Getting preview of final text from jTextField

Question

I’m trying to create JTextField that can accept only double (including scientific notation) with this check:

abstract class DoubleKeyAdapter extends KeyAdapter
{
    @Override
    public void KeyTyped(KeyEvent e)
    {
        if (!(((JTextField) e.getSource()).getText() + e.getKeyChar()).matches(“[+-]?\\d*(\\.\\d*)?([eE][+-]?\\d*)?”))
            e.consume();
    }

    @Override
    public abstract void KeyReleased(KeyEvent e);
}

The problem is when I try to add - for example to the beggining of the text field. it doesn’t let me do so because it does the checking by appending - at the end of the text, in other words, I can’t know where the new character had been added. So my questions are:

1. Is there a way to get a preview of the entire text before it is present in the text field?
2. Is there a way to create JTextField (or extention of it) that does it better?
3. Is there a way to know the location of the new character?

Answer 1

You can use a DocumentFilter for this.

It allows you to do editing before the text is inserted into the Document.

import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;

public class DoubleFilter extends DocumentFilter
{
    @Override
    public void insertString(FilterBypass fb, int offset, String text, AttributeSet attributes)
        throws BadLocationException
    {
        replace(fb, offset, 0, text, attributes);
    }

    @Override
    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attributes)
        throws BadLocationException
    {
        //  In case someone tries to clear the Document by using setText(null)

        if (text == null)
            text = "";

        //  Build the text string assuming the replace of the text is successfull

        Document doc = fb.getDocument();
        StringBuilder sb = new StringBuilder();
        sb.append(doc.getText(0, doc.getLength()));
        sb.replace(offset, offset + length, text);

        if (validReplace(sb.toString()))
            super.replace(fb, offset, length, text, attributes);
        else
            Toolkit.getDefaultToolkit().beep();
    }

    private boolean validReplace(String text)
    {
        //  In case setText("") is used to clear the Document

        if (text.isEmpty())
            return true;

        //  Verify input is a Double

        try
        {
            Double.parseDouble( text );
            return true;
        }
        catch (NumberFormatException e)
        {
            return false;
        }
    }

    private static void createAndShowGUI()
    {
        JTextField textField = new JTextField(10);
        AbstractDocument doc = (AbstractDocument) textField.getDocument();
        doc.setDocumentFilter( new DoubleFilter() );
        textField.setText("123");
        textField.setText("123567");
        textField.setText(null);

        JFrame frame = new JFrame("Integer Filter");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout( new java.awt.GridBagLayout() );
        frame.add( textField );
        frame.setSize(220, 200);
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args) throws Exception
    {
        EventQueue.invokeLater( () -> createAndShowGUI() );
/*
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
*/
    }

}

It doesn't do everything you want, but it should get you started.

Answer 2

My take on the solution, inspired by @camickr, and added 2 methods: getDouble() and setDouble()

import javax.swing.*;
import javax.swing.text.*;
import java.util.regex.Pattern;

public class JDoubleField extends JTextField
{
    private static final DocumentFilter doubleFilter = new DocumentFilter()
    {
        private final Pattern pattern = Pattern.compile("[+-]?(NaN|Infinity|\\d*(\\.\\d*)?((?<=\\d\\.?)[eE][+-]?\\d*)?)");

        @Override
        public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException
        {
            replace(fb, offset, 0, string, attr);
        }

        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException
        {
            if (text == null || pattern.matcher(new StringBuilder(fb.getDocument().getText(0, fb.getDocument().getLength()))
                    .replace(offset, offset + length, text))
                    .matches())
                super.replace(fb, offset, length, text, attrs);
        }
    };

    public double getDouble()
    {
        try
        {
            return Double.parseDouble(getText());
        } catch (NumberFormatException ignored)
        {
            return Double.NaN;
        }
    }

    public void setDouble(double num)
    {
        setText(String.valueOf(num));
    }

    public JDoubleField()
    {
        this(0);
    }

    public JDoubleField(double num)
    {
        this(String.valueOf(num));
    }

    public JDoubleField(double num, int columns)
    {
        this(String.valueOf(num), columns);
    }

    public JDoubleField(Document doc, double num, int columns)
    {
        this(doc, String.valueOf(num), columns);
    }

    public JDoubleField(int columns)
    {
        this(null, columns);
    }

    public JDoubleField(String text)
    {
        this(text, 0);
    }

    public JDoubleField(String text, int columns)
    {
        this(null, text, columns);
    }

    public JDoubleField(Document doc, String text, int columns)
    {
        super(doc, null, columns);
        ((AbstractDocument) getDocument()).setDocumentFilter(doubleFilter);
        if (text != null)
            setText(text);
    }
}