Technically, this is not a valid URL. Spaces are not a valid character in URLs and must be [encoded](http://en.wikipedia.org/wiki/Percent-encoding) as `%20` (or `+`, under classical rules).

The Stack Exchange markdown engine applies heuristics to determine the end of a URL; it allows some characters to go unencoded, including balanced parentheses and commas, but doesn't go as far as to allow spaces. I don't think the engine should change to accommodate spaces.

This is arguably the job of your browser. When I copy the URL from the Firefox URL bar to the clipboard, Firefox helpfully copies it as

    http://docs.oracle.com/javase/7/docs/api/java/awt/geom/Rectangle2D.html#intersects%28double,%20double,%20double,%20double%29

Chrome, on the other hand, copies

    http://docs.oracle.com/javase/7/docs/api/java/awt/geom/Rectangle2D.html#intersects(double, double, double, double)

to the clipboard. The minimum you have to do to change this to a sufficiently-valid and working URL is to replace the spaces by plus signs:
    http://docs.oracle.com/javase/7/docs/api/java/awt/geom/Rectangle2D.html#intersects(double,+double,+double,+double)

Alternatively, you can use the hyperlink editor tool (press <kbd>Ctrl</kbd>+<kbd>L</kbd> or click on the corresponding button in the editor toolbar). This tool performs the necessary conversion (it escapes all special characters).