Changing textfield to show only uppercase&lowercase

Question

I want the first letter in a textfield to be uppercase, and when user press "SPACE" first letter to be again uppercase. I'm really sorry for asking lots of questions, but it's my first month in programming and also in java.

My function for textfield:

private void userNameTextFieldPressed(final java.awt.event.KeyEvent event) {
int key = event.getKeyChar();
if (Character.isAlphabetic(event.getKeyChar())) {
        || (key >= event.VK_A && key <= event.VK_Z)
        || key == event.VK_BACK_SPACE) {
    this.userNameTextField.setEditable(true);
    this.userNameTextField.setBackground(Color.GREEN);
} else {
    this.userNameTextField.setEditable(false);
    this.userNameTextField.setBackground(Color.RED);
 }
}    
}

@MadProgrammer and how can i make it work when user press "SPACE" to change again to uppercase? — A. Omag, Feb 02 '19 at 00:03
You inspect the incoming text and and the existing text and make decisions about how best to filter it, that's kind of the point — MadProgrammer, Feb 02 '19 at 00:05

MadProgrammer · Answer 1 · 2019-02-02T00:22:59.303

Don't

Use a KeyLisyener on text components, it's not an appropriate mechanism for a number of reasons

Do

Use a DocumentFilter to change the text before it's applied to the physical Document

See Implementing a Document Filter for more details

As a (very quick and basic) example...

public class PropercaseDocumentFilter extends DocumentFilter {

    @Override
    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
        text = modify(fb, offset, text, attrs);
        super.replace(fb, offset, length, text, attrs);
    }

    protected String modify(FilterBypass fb, int offset, String text, AttributeSet attrs) throws BadLocationException {
        if (text.length() > 0) {
            Document doc = fb.getDocument();
            StringBuilder sb = new StringBuilder(text);
            if (doc.getLength() == 0) {
                sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
            } else if (offset > 0 && offset < doc.getLength()) {
                if (doc.getText(offset - 1, 1).equals(" ")) {
                    sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
                }
            } else if (doc.getText(doc.getLength() - 1, 1).equals(" ")) {
                sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
            }
            text = sb.toString();
        }
        return text;
    }

}

What this example doesn't do, is change text that is pasted (apart from the first character), you'll need to think about how you want that dealt with and make the appropriate changes

And because I know no one reads the documentation or tutorials...

import java.awt.EventQueue;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;

public class JavaApplication100 {

    public static void main(String[] args) {
        new JavaApplication100();
    }

    public JavaApplication100() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            setBorder(new EmptyBorder(10, 10, 10, 10));
            JTextField field = new JTextField(10);
            ((AbstractDocument)field.getDocument()).setDocumentFilter(new PropercaseDocumentFilter());
            add(field);
        }

    }

    public class PropercaseDocumentFilter extends DocumentFilter {

        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
            text = modify(fb, offset, text, attrs);
            super.replace(fb, offset, length, text, attrs);
        }

        protected String modify(FilterBypass fb, int offset, String text, AttributeSet attrs) throws BadLocationException {
            if (text.length() > 0) {
                Document doc = fb.getDocument();
                StringBuilder sb = new StringBuilder(text);
                if (doc.getLength() == 0) {
                    sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
                } else if (offset > 0 && offset < doc.getLength()) {
                    if (doc.getText(offset - 1, 1).equals(" ")) {
                        sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
                    }
                } else if (doc.getText(doc.getLength() - 1, 1).equals(" ")) {
                    sb.setCharAt(0, Character.toUpperCase(sb.charAt(0)));
                }
                text = sb.toString();
            }
            return text;
        }

    }

}

Changing textfield to show only uppercase&lowercase

1 Answers1

Don't

Do