How Can I Trigger Exceptions from the RepaintManager in Swing?

Triggering Exceptions from RepaintManager

Introduction

In your previous inquiry, you mentioned encountering exceptions that you were unable to handle within a SwingWorker thread. This article delves into the specific issue of generating exceptions originating from the RepaintManager class.

Generating RepaintManager Exceptions

1. Using CheckThreadViolationRepaintManager:

A proven approach for generating such exceptions is to employ the CheckThreadViolationRepaintManager class. This custom class extends the RepaintManager and intercepts repaint or dirty region addition operations. If these actions occur outside the event dispatch thread, it triggers an exception and prints its stack trace.

public class CheckThreadViolationRepaintManager extends RepaintManager {

    // Override methods to check for thread violations and print stack trace if found

}

2. Setting the RepaintManager:

Once you have created the CheckThreadViolationRepaintManager instance, you need to set it as the current repaint manager:

RepaintManager.setCurrentManager(new CheckThreadViolationRepaintManager());

3. Triggering the Violation:

To trigger the exception, perform repaint or dirty region addition operations from a thread other than the event dispatch thread. The exception will be thrown and printed to the console.

Example:

public static void main(String[] args) {
    RepaintManager.setCurrentManager(new CheckThreadViolationRepaintManager());

    // Create a frame and repaint it from a separate thread
    JFrame frame = new JFrame();
    SwingUtilities.invokeLater(() -> frame.repaint());
}

This code will cause the CheckThreadViolationRepaintManager to detect the repaint operation from a background thread and print an exception.

Additional Considerations

• Complete Checking: By default, CheckThreadViolationRepaintManager checks all repaint operations. You can optionally set the completeCheck flag to false to only check repaints of visible components.
• Ignoring Certain Threads: You can customize the violation detection by overriding the violationFound method in CheckThreadViolationRepaintManager to ignore specific threads, such as SwingWorker threads.

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