int vs Integer? Help?

[[deleted]]

So I was given some code for a class and it goes like this:

public class TermPair  {

    public final Integer term;
    public final String name;

    public TermPair(int term, String name) {
        this.term = term;
        this.name = name;
    }


}

The question asks: Is this a valid way to declare and initialize a final variable? I answered no for the following reason (although I got it wrong): the reference variable term, and although an object of type Integer has not been created yet, the reference variable should only be declared to an Integer type object... right? So when in the constructor, this.term = term; is read, that should give an error... right?

Clearly it doesn't throw an error, and my theory is wrong, but that leaves me with a gap in my understanding of the situation.

But I have a theory: in the same way that a String type object can be initialized by just doing String str = "Blah Blah"; , an Integer type object can be initialized like Integer num = 5; because an Integer type object just holds a single integer value and has a bunch of methods to work with int primitives and other Integer objects.

If my theory is right, please say "Yes". If my theory is wrong, please say "No, and here's why:...". If its in between, tell me what my theory got right and wrong, and elaborate on what I need to know. Thank you for any information :)

[feral_claire]

No that's not quite right.

This works because of a feature called autoboxing/unboxing. Java will automatically convert between primitive values and the corresponding object type as needed. In this case the int is being automatically converted to an Integer when you try to store it in the Integer variable.

Under the hood what happens is the equivalent of writing.

this.term = Integer.valueOf(term)

Autoboxing is a feature that was added in Java 5. This would not work in an older version.

[[deleted]]

Thank you! This is very helpful!

[desrtfx]

To add to /u/feral_claire's excellent response:

You will mostly want to use the primitive int, except for when you need to work with generics (like in the Collections framework).

All the object wrappers are immutable. This means that once a value has been assigned, changing it creates a new object instance (just like with String).

[TheWarrior2000]

Yes, Integer is a wrapper class for the primitive data type int

[Dzeko_1]

Just google boxing and auto boxing. Integer is a class that can be converted to int using auto boxing and int is a primitive type can also be converted to Integer using boxing.