📝 JTextField in Java Swing

1️⃣ Introduction to JTextField

A JTextField is a GUI component in Java Swing used to accept single-line text input from the user.

Why Use JTextField?

✔️ Allows user input
✔️ Supports text editing, selection, and copying
✔️ Can be customized with font, size, color, and events

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2️⃣ Creating a Basic JTextField

Example: Adding a Text Field to a JFrame

import javax.swing.*;

public class JTextFieldExample {
    public static void main(String[] args) {
        // Create JFrame
        JFrame frame = new JFrame("JTextField Example");
        frame.setSize(300, 150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        // Create JTextField
        JTextField textField = new JTextField("Enter text here...", 20);
        
        // Add text field to frame
        frame.add(textField);

        // Make frame visible
        frame.setVisible(true);
    }
}

Explanation

✔️ new JTextField("Enter text here...", 20); → Creates a text field with placeholder text and a 20-character width.
✔️ frame.add(textField); → Adds the text field to the frame.
✔️ By default, text is left-aligned inside the field.

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3️⃣ Getting and Setting Text

Example: Read & Change Text in JTextField

String inputText = textField.getText();  // Get user input
textField.setText("New text");  // Set new text

✔️ getText() → Returns the current text in the field.
✔️ setText("New text") → Updates the field content.

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4️⃣ Handling JTextField Events with ActionListener

When the Enter key is pressed inside a JTextField, an ActionEvent occurs.

Example: Detecting User Input

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

public class JTextFieldEventExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("JTextField Event");
        frame.setSize(300, 150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JTextField textField = new JTextField(20);
        JLabel label = new JLabel("Enter your name:");

        // Add ActionListener
        textField.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String input = textField.getText();
                JOptionPane.showMessageDialog(frame, "Hello, " + input + "!");
            }
        });

        // Add components to frame
        JPanel panel = new JPanel();
        panel.add(label);
        panel.add(textField);
        frame.add(panel);

        frame.setVisible(true);
    }
}

Explanation

✔️ textField.addActionListener() → Detects Enter key press.
✔️ JOptionPane.showMessageDialog() → Shows a pop-up with input.

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5️⃣ Customizing JTextField (Size, Color, Font)

Example: Styling a JTextField

textField.setFont(new Font("Arial", Font.BOLD, 14));  // Change font
textField.setForeground(Color.BLUE);  // Text color
textField.setBackground(Color.LIGHT_GRAY);  // Background color
textField.setHorizontalAlignment(JTextField.CENTER);  // Center text

✔️ setFont(new Font("Arial", Font.BOLD, 14)); → Changes font & size.
✔️ setForeground(Color.BLUE); → Changes text color.
✔️ setBackground(Color.LIGHT_GRAY); → Changes background color.
✔️ setHorizontalAlignment(JTextField.CENTER); → Aligns text inside the field.

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6️⃣ Disabling or Making JTextField Read-Only

Example: Disabling a Text Field

textField.setEditable(false);  // User cannot type
textField.setEnabled(false);  // Field is grayed out

✔️ setEditable(false); → Locks the field (user cannot edit).
✔️ setEnabled(false); → Disables the field (gray and non-editable).

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7️⃣ Limiting Input Length

By default, JTextField does not restrict input length. You need to manually limit it.

Example: Restricting Input to 10 Characters

import javax.swing.*;
import javax.swing.text.*;

public class JTextFieldLimitExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("JTextField Limit");
        frame.setSize(300, 150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JTextField textField = new JTextField(20);

        // Limit input length to 10 characters
        ((AbstractDocument) textField.getDocument()).setDocumentFilter(new DocumentFilter() {
            public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException {
                if ((fb.getDocument().getLength() + string.length()) <= 10) {
                    super.insertString(fb, offset, string, attr);
                }
            }

            public void replace(FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
                if ((fb.getDocument().getLength() + string.length() - length) <= 10) {
                    super.replace(fb, offset, length, string, attr);
                }
            }
        });

        frame.add(textField);
        frame.setVisible(true);
    }
}

✔️ Uses DocumentFilter to restrict input length.

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8️⃣ Using JTextField with JButton

Example: Get Text When Clicking a Button

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

public class JTextFieldButtonExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("JTextField & JButton");
        frame.setSize(300, 150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JTextField textField = new JTextField(15);
        JButton button = new JButton("Submit");
        JLabel label = new JLabel("Enter something:");

        // Add ActionListener to button
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String input = textField.getText();
                JOptionPane.showMessageDialog(frame, "You entered: " + input);
            }
        });

        // Add components to frame
        JPanel panel = new JPanel();
        panel.add(label);
        panel.add(textField);
        panel.add(button);
        frame.add(panel);

        frame.setVisible(true);
    }
}

✔️ button.addActionListener() → Reads JTextField input when clicked.
✔️ Displays user input in a dialog box.

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🔥 Summary

✅ JTextField allows single-line text input.
✅ Use getText() & setText() to read and change text.
✅ Handle Enter key events with ActionListener.
✅ Customize with fonts, colors, alignment, and size.
✅ Combine with JButton for interactive input handling.
✅ Limit input length using DocumentFilter.