The code snippet below shows how to change component default font.

Java Code:
public static void setUIFont (javax.swing.plaf.FontUIResource f){
    //
    // sets the default font for all Swing components.
    // ex. 
    //  setUIFont (new javax.swing.plaf.FontUIResource
    //   ("Serif",Font.ITALIC,12));
    //
    java.util.Enumeration keys = UIManager.getDefaults().keys();
    while (keys.hasMoreElements()) {
      Object key = keys.nextElement();
      Object value = UIManager.get (key);
      if (value instanceof javax.swing.plaf.FontUIResource)
        UIManager.put (key, f);
      }
    }