Class relations mess - OOP

[Nicol Green]

Hi guys,
I am a bit of java newby and I need a assistance. The problem is:

I have 3 classes:

1. In class A there is instance of class B (Class A is the main class)
2. In class B there is instance of class C (class B implements GUI)
3. I need in class C some components from class B (in class C I have computations and set and get methods)

How should I do this in good programming manner ? I tried to make instance of class B in class C, but I get a StackOverFlow error, so suppose that is a wrong way. Actually I need in set method in class C to set value from TextField which is in class B. When I want to take that values, does that discomfit encapsulation ?

I hope it is not too confusing. Any help is welcome! Thanks!

[David Newton]

Without knowing more it sounds like one or more of your classes may be trying to do too much.

You're getting a stack overflow because the construction of one object creates an instance of another, which in turn creates an instance of the first, ad nauseum until the computer vomits.

There are a lot of solutions, which to use depends on your requirements. You could consider breaking up class responsibilities more granularly, just duplicating the fields you need, passing an instance of the one class into the other as a constructor parameter or setting it on the object after it's created, and so on.

[pete stein]

The simplest way is to have a B variable in C and then set the B variable either from a parameter passed into C's constructor or with a setB(B b) method. There are better ways, but this is a start.

For example:

public class A {
  public static void main(String[] args) {
    B b = new B();
  }
}

class B {
  C c;
  
  public B() {
    c = new C(this);
  }
}

class C {
  B b;
  
  public C(B b) {
    this.b = b;
  }
}

[Nicol Green]

Thank you very much for quick responses!

It is somehow possible to do at that way, but it is not working like it should, but still I am not sure is it good programming practice and encapsulation violation if I do that so to say two-way connection, like in previous post ?

[pete stein]

Nicol Green wrote:Thank you very much for quick responses!

It is somehow possible to do at that way, but it is not working like it should,

hm, a small program that compiles and runs and demonstrates the issue would probably go a long way toward helping us find out what's not working.

but still I am not sure is it good programming practice and encapsulation violation if I do that so to say two-way connection, like in previous post ?

I don't see it as an encapsulation violation, but more of an issue of tight coupling and poor cohesion. Better perhaps would be to use interfaces and appropriate Design Patterns to loosen coupling and increase cohesion.

[Nicol Green]

Ok! Here are the classes:

Class Operations:

public void setFirstNumber(double number){
       this.firstNumber = firstNumber;
}

public double getFirstNumber() {
      return firstNumber;
}
public void setSecondNumber(double number){
       this.secondNumber = secondNumber;
}

public double getSecondNumber() {
      return firstNumber;
}
public  void setOperatorEn(double operatorEn){
       this.operatorEn = operatorEn;
}
public double getOperatorEn(){
        return operatorEn;
}
public double doOperation(){
				
		switch(operatorEn){
		
			case Add: 
				
				result = firstNumber + secondNumber ;
				break;
					
			case Substruct:
				
				result = firstNumber - secondNumber;
				break;
                         default:
                                break; 
        }
}				

In class B:

JFormattedTextField textField = new JFormttedTextField();
String field = textField.getText();
JButton buttonAdd = new JButton();
JButton buttonEquals = new JButton();

buttonAdd.addActionListener(new ActionListener() {
				
				@Override
				public void actionPerformed(ActionEvent arg0) {
						
					if (!(textField.getText().equals("0."))) { 
						
						textField.setText("");
						
						operations.setFirstNumber(Double.valueOf(field));
												
						operations.setOperatorEn(Operators.Add);
							
					}					
				}
			});
buttonEquals.addActionListener(new ActionListener() {
				
				@Override
				public void actionPerformed(ActionEvent arg0) {
						
					if ((!(textField.getText().equals("0.")))) {
						
					operations.setSecondNumber(Double.valueOf(field));	
										
						operations.doOperation();						
						
					}
				}
			});

I wanted in doOperations(operatorEn)instead of result = firstNumber + secondNumber; to say
result = firstNumber + Double.valueOf(textField.getText());

[pete stein]

Your code appears to be missing some critical things, such as class signatures for one. Perhaps someone can help you based on this information, but likely not me. If you don't get help soon, as I recommended above, please post small compilable classes that demonstrate your problem, code that we can compile on our systems without having to modify them, without requiring outside dependencies (such as images on disks or database). If you do this, you'll make it much easier for others to help you and will likely increase the speed at which you'll get a useful answer.

Much luck!

[pete stein]

Nicol Green wrote:
...
I wanted in doOperations(operatorEn)instead of result = firstNumber + secondNumber; to say
result = firstNumber + Double.valueOf(textField.getText());

Ah, I can tell you this: that you really don't want to do this. doOperations is in your "model" while the textfield is in the "view" and in general, the model should have no dependencies on the view.

