Add Image Using Image Icon Label

Add Image Using Image Icon Label#

An ImageIcon in Java is a class from the javax.swing package that encapsulates an image to be used in Swing components. When paired with a JLabel, it enables the display of images within the graphical user interface.

Definition and Purpose#

ImageIcon is a subclass of javax.swing.Icon.
It is typically used to load and manage images (like .jpg, .png, .gif) and render them in UI elements.

Common Uses#

Display in JLabel: Most common use. Assign an ImageIcon to a JLabel to show an image:
```
JLabel label = new JLabel(new ImageIcon("path/to/image.jpg"));
```

Buttons and Menus: Used to add icons to JButton, JMenuItem, etc.

JButton button = new JButton(new ImageIcon("icon.png"));

Toolbars: Icons in JToolBar often use ImageIcon.

Key Features#

Supports image formats via Java’s built-in ImageIO.
Handles automatic repainting of components when icons change.
Can be created from files, URLs, or byte arrays.

Reference#

Java SE Documentation: ImageIcon

Example Code#

/*
 Developer: James Goudy
 Description: A simple Java Swing application to read and display an image using a JLabel.
 */

 package filereading;


 import java.awt.Image;
 import java.awt.image.BufferedImage;
 import java.io.IOException;
 import java.net.URL;
 import javax.imageio.ImageIO;
 import javax.swing.*;
 
 public class FileReading {
 
     public static void main(String[] args) {
         SwingUtilities.invokeLater(ImageViewerFrame::new);
     }
 }
 
 class ImageViewerFrame {
     
     
     // global variables
     private BufferedImage image;
 
     private final JFrame frame;
     
     private final JMenuBar menuBar = new JMenuBar();
     private final JMenu fileMenu = new JMenu("File");
     private final JMenuItem quitItem = new JMenuItem("Quit");
     
     private final JLabel imageLabel = new JLabel();
 
     
     // constructor
     public ImageViewerFrame() {
         
         
         frame = new JFrame("Image Viewer");
 
         // helper functions
         setupMenu();
         setupFrame();
         loadImage("/images/dog6.jpg");
         setupImageLabel();
 
         frame.setVisible(true);
     }
 
     private void setupMenu() {
         
         // setup quit menuitem
         quitItem.addActionListener(e -> System.exit(0));
         
         // add quitItem to the menu
         fileMenu.add(quitItem);
         
         // add menu to memubar
         menuBar.add(fileMenu);
         
         // add menubar to Frame
         frame.setJMenuBar(menuBar);
     }
 
     private void setupFrame() {
         
         // frame dimensions
         int width = 800;
         int height = 600;
         
         // set what happens on close
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         
         // set framesize layoutmanager and screen location
         frame.setSize(width,height);
         frame.setLayout(null);
         frame.setLocationRelativeTo(null);
     }
 
     private void loadImage(String filePath) {
         
         try {
             URL imageUrl = getClass().getResource(filePath);
             
             // test for  file path
             if (imageUrl == null) {
                 
                 // show error pane if not found
                 JOptionPane.showMessageDialog(frame, 
                                "Image not found: " + filePath,
                                "Error", JOptionPane.ERROR_MESSAGE);
                 return;
             }
             
             image = ImageIO.read(imageUrl);
             
         } catch (IOException e) {
             // show error pane
             JOptionPane.showMessageDialog(frame, 
                     "Failed to load image: " + e.getMessage(),
                     "Error", JOptionPane.ERROR_MESSAGE);
         }
     }
 
     private void setupImageLabel() {
         
         int width = 300;
         int heigth = 200;
         
         if (image != null) {
             
             // scale image
             Image scaledImage = image.getScaledInstance(width, heigth, Image.SCALE_SMOOTH);
             
             // add image to image icon
             ImageIcon icon = new ImageIcon(scaledImage);
             
             imageLabel.setIcon(icon);
             
             // center the picture on the label
             imageLabel.setHorizontalAlignment(SwingConstants.CENTER);
             imageLabel.setVerticalAlignment(SwingConstants.CENTER);
             
             // set image location and size
             imageLabel.setBounds(50,50,width, heigth);
             
             // add imagelabel to frame
             frame.add(imageLabel);
         }
     }
 }
 

The build sequence of this Java Swing program involves several key steps that follow a clear flow from application startup to GUI rendering. Below is a breakdown of the execution (build) sequence from class loading through GUI display:

1. Application Entry Point#

The main method in the FileReading class is the entry point:
```
SwingUtilities.invokeLater(ImageViewerFrame::new);
```
This line schedules the creation of a new ImageViewerFrame instance on the Event Dispatch Thread (EDT), ensuring thread safety for Swing components (ref: Oracle Swing Tutorial).

2. Construction of `ImageViewerFrame`#

The constructor of ImageViewerFrame is called:

public ImageViewerFrame() {
    ...
    setupMenu();
    setupFrame();
    loadImage("/images/dog6.jpg");
    setupImageLabel();
    frame.setVisible(true);
}

It initializes the GUI step-by-step:

a. `setupMenu()`#

Initializes menu components:
- Adds “Quit” menu item with action listener to terminate the application.
- Adds the menu item to the menu, then attaches the menu bar to the JFrame.

b. `setupFrame()`#

Sets up the frame:
- Dimensions, close operation, layout manager (null = absolute positioning), and centering the window on the screen.

c. `loadImage(String filePath)`#

Attempts to load an image from the classpath using getClass().getResource(filePath).
If successful, loads the image into a BufferedImage via ImageIO.read.
Displays error dialogs if the image is not found or cannot be read.

d. `setupImageLabel()`#

If the image is loaded:
- Scales it to 300×200 using Image.SCALE_SMOOTH.
- Wraps the scaled image in an ImageIcon and sets it on a JLabel.
- Positions the label on the frame with absolute coordinates.
- Adds the label to the frame.

e. `frame.setVisible(true)`#

Displays the fully constructed GUI window.

Key Notes#

Absolute positioning (null layout manager) is used, so components are manually sized and placed.
Classpath resource loading: The image must reside in /images/dog6.jpg relative to the classpath root.
The use of invokeLater() aligns with Swing’s requirement to create and update GUI components on the EDT for thread safety.

Would you like a diagram of the object construction and method call sequence?

Add Image Using Image Icon Label

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