According to the specs J2SE 1.4.2 and 5.0:
Component.setFocusTraversalKeys(int id, Set keystrokes)
"Throws: IllegalArgumentException - .. if any Object in
keystrokes is not an AWTKeyStroke"

However, the J2SE implementations 1.4.2 and 1.5.0 throw ClassCastException
instead of expected IllegalArgumentException.

The code sample below demonstrates the problem:
-------------- TestFT13.java -----------------
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class TestFT13 {
    Button button = new Button();

    public static void main(String[] args) {
        new TestFT13().test();
    }

    private void test() {
        AWTKeyStroke key = AWTKeyStroke.getAWTKeyStrokeForEvent(
            new KeyEvent(button, KeyEvent.KEY_PRESSED, 0, 0, KeyEvent.VK_UNDEFINED, 'a'));
        HashSet set = new HashSet();
        set.add(key);
        set.add(new Object());

        try {
            button.setFocusTraversalKeys(
                   KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set);
        } catch(Exception e) {
            if (e instanceof IllegalArgumentException) {
                System.out.println("Component: OKAY");
            } else {
                e.printStackTrace();
                System.out.println("Component: unexpected " + e + " thrown instead of IAE");
            }
        }
    }
}
---------------------------------------------------
-------------- Output for 1.4.2 -------------------
e:\c:\jdk1.4.2\bin\java -classpath . TestFT13
java.lang.ClassCastException
        at java.awt.Component.setFocusTraversalKeys_NoIDCheck(Component.java:5802)
        at java.awt.Component.setFocusTraversalKeys(Component.java:5742)
        at TestFT13.test(TestFT13.java:20)
        at TestFT13.main(TestFT13.java:9)
Component: unexpected java.lang.ClassCastException thrown instead of IAE
---------------------------------------------------

###@###.### 2004-11-16 11:00:40 GMT