Again, if you post a simple app that does perhaps one operation, we can help you to better write this.

[pete stein]

For example, say my model, class MvcModel, is very simple -- only an add operation for illustrative purposes:

class MvcModel {
  public double addOperation(double input1, double input2) {
    return input1 + input2;
  }
}

But note that the model has no references to the GUI, meaning it's not tied to any one GUI and it can be used by a Swing GUI, an AWT GUI, an Android GUI or whatever. Also, I can fiddle around with my GUI code and know that by doing this, I'm not going to break my model code.

The GUI/view, class MvcView, will be simple, just 3 JTextFields and a JButton:

  private JTextField inputField1 = new JTextField(10);
  private JTextField inputField2 = new JTextField(10);
  private JTextField resultField = new JTextField(10);
  
  private JButton addButton = new JButton();

it will also let me set the control on my button via a public method: setAddControl:

  public void setAddControl(MvcAddControl control) {
    addButton.setAction(control);
  }

And also will have public methods to allow the control to extract the Strings from the two input fields, as well as a public method to allow the control to set the result field:

  public String getInputField1Text() {
    return inputField1.getText();
  }

  public String getInputField2Text() {
    return inputField2.getText();
  }
  
  public void setResultFieldText(String text) {
    resultField.setText(text);
  }

My control, MvcAddControl has a constructor that allows passage of a String, text, which is the button's text, an MvcView which is a reference the view object and an MvcModel param which is a reference to the model:

  public MvcAddControl(String text, MvcView view, MvcModel model) {
    super(text);
    this.view = view;
    this.model = model;
  }

Then in its action peformed method, it puts it all together, extracting the Strings from the view's jtextfields, converting them to doubles, adding them (using the model) and setting the results into the view's results field:

  public void actionPerformed(ActionEvent e) {
    view.setResultFieldText(""); // clear result field
    try {
      double input1 = Double.parseDouble(view.getInputField1Text());
      double input2 = Double.parseDouble(view.getInputField2Text());
      double result = model.addOperation(input1, input2); // use the model here
      view.setResultFieldText(String.valueOf(result));
    } catch (NumberFormatException nfe) {
      JOptionPane.showMessageDialog(view.getComponent(), "Only Numbers Can be Entered",
              "Incorrect Data Entered", JOptionPane.ERROR_MESSAGE);
    }
  }

I then have a main class, MvcMain creates a model, control and view object, ties them all together and then display's the view's main JPanel in a JFrame:

public class MvcMain {
  private static void createAndShowUI() {
    MvcModel model = new MvcModel();
    MvcView view = new MvcView();
    MvcAddControl addControl = new MvcAddControl("Add", view, model);
    view.setAddControl(addControl);
    
    JFrame frame = new JFrame("Mini Calc");
    frame.getContentPane().add(view.getMainPanel());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        createAndShowUI();
      }
    });
  }
}

Putting it all together, we have:

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

public class MvcMain {
  private static void createAndShowUI() {
    MvcModel model = new MvcModel();
    MvcView view = new MvcView();
    MvcAddControl addControl = new MvcAddControl("Add", view, model);
    view.setAddControl(addControl);
    
    JFrame frame = new JFrame("Mini Calc");
    frame.getContentPane().add(view.getMainPanel());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        createAndShowUI();
      }
    });
  }
}

class MvcView {
  // mainPanel holds all the GUI components
  private JPanel mainPanel = new JPanel();
  
  // two input fields and the result textfield
  private JTextField inputField1 = new JTextField(10);
  private JTextField inputField2 = new JTextField(10);
  private JTextField resultField = new JTextField(10);
  
  private JButton addButton = new JButton();

  public MvcView() {
    resultField.setEditable(false);
    
    mainPanel.add(inputField1);
    mainPanel.add(inputField2);
    mainPanel.add(new JLabel("="));
    mainPanel.add(resultField);
    mainPanel.add(addButton);
  }
  
  public void setAddControl(MvcAddControl control) {
    addButton.setAction(control);
  }

  public JPanel getMainPanel() {
    return mainPanel;
  }
  
  public String getInputField1Text() {
    return inputField1.getText();
  }

  public String getInputField2Text() {
    return inputField2.getText();
  }
  
  public void setResultFieldText(String text) {
    resultField.setText(text);
  }

}

class MvcAddControl extends AbstractAction {
  private MvcModel model;
  private MvcView view;
  
