title: How to indicate that a column in a table is sortable (UI design question)?
body: <p>In the application that I am working on, there is tabular data (for the record, it is a Java Swing app using <code>JTables</code>). In some cases the data is sortable by clicking on the column headers.
  What I want to know is what is a good way to indicate to the user if a given column is sortable or not?</p>
  
  <p>I have come up with the following possibilities.</p>
  
  <p>1) Put an icon in each sortable column indicating it is sortable. I personally do not like this option.</p>
  
  <p>2) Change the mouse cursor into something else when it hovers over the header to indicate it is sortable.</p>
  
  <p>3) Put a note in the tooltip text when hovering over the column saying that it is sortable.</p>
  
  <p>Does anyone have any other suggestions? </p>
  
  <p>Update:</p>
  
  <p>I think a clarification is in order.
  My question is <strong>not</strong> how does one indicate that a given column is <strong>currently</strong> sorted. That is already implemented via the up/down sort triangle paradigm.
  I want to give the user a clue as to which columns <strong>can</strong> be sorted before they click on the header to sort it.</p>
  
  <p>Update 2:
  I think I should explain why I'm not entirely sold on option #1. It seems to me that if one is going to put an icon to indicate which columns <strong>are</strong> sortable then this will add to visual clutter. In such cases, sometimes the UI changes on "mouse over". Case in point: Windows Vista and 7 allows one to add a filter on a column yet the indicator for this does not appear until you hover over the header with the mouse.</p>