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JavaFX Robot Public API

TestFX, the JavaFX GUI testing framework currently requires 4 (four) classes that are part of the JDK's private API. They are:

In order to compile the project with Java 9, we use the following flags:


If the --add-exports flags are disabled in a future Java release TestFX will require these four classes to be moved into the public API to continue working.

While these classes are probably not very useful for applications to use directly, any JavaFX application wanting to write UI tests will most likely use TestFX and thus they will indirectly be using these classes.

JavaFX internal tests also use these classes for essentially the same purpose (UI tests).

Details of Usage For Each Private API Class


TestFX Usage
ParametersImpl parameters = new ParametersImpl(applicationArgs);
ParametersImpl.registerParameters(application, parameters);

The parameters are set on a constructed Application.

Suggested Public API Replacement


 * Sets the parameters for this Application.
 * <p>
 * NOTE: this method should not be called from the Application constructor,
 * as it will return null. It may be called in the init() method or any
 * time after that.
 * </p>
 * @param parameters the parameters to set for this Application
public final Parameters setParameters(String... parameters) {
    ParametersImpl parameters = new ParametersImpl(parameters);
    ParametersImpl.registerParameters(this, parameters);

TestFX Usage
return Application.GetApplication().createRobot();

The Application class is used to instantiate a Robot.

Suggested Public API Replacement


TestFX Usage
public Image getCaptureRegion(Rectangle2D region) {
    return waitForAsyncFx(RETRIEVAL_TIMEOUT_IN_MILLIS, () -> {
        Pixels glassPixels = useRobot().getScreenCapture(
            (int) region.getMinX(), (int) region.getMinY(),
            (int) region.getWidth(), (int) region.getHeight()
        return convertFromGlassPixels(glassPixels);
private Image convertFromGlassPixels(Pixels glassPixels) {
    int width = glassPixels.getWidth();
    int height = glassPixels.getHeight();
    WritableImage image = new WritableImage(width, height);

    int bytesPerComponent = glassPixels.getBytesPerComponent();
    if (bytesPerComponent == INT_BUFFER_BYTES_PER_COMPONENT) {
        IntBuffer intBuffer = (IntBuffer) glassPixels.getPixels();
        writeIntBufferToImage(intBuffer, image);

    return image;

private void writeIntBufferToImage(IntBuffer intBuffer,
                                   WritableImage image) {
    PixelWriter pixelWriter = image.getPixelWriter();
    double width = image.getWidth();
    double height = image.getHeight();

    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            int argb = intBuffer.get();
            pixelWriter.setArgb(x, y, argb);

Pixels is used to create a screen capture.

Suggested Public API Replacement

Bypass needing to expose the Pixels class to the public API by changing the getScreenCapture method of Robot - that is, changing:

public Pixels getScreenCapture(int x, int y, int width, int height)


public Image getScreenCapture(int x, int y, int width, int height)

TestFX Usage

Essentially every method of Robot is used:

public void keyPress(int code)
public void keyRelease(int code)
public int getMouseX()
public int getMouseY()
public void mouseMove(int x, int y)
public void mousePress(int buttons)
public void mouseRelease(int buttons)
public void mouseWheel(int wheelAmt)
public int getPixelColor(int x, int y)
public Pixels getScreenCapture(int x, int y, int width, int height) 
Suggested Public API Replacement

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