Just to be clear, I am referring to boxing and autoboxing in Java.

But first, we need to talk about the elephant in the room, that is the wrapper classes.

You know people say Java is 99% Object Oriented. That is because not all things are extending the Object class, Java also supports primitve data-types like int, char, long etc. This is good because we dont need to store them in the memory-heap like other objects, this makes things faster.

This is where Wrapper class comes in. For every primitive type we have a class. This class extends the Java object.

Like:

1. int -> Integer
2. char -> Char, etc

Coversion of a primitve value to an Object type is called boxing,i.e. primitive --> Class == Boxing. So something like this:

Integer num1 = new Integer(8); //boxing

is called boxing. However such a syntax is an old fashioned way to write, the better way to write is:

Integer num1 = 8; //auto-boxing

and this is called autoboxing!

Similarly, going from Object type to primitive type is called un-boxing. This is what it looks like:

int num2 = num1.intValue(); //unboxing

or

int num2 = num1; //auto-unboxing

Converting string to int:

String str = "12";
int num3 = Integer.parseInt(str); //num3 becomes 12

Note: While using the collections framework, you can never use primitives, you mandatorily need to use Wrapper Classes, because Generics require reference types and not primitive types. i.e. List<int> is not allowed, only List<Integer> is allowed.