  public MvcAddControl(String text, MvcView view, MvcModel model) {
    super(text);
    this.view = view;
    this.model = model;
  }
  
  public void actionPerformed(ActionEvent e) {
    view.setResultFieldText(""); // clear result field
    try {
      double input1 = Double.parseDouble(view.getInputField1Text());
      double input2 = Double.parseDouble(view.getInputField2Text());
      double result = model.addOperation(input1, input2); // use the model here
      view.setResultFieldText(String.valueOf(result));
    } catch (NumberFormatException nfe) {
      JOptionPane.showMessageDialog(view.getMainPanel(), "Only Numbers Can be Entered",
              "Incorrect Data Entered", JOptionPane.ERROR_MESSAGE);
    }
  }
}

class MvcModel {
  public double addOperation(double input1, double input2) {
    return input1 + input2;
  }
}

[Nicol Green]

Pete, thank you very much!

Your posts were from great help!
I was just read it, because at the moment I am working at something else, but soon I will adjust it to my code, and let you know how it is working. I am really sorry, I was typing fast so some main parts unfortunately are missing in my last post.. I will be more careful.

I just have one more, maybe stupid question. Since I am a beginner..
Is there any rule, when I need some values for example, when I need to use method with return values, and when I need method with passing parameters ? Return values I use when I need some value from another method somewhere else, but with passing parameters I am getting stuck.

[Campbell Ritchie]

Depends on the method. If your method needs information sent to it, the receiving method calls that its parameters (and the sending method calls that arguments).

If you look through the javadoc for a class (let's try String which was the first one to come to hand), click METHOD, and look at the return types in the left column, which tell you what each method returns. Notice you only ever return one thing (or nothing, in which case it says void, but String hasn't got many void methods).
Notice that where it gives the method heading, there are things in the (). Each of those represents a parameter, so you have to provide arguments of the same type and number when you call those methods. Note some of them specify a range; try passing -1 to a method taking an int parameter and see what happens.

When you write your methods, you will put the parameter types and what you are calling themfor this method in the () after the method name. And you put the return type (or void) to the left of the method name. You have to decide what pieces of information your method needs, and that is how many parameters you write.

[Campbell Ritchie]

And about return types, you might find this thread about "void" useful. Or maybe not.

[Nicol Green]

The text about void was useful, thanks!

I understand concept of class relations in Your example. But now I have a bit different situation, but it is somehow the same question.

I have class with GUI implemented and there I have a 3 text area (for plainText, for keyword and for cipherText)encryption button. I would like to implement Playfair and Vigenere cipher on on click event. But Playfair and Vigenere are separated classes, with a few methods. How do I do that connection between them ? Classes follows:

public class CipherTextGeneratorView extends JFrame 
private JLabel labelPlainText = new JLabel("Message:");
	private JTextArea plainTextArea = new JTextArea();
	private JLabel labelKey = new JLabel(Keyword: ");
	private JTextArea keyTextArea = new JTextArea();
	private JLabel labelChipher = new JLabel("Cipher:");
	private JTextArea chipherTextArea = new JTextArea();
	private JComboBox chipher = new JComboBox();
	private JLabel labelChipherAlgorithm = new JLabel("Cipher algorithm:");

public void setGUIComponents(){		
			
		setWindow();
		setMenu();	
		
		setGroupBoxEncryption();
			
	}
	
	public void setWindow() {
		
		this.setDefaultCloseOperation(EXIT_ON_CLOSE);		
		setBounds(130, 30, 760, 700);
		setVisible(true);
		setResizable(false);
		setLayout(null);
		setTitle("Generator");
		
	}

// Sets GUI components in group box Encryption
	public void setGroupBoxEncryption(){
				
		// Creates groupBox 
		add(groupBoxEncryption);
		groupBoxEncryption.setLayout(null);
		groupBoxEncryption.setVisible(true);
		groupBoxEncryption.setBounds(30, 40, 700, 290);
		groupBoxEncryption.setBorder(BorderFactory.createTitledBorder(null, "Šifrovanje", TitledBorder.DEFAULT_JUSTIFICATION, TitledBorder.DEFAULT_POSITION, new Font("Dialog", Font.BOLD, 12), new Color(51, 51, 51)));
		
		// Add TextArea plainText to the Panel
		groupBoxEncryption.add(plainTextArea);
		plainTextArea.setBounds(100, 30, 250, 100);
		plainTextArea.setVisible(true);
		plainTextArea.setBorder(BorderFactory.createLineBorder(Color.gray));
		plainTextArea.setLineWrap(true);
	
		// Set maximum characters number for the textArea line
		RowLength rowLengthPlainText = new RowLength(plainTextArea, 31);
		plainTextArea.setDocument(rowLengthPlainText);
		
