According to the Spec we should return a null if the point is not found for JTabbedPane$AccessibleJTabbedPane.getAccessibleAt(Point) class.

Cut from doc's:

getAccessibleAt

public Accessible getAccessibleAt(Point p)

      Description copied from class: JComponent.AccessibleJComponent
      Returns the Accessible child, if one exists, contained at the local coordinate Point.
      Overrides:
            getAccessibleAt in class JComponent.AccessibleJComponent
      Tags copied from class: JComponent.AccessibleJComponent
      Parameters:
            p - The point defining the top-left corner of the Accessible, given in the coordinate space of the object's parent.
      Returns:
            the Accessible, if it exists, at the specified location; else null


Look at the standard output from execution of testcase.

TestCase:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.accessibility.*;

public class GetAccessibleAt extends JFrame {
  private static Point point1 = new Point(5,10);
  private static Point point2 = new Point(95,10);
  private static Point point3 = new Point(-1,-1);
  static JTabbedPane jp = new JTabbedPane();

  GetAccessibleAt() {
    super("Test Me");

    Container contentPane = getContentPane();
    jp.add("Panel One",new JPanel());
    jp.add("Panel Two",new JPanel());

    contentPane.add(jp,BorderLayout.CENTER);
    setSize(300,170);
    setVisible(true);
  }
  
  
  public static void main(String[] args) {
    new GetAccessibleAt()
  
    
    String r1 = jp.getAccessibleContext().getAccessibleComponent().getAccessibleAt(point1).getAccessibleContext().getAccessibleName();
    String r2 = jp.getAccessibleContext().getAccessibleComponent().getAccessibleAt(point2).getAccessibleContext().getAccessibleName();
    String r3 = jp.getAccessibleContext().getAccessibleComponent().getAccessibleAt(point3).getAccessibleContext().getAccessibleName();
  
    if (r3 != null) {
      System.out.println("Test Failed!!");
      System.out.println("We should be returning a null according to the spec");
      System.exit(1);
    }
    else
System.out.println("Test Passed!!");
  }
}