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I am working on a java swing project that looks like a Terminal (but with less functionality).

The GUI contains a jTextArea to display output and a jTextField for user input.

Here is an application of the my GUI to perform a simple task.

  1. Ask the user to enter a number.
  2. If successful, ask the user to enter a smaller
  3. If successful, prompt out the text "done!".

Is there a better way to do this other than state machine?

Here is the code:

package com.TerminalPanelGUI;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class TerminalPanel extends javax.swing.JPanel
{
    private int state;

    /**
     * Creates a new Terminal Panel
     */
    public TerminalPanel()
    {
        state = 0;
        initComponents();

        textArea.setText("Enter a number: \n");

        textField.addActionListener(new ActionListener()
        {
            @Override
            public void actionPerformed(ActionEvent ae)
            {
                System.out.println("In action performed: state is " + state);
                switch(state)
                {
                    case 0:
                        State0();
                        break;
                    case 1:
                        State1();
                        break;
                }
            }
        });
    }

    private int dummy;

    private void State0()
    {
        try
        {
            dummy = Integer.parseInt(textField.getText());
            state = 1;

            //prompt for next state
            textArea.append("Enter a smaller number: \n");
        }
        catch(NumberFormatException e)
        {
            textArea.append("Invalid entry. Try again \n");
            state = 0;
        }
    }

    private void State1()
    {
        try
        {

            if(Integer.parseInt(textField.getText()) < dummy)
            {
                state = 2;

                //prompt for next state
                textArea.append("done!");
            }
            else
            {
                state = 1;

                //prompt for next state
                textArea.append("Enter a smaller number: \n");
            }
        }
        catch(NumberFormatException e)
        {
            textArea.append("Invalid entry. Try again \n");
        }
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        scrollPane = new javax.swing.JScrollPane();
        textArea = new javax.swing.JTextArea();
        textField = new javax.swing.JTextField();

        setLayout(new org.netbeans.lib.awtextra.AbsoluteLayout());

        textArea.setEditable(false);
        textArea.setColumns(20);
        textArea.setRows(5);
        scrollPane.setViewportView(textArea);

        add(scrollPane, new org.netbeans.lib.awtextra.AbsoluteConstraints(0, 0, 400, 250));
        add(textField, new org.netbeans.lib.awtextra.AbsoluteConstraints(0, 270, 400, 30));
    }// </editor-fold>                        

    // Variables declaration - do not modify                     
    private javax.swing.JScrollPane scrollPane;
    protected javax.swing.JTextArea textArea;
    protected javax.swing.JTextField textField;
    // End of variables declaration                   
}
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Maybe something like this? Note: may add textField as a member of State0 and State1

public interface State
{
    boolean hasNext();
    State next();
}

public final class State0
    implements State
{
    private boolean okToContinue = false;
    private int number;

    @Override
    public boolean hasNext()
    {
        try {
            textArea.append("Enter a number");
            number = Integer.parseInt(textField.getText());
            okToContinue = true;
        } catch (NumberFormatException ignored) {
            textArea.append("Input is not a number");
        }
        return true;
    }

    @Override
    public State next()
    {
        return okToContinue ? new State1(number) : this;
    }
}

The State1 implementation is then obvious. In the main loop you can just do:

State state = new State0();

while (state.hasNext())
    state = state.next();
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