		// Add TextArea keyText to the Panel
		groupBoxEncryption.add(keyTextArea);
		keyTextArea.setBounds(100, 150, 250, 50 );
		keyTextArea.setVisible(true);
		keyTextArea.setBorder(BorderFactory.createLineBorder(Color.gray));
	
		// Set maximum characters number for the textArea line
		RowLength rowLengthKeyText = new RowLength(plainTextArea, 31);
		plainTextArea.setDocument(rowLengthKeyText);
		
		// Add TextArea chipherText to the Panel
		groupBoxEncryption.add(chipherTextArea);
		chipherTextArea.setBounds(430, 30, 250, 100);
		chipherTextArea.setVisible(true);
		chipherTextArea.setBorder(BorderFactory.createLineBorder(Color.gray));
	
		// Set maximum characters number for the textArea line
		RowLength rowLengthChipherText = new RowLength(plainTextArea, 31);
		plainTextArea.setDocument(rowLengthChipherText);
		
		groupBoxEncryption.add(labelPlainText);
		labelPlainText.setVisible(true);
		labelPlainText.setLabelFor(plainTextArea);		
		labelPlainText.setBounds(new Rectangle(50, 30, 38, 16));
		
		groupBoxEncryption.add(labelKey);
		labelKey.setVisible(true);
		labelKey.setLabelFor(keyTextArea);
		labelKey.setBounds(new Rectangle(50, 150, 78, 16));
		
		groupBoxEncryption.add(labelChipher);
		labelChipher.setVisible(true);
		labelChipher.setLabelFor(chipherTextArea);
		labelChipher.setBounds(380, 30, 38, 16);
		
		groupBoxEncryption.add(chipherListCombo);		
		chipherListCombo.setBounds(100, 220, 250, 21);
		chipherListCombo.setVisible(true);
		chipherListCombo.addItem("Izaberite algoritam šifrovanja..");
		
		chipherList[0] = "Vegenere";
		chipherListCombo.addItem(chipherList[0]);
		
		chipherListCombo.addItem("Playfair");

 chipherListCombo.addItemListener(new ItemListener(){
		      public void itemStateChanged(ItemEvent ie){
		        String str = (String)chipherListCombo.getSelectedItem();
		        if (str == "Vegenere"){
		        	
		        	// here put code for Vigenere 
		        	
		        }
		      
		      }
		    });

JButton buttonEncryption = new JButton("Encryption");
			groupBoxEncryption.add(buttonEncryption);
			buttonEncryption.setVisible(true);
			buttonEncryption.setBounds(100, 250, 90, 24);
			buttonEncryption.setFont(new Font("Arial", Font.PLAIN, 12));
			
			buttonEncryption.addActionListener(new ActionListener(){
				public void actionPerformed(ActionEvent e){
					String str = (String)chipherListCombo.getSelectedItem();
			        if (str == "Playfair"){
}
}

package chipherTextGenerator;

/**
 * Implementation for PLAYFAIR encryption algorithm.
 * @author Tolnai Andrei Ciprian
 */
public class Playfair extends Encryption {

        private int matrix[] = new int[25];
        private int letterPosition[] = new int[26];

        @SuppressWarnings("unused")
        private String key;

      
        Playfair() {
                // constructor hidden
        }

        public Playfair(String key) {
                this.name = Playfair.class.getSimpleName();
                char c;
                int n = 0, i = 0;
                String keyABC = key.toUpperCase().replaceAll("J", "I");
                this.key = key;
                for (c = 'A'; c <= 'Z'; c++) {
                        setPosFree(c);
                        keyABC += ((c == 'J') ? "" : "" + c);
                }

                while (n < keyABC.length()) {
                        c = keyABC.charAt(n++);
                        if (isLetter(c) && isPosFree(c)) {
                                setChar(i, c);
                                setPos(c, i);
                                i++;
                        }
                }
                setPos('J', getPos('I'));
        }

        public char getChar(int index) {
                return (char) (matrix[index] + 'A');
        }

        private int getPos(char c) {
                return letterPosition[c - 'A'];
        }

        private void setChar(int index, char c) {
                matrix[index] = c - 'A';
        }

        private void setPos(char c, int index) {
                letterPosition[c - 'A'] = index;
        }

        private void setPosFree(char c) {
                setPos(c, -1);
        }

        private boolean isPosFree(char c) {
                return (getPos(c) == -1);
        }

        private boolean isLetter(char c) {
                return (('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z'));
        }

