Java Factorial GUI

Question

The goal is to create a program which utilizes a GUI to calculate a factorial. I need to create a jPanel or jFrame to display the results of the program. Then I need to get the text from JTextField and parse it to an Integer so it can be passed to a constructor. Thirdly, an object class needs to be created with an instance variable of type int called factorial. This object class needs a single argument constructor named Factorial that accepts an int and assigns the value to the instance variable. Then it should have a method that calculates the factorial using a for loop with a return type of int. Finally, it should display the value of the object after calling the method that computes the factorial. Here is my work so far.

import javax.swing.JFrame;

public class factorialCalc

{

     public static void main (String[] args)

     {

          JFrame frame=new JFrame ("Factorial Calculator");

          frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

          Factorial panel=new Factorial();

          frame.getContentPane().add(panel);

          frame.pack();

          frame.setVisible(true);

     }

}

And my next file is the Object class:

 import java.awt.*;

 import java.awt.event.*;

 import javax.swing.*;



 public class Factorial extends JPanel

 {

          private int factorial; 

          private JLabel inputLabel,resultLabel;

          private JTextField factorialText;

          private JButton factButton;



           //Constructor: sets up main GUI components

           public void FactorialPanel(int factorial)

           {

                this.factorial=factorial;

                inputLabel= new JLabel ("Please enter an integer:");

                factButton = new JButton("Compute");

                TempListener listener=new TempListener();

                factButton.addActionListener(listener);

                factorialText = new JTextField();

                factorialText.addActionListener (new TempListener());

                add(inputLabel);

                add(factorialText);

                add(resultLabel);

           }

           //represents a listener for the button

           private class TempListener implements ActionListener

           {

            //performs factorial operation when the 'Compute' button is  pressed

            public int computeFactorial(ActionEvent event)

            {

                 int text=Integer.parseInt(factorial);

                 int f =1;

                 for(int i=text;i>=1;i--)

                 {      

                      f = f*i;

                 }  

                  resultLabel.setText(Integer.toString(f));

            }

       }

 }

These are the following errors I get when I try to compile:

.\Factorial.java:31: error: Factorial.TempListener is not abstract and does not override abstract method actionPerformed(ActionEvent) in ActionListener
    private class TempListener implements ActionListener
            ^
  .\Factorial.java:37: error: incompatible types: int cannot be converted to String
                    int text=Integer.parseInt(factorial);
                                              ^
  Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
  2 errors

Why does it not let me parse the String factorial into and integer?

Also, how and where can I call the computeFactorial method to display the value of the object?

Thank you! Any help is appreciated!

Answer 1

Instead of using factorial here, which is already an int (hence the error)...

int text=Integer.parseInt(factorial);

... I think you meant to get the JTextField value:

int text=Integer.parseInt(factorialText.getText());

Also, if TempListener implements ActionListener , then you must follow the ActionListener interface. The method is called actionPerformed() ...

 public int actionPerformed(ActionEvent event)

You can't just rename it to whatever you want, like you did here:

public int computeFactorial(ActionEvent event)

Finally, based on your comment, another issue is you misnamed your constructor. If your class is defined as:

public class Factorial extends JPanel

Then your constructor might be:

public Factorial(int factorial)  // note: no void and same name as class

Answer 2

Listen to your compiler:

error: Factorial.TempListener is not abstract and does not override abstract method actionPerformed(ActionEvent) in ActionListener

It's easy for a beginner to think "Oh, that's a load of babble, I'll try stuff instead of trying to understand what it says" -- but you need to understand them because they tell you exactly what the compiler is complaining about.

Here's it's telling you that because Factorial.TempListener implements ActionListener , it expects it to have a method actionPerformed(ActionEvent) .

If ActionListener was abstract , it would be allowed to not have this method -- but then you wouldn't be able to instantiate it, so just adding abstract won't help.

So you need to write actionPerformed(ActionListener) .

What that method should do is beyond what SO is for -- read and understand a book or tutorial on Swing.

No doubt once you fix this there will be more compiler errors. Read them; they usually tell you where the problem is.