This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
JTextField does not support styled content. The 'setDocument' method is used mainly for extensions of PlainDocument designed for input constraint (like the newer DocumentFilter) as shown in the api. JTextPane is the minimum choice for text styling.