JEditorPane.setPage(URL) loads the provided URL asynchronously.

The old pageLoader is not cancelled when the new stream is opened synchronously (p < 0). In this case, a synchronized block is used to assign the new value to pageLoader.

In the asynchronous case (p >= 0), the pageLoader.cancel is called but no synchronization is used, pageLoader could become null right after the code entered the corresponding if-block.

The new value is assigned to pageLoader without synchronization.