Adding a Scrollable JTextArea (Java)

It doesn’t work because you didn’t attach the ScrollPane to the JFrame.

Also, you don’t need 2 JScrollPanes:

JFrame frame = new JFrame ("Test");
JTextArea textArea = new JTextArea ("Test");

JScrollPane scroll = new JScrollPane (textArea, 
   JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

frame.add(scroll);
frame.setVisible (true);