You're right, it definitely comes from Smalltalk. For those who aren't familar with Smalltalk, you can use the ';' operator to send a sequence of messages to the same object. The example in the article would look something like this:

  mainFrame := JFrame new: 'Hello World';  
      add: label withAlignment: BorderLayout.CENTER;  
      addWindowListener: MainFrameListener new;  
      setDefaultCloseOperation: JFrame.DO_NOTHING_ON_CLOSE;  
      pack;  
      setLocationRelativeTo: nil;  
      setVisible: True;
      yourself.

(The result of a chained method expression is the result of the last method call, thus the 'yourself' message at the end so that the object itself is stored into mainFrame.)

Sigh...I miss Smalltalk.