What is the difference between an int and an Integer in Java and C#?

Question

I was reading More Joel on Software when I came across Joel Spolsky saying something about a particular type of programmer knowing the difference between an i

Answer 1

int is used to declare primitive variable

e.g. int i=10;

Integer is used to create reference variable of class Integer

Integer a = new Integer();

Answer 2

There are many reasons to use wrapper classes:

1. We get extra behavior (for instance we can use methods)
2. We can store null values whereas in primitives we cannot
3. Collections support storing objects and not primitives.