Suppose you have a web form that allows users to upload JPG, GIF or PNG images. Before you store the images in your system, you want to convert them all to the JPG format. Design an image converter API. Sketch out all classes and interfaces that are involved.

Note: the actual code necessary to convert a JPG image to a GIF image is not the point. Just place a comment at the appropriate location where the actual conversion should occur.

What is a design pattern and why are they useful in software development?

Describe the singleton design pattern and how you might use it in practice.

Implement it.

Describe the Factory design pattern and how you might use it in practice.

Implement it.

Describe the Observer design pattern and how you might use it in practice.

Implement it.