How to work with text fields in Swing

A text field in Java Swing is a graphical user interface component that allows users to enter text. Swing offers the JTextField class, a subclass of JComponent, to construct and manage text fields. Let’s look at different ways to use text fields in a Swing application.

JTextField library import

The JTextField utility is part of the Java Swing library. To import JTextField we can write the following:

import javax.swing.JTextField

Constructors of the JTextField class

To generate text fields with varying starting attributes, the JTextField class offers a variety of constructors. The most popular builders are listed below:

1. JTextField(): This constructor generates a text field that contains no initial text or icon.

2. JTextField(String text): This constructor produces a text field with the starting text.

3. JTextField(String text, int columns): This constructor generates a text field with the provided beginning text and the requested number of visible columns (width), where the columns parameter refers to the number of characters that the text field can display horizontally.

Commonly used methods of the JTextField class

Let’s explore some commonly used methods of the JTextField class that enable us to interact with text fields:

Code example

Let’s create a simple Swing application that demonstrates working with a text field and a button. In this example, the user enters text into a text field, and when the “Set Text” button is clicked, the entered text is updated in all the other text fields.

We have used the JFrame utility to render our text fields in the GUI. It provides a windowed container for creating GUI applications. Refer to the official documentation of JFrame to learn more about it.

Output

The output of the code above will look like this initially:

Enter some text in “Text Field 1:” and press the “Set Text” button. You’ll see the results updating in all the text fields, i.e., the value of the other two text fields will be changed to the value we entered.

Code explanation

• Lines 1–4: The code starts by importing essential packages javax.swing and java.awt for creating GUIs and handling essential AWT functions.

• Lines 7–11: The main method is the program’s starting point.

• Line 8: SwingUtilities.invokeLater ensures that the GUI components are constructed and shown on the Event Dispatch Thread (EDT) for proper handling.

• Line 13: The createAndShowGUI method establishes Swing GUI components and interactions, encapsulating the application’s core logic.

• Lines 14–16: The JFrame is the application’s main window. A new JFrame, titled “Text Fields Example,” is created to present the user interface. setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) defines how the application behaves when the user closes the window. setPreferredSize(new Dimension(600, 400)) sets the frame’s preferred size to $600$x$400$ pixels, shaping its appearance.

• Lines 18–22: A JPanel called panel is crafted using GridBagLayout for flexible grid arrangement. GridBagConstraints configure component alignment in the grid, while gridx and gridy set the starting cell, whereas Insets provide external padding for components.

• Lines 32–45: The provided lines introduce labels and text fields to the panel utilizing GridBagConstraints. The command constraints.gridy++ advances the grid row for subsequent components. Employing panel.add(new JLabel("Text Field 1:"), constraints), a label is appended for “Text Field 1.” The subsequent line panel.add(textField1, constraints) incorporates textField1 within the same row. This pattern is replicated for textField2 and textField3 placements.

• Lines 47–50: An ActionListener named listener responds to Enter key presses by retrieving the source text field and displaying the entered text in a message dialog.

• Lines 52–54: The listener is subsequently applied to each text field using addActionListener(listener).

• Lines 56–61: A JButton named setTextButton is generated, featuring the label "Set Text" To determine the button’s size, setTextButton.setPreferredSize(new Dimension(150, 30)) is invoked. Simultaneously, constraints.gridy++ facilitates the shift to the succeeding row, while constraints.gridwidth = 2 enables the button’s expansion across two columns. By utilizing constraints.fill = GridBagConstraints.HORIZONTAL, the button attains a horizontal stretching effect. This refined button is subsequently incorporated into the panel.

• Lines 68–71: The content pane is designated within the frame to finalize the layout. The frame’s dimensions are optimized via frame.pack(), and its placement at the screen’s center is ensured with frame.setLocationRelativeTo(null).