        private String swap(int pos1, int pos2, int d) {
                int x1 = pos1 % 5;
                int y1 = pos1 / 5;
                int x2 = pos2 % 5;
                int y2 = pos2 / 5;

                if (x1 != x2 && y1 == y2) {
                        x1 = (x1 + d) % 5;
                        x2 = (x2 + d) % 5;
                }
                if (x1 == x2 && y1 != y2) {
                        y1 = (y1 + d) % 5;
                        y2 = (y2 + d) % 5;
                }
                if (x1 != x2 && y1 != y2) {
                        int x = x1;
                        x1 = x2;
                        x2 = x;
                }

                return getChar(x1 + y1 * 5) + "" + getChar(x2 + y2 * 5);
        }

        private String _encrypt(String text, int direction) {
                String toReturn = "";
                int i = 0;
                while (i < text.length()) {
                        toReturn += swap(getPos(text.charAt(i++)), getPos(text.charAt(i++)), direction + 5);
                }
                return toReturn;
        }

      
        public String encrypt(String text) {
                return _encrypt(replacedText(text).toUpperCase(), 1);
        }

        public String decrypt(String text) {
                return _encrypt(cryptText(text), -1).toUpperCase();
        }

        public String replacedText(String text) {
                char c;
                int n = 0;
                int p;
                String t = "";
                text = text.toLowerCase();
                while (n < text.length()) {
                        c = text.charAt(n++);
                        if (c == 'j') {
                                c = 'i';
                        }
                        if (isLetter(c)) {
                                p = t.length() - 1;
                                t += (p >= 0 && c == t.charAt(p) && p % 2 == 0) ? "x" + c : "" + c;
                        }
                }
                return (t.length() % 2 == 0) ? t : t + "x";
        }

        private String cryptText(String text) {
                char c;
                int n = 0;
                String t = "";
                text = text.toUpperCase();
                while (n < text.length()) {
                        c = text.charAt(n++);
                        t += (isLetter(c)) ? c + "" : "";
                }
                return (t.length() % 2 == 0) ? t : t + "X";
        }

        public String showMatrix() {
                String t = "Matrix: \n";
                for (int n = 0; n < 25; n++)
                        t += getChar(n) + ((n % 5 == 4) ? "\n" : " ");
                return t;
        }

        public String showMatrixPosition() {
                String t = "Positions in matrix: \n";
                for (char c = 'A'; c <= 'Z'; c++)
                        t += c + ": " + getPos(c) + (((c - 'A') % 7 == 6) ? "\n" : "\t");
                return t + "\n";
        }

        public String showWithSpaces(String text) {
                String toReturn = "";
                for (int n = 0; n < text.length(); n++)
                        toReturn += text.charAt(n) + ((n % 2 == 1) ? " " : "") + ((n % 60 == 59) ? "\n" : "");
                return toReturn + "\n";
        }

        public void setKey(String key) {
                this.key = key;
        }

       
        protected void setKey(byte[] key) {
                // not used
        }
}




public abstract class Encryption2 extends Utils {

    protected String name;

    /**
     * How big a block is
     */
    protected int blockSize;

    /**
     * How big a key is. Key-less ciphers use 0. Variable-length-key ciphers
     * also use 0.
     */
    protected int keySize;

    /**
     * Encryption method.
     *
     * @param text
     * @return
     */
    public abstract String encrypt(String text);

    /**
     * Decryption method.
     *
     * @param text
     * @return
     */
    public abstract String decrypt(String text);

    /**
     * Utility routine to turn a string into a key of the right length.
     *
     * @param keyStr
     * @return
     */
    protected byte[] makeKey(String keyStr) {
            byte[] key;
            if (keySize == 0) {
                    key = new byte[keyStr.length()];
            } else {
                    key = new byte[keySize];
            }
            int i, j;

            for (j = 0; j < key.length; ++j) {
                    key[j] = 0;
            }

            for (i = 0, j = 0; i < keyStr.length(); ++i, j = (j + 1) % key.length) {
                    key[j] ^= (byte) keyStr.charAt(i);
            }

            return key;
    }

    /**
     * Set the key.
     *
     * @param key
     */
    protected abstract void setKey(byte[] key);

    /**
     * Utility routine to set the key from a string.
     *
     * @param keyStr
     */
    protected void setKey(String keyStr) {
            setKey(makeKey(keyStr));
    }

    public String getName() {
            return name;
    }
}

Any help will be appreciated, and Thank You in advance!

[David Newton]

I think you should continue this in your other thread rather than resurrecting this old one.

[Campbell Ritchie]

David Newton wrote:I think you should continue this in your other thread rather than resurrecting this old one.

In that case I shall close this thread.