Lab 12:
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Download the support code for the Sudoku assignment. Try to understand first the Sudoku class and the JUnit test classes. Then look over the Row and PartialSolution classes to understand how a game board is represented as Java objects.
Exercises
1. Look at the implementation of the toString() function of the PartialSolution class. This implementation has problems of performance and functionality (does not work correctly in all cases). What are these problems? Write a new implementation for the toString() function that avoids both problems.
2. Write a function that tests if a PartialSolution is a descendent of another PartialSolution (a descendent is "included" in its parent). Write Junit tests for this function.
Graphical User Interfaces (GUI's) in Java
For most of the relevant Information on how to build GUIs in Java, see the following reference: Java GUI Programming Primer
The content below discusses material not explicitly covered in the above reference.
Few people code GUI's by hand these days--it's just too complicated. Typically, one would use a "GUI builder" to drag-and-drop GUI components onto a design canvas, greatly simplifying and speeding up the GUI creation process. But it is very helpful to know the basics of how to build a GUI by hand because one often needs to go in an manually tweak the GUI code even when using a sophisticated GUI builder tool.
Basic structure of a simple GUI application:
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import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class MyGUIApp extends JFrame {
// Use fields for GUI components that need to be referenced outside of the GUI initialization process (initGUI)
/**
* Constructor for the GUI.
*/
public MyGUIApp() {
// initialize fields here. Surrounding your code in a protective try-catch is recommended.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Causes the application to end if the GUI frame is closed.
initGUI(); // initialize the GUI components
}
/**
* Actually start the GUI
*/
public void start() {
// Do any last second initializations, if needed.
setVisible(true); // Make the GUI visible
}
/**
* Initialize the GUI components
*/
private void initGUI() {
Container contentPane = getContentPane(); // all GUI components are added to the frame's ContentPane.
// You can also just call the accessor each time as well and not use a local variable.
// instantiate, initialize and connect all the GUI's components here.
// Don't forget to add them to the container that holds them, e.g. the ContentPane.
}
/**
* Main method that starts the app.
* In general, this would not be in this class but rather in a separate "controller" class
* with slightly different coding (as required for a true Model-View-Controller system).
* We put it here for now, for simplicity's sake only.
*/
public static void main(String[] args) {
// initialize and start the GUI on the GUI thread.
SwingUtilities.invokeLater(new Runnable() {
public void run() {
MyGUIApp view = new MyGUIApp(); // instantiate the GUI but don't show it yet.
// Model classes would be instantiated here plus any other required objects.
view.start(); // Start the application by making the GUI visible.
}
});
}
}
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Some typical GUI initializations:
Set title and size of the frame:
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setTitle("My Incredible GUI App"); // set the frame's title
setSize(400, 300); // set frame size to 400x300
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Panels in main frame:
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JPanel controlPnl = new JPanel();
controlPnl.setBackground(Color.BLUE); // Set panel color to blue
contentPane.add(controlPnl, BorderLayout.NORTH); // Fixed-size panel for control components, e.g. buttons, textfields, etc, at the top of the frame.
JPanel displayPnl = new JPanel();
contentPane.add(displayPnl, BorderLayout.CENTER); // Adjustable-size panel for display components, e.g. text areas, etc, in the middle of the frame.
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A Button with a listener on the control panel:
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JButton runBtn = new JButton("Run!");
runBtn.addActionListener(new ActionListener() {
/**
* This method runs when the button is clicked.
*/
public void actionPerformed(ActionEvent evt) {
// Do stuff here. Generally, delegate to a non-GUI object (the "model").
}
});
controlPnl.add(runBtn);
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A Label and a TextField with a listener on the control panel:
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JLabel infoLbl = new JLabel();
infoLbl.setText("Enter text here:");
controlPnl.add(infoLbl);
final JTextField infoTF = new JTextField("default text"); // don't need "final" below if this line was defining a field instead of a local variable.
infoTF.setPreferredSize(new java.awt.Dimension(75, 23)); // set default text field size to 75x23 pixels.
infoTF.addActionListener(new ActionListener() {
/**
* This method runs when "Enter" is pressed after entering text into the text field.
*/
public void actionPerformed(ActionEvent evt) {
String text = infoTF.getText(); // the text of the text field.
// Do stuff here. Generally, delegate to a non-GUI object (the "model").
}
});
controlPnl.add(infoTF);
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A text area with scroll bars in the center of the frame:
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JScrollPane scrollPn = new JScrollPane();
contentPane.add(scrollPn, BorderLayout.CENTER); // No center panel needed. ScrollPane added directly to frame.
JTextArea displayTA = new JTextArea("initial text");
scrollPn.setViewportView(displayTA); // put the text area in the scroll pane
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SerialVersionUID compiler warning:
A very common compiler warning to receive is the following for your frame class and other customized GUI components:
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The serializable class XXX does not declare a static final serialVersionUID field of type long |
If you do, add the following field to the class:
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private static final long serialVersionUID = 42L; // Use a random, unique integer value here |
For more information, see this web page 3. The tests for the support functions in the class PartialSolution are too few. Many situations are not properly tested. Extend what is already offered with tests as varied as you can. (What you write here can be submitted as partial solution for the Sudoku assignment) .