Java gui code

Question

Ok i am exhausted attempting to puch usless info into my brain! My LAST CLASS before graduation is basic java but it is anything but basic - I am in need to understand and find code to list products in an generated inventory that is input by the user and given a cost and quantity - the teach just keep throwing code at us and not explaining what they are for!! im am totally lost and frustrated... can ANYONe point me to a site that has classes in a library that we can pull and manipulate to work (i can DO that ) as the real programmers do?