Question

I have simple test project which creates a frame and adds one JTextPane to it

When I select text and move mouse within JTextPane area all is fine, but when mouse leaves JTextPane area and I continue moving mouse up and down I have low performance. Selection is not smooth.

Is it normal for Java programs?

What should I do to fix this issue?

The code and result shown on image below

public class Main {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() { 
            @Override
            public void run() {
                Application app = new Application();
                app.run();
            }
        });
    }
}

class Application {
    protected JFrame frame;

    public Application(){
        frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void run(){
        init();
        showFrame();
    }
    protected void init(){
        frame.setSize(new Dimension(1000,700));
        JTextPane textpane = new JTextPane();
        frame.add(textpane);
    }
    protected void showFrame(){
        this.frame.setVisible(true);
    }
}

Answer 1

Add the JTextPane to a JScrollPane and add the scroll pane to the frame.

Edit:

Misunderstood your issue. Yes, I do notice that the selection is a little slower.

See the JComponent.setAutoscrolls(…) method. As the API says:

synthetic mouse dragged events are generated when the mouse is dragged outside of a component’s bounds and the mouse button continues to be held down

I guess the generation of these synthetic events is not as fast as the generation of a normal event so the selection isn’t as smooth. I don’t think there is anything you can do about this.