To customize the creation code of a Swing element in NetBeans, right-click the element and select Customize code.... In the following pop-up, click the drop-down menu next to the code snippet and select Custom creation. Then you can specify the code yourself as such:
DecimalFormat df = DecimalFormat.getInstance();
// do some manipulation to the DecimalFormat object if desired
jFormattedTextField = new javax.swing.JFormattedTextField(df);