int i = 0; i < dna.length() - 2; i += 3)
message += "\n" + dna.substring(i, i + 3);
int remaining = dna.length() % 3;
if (remaining == 1)
message += "\n" + dna.charAt(dna.length() - 1) + "*"; else if (remaining == 2) message += "\n" + dna.substring(dna.length() - 2, dna.length()) + "";
message = "dna length: " + dna.length() + "\n\nCodons: " + message;
JOptionPane.showMessageDialog(null, message, "Codons in DNA", JOptionPane.INFORMATION_MESSAGE);
}

### JFileChooser Class
- **Purpose**: Lets users choose files on their file system.  
- **Usage**:  
  - Create a new `JFileChooser` object and set the title with `fc.setDialogTitle(title)`.  
  - Call `fc.showOpenDialog(null)` to display the dialog.  
  - Check the return value (0 for open, 1 for cancel) and then get the selected file using `fc.getSelectedFile()`.

### FileChooser Example
- **Code Example**:

java
import java.io.File;
import javax.swing.JFileChooser;
public class FileChooser {
public static void main(String[] args) {
JFileChooser fc = new JFileChooser();
fc.setDialogTitle("Choose Important File");
int val = fc.showOpenDialog(null);
System.out.println(val);
File f = fc.getSelectedFile();
System.out.println(f);
}
}
```