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

In platforms like Java, ints are primitives while Integer is an object which holds a integer field. The important distinction is that primitives are always passed around by value and by definition are immutable.

Any operation involving a primitive variable always returns a new value. On the other hand, objects are passed around by reference. One could argue that the point to the object (AKA the reference) is also being passed around by value, but the contents are not.