Why are there so many types of number in Java when long and double work every time?

Question

Now I have been trying to learn Java Programming, I want to know why do we use things like Float, short, and int when we could be just be

Answer 1

If you know the bounds of the data you're trying to hold then it makes sense to use the smallest possible primitive data type that can hold it. This is going to always be more memory efficient than allocating more memory than you need.