Questions about ageAsString & Parse.Int

Hiya,

Yes, the name intAsString is the name of a variable. Variables are used to store values. In this case, the value it stores is the string being read in from console.readLine() which requests user input via the keyboard. The user is asked for their age so, hopefully, they type in a number in response to that. This number is stored as a string, though, not a mathematical object. That's because of the way readLine works.

For this exercise, we want to be able to carry out mathematical operations on the user's age; we want to see if they are under 13, or not. We can't do that with a string so we must convert the contents of the variable from a string into a number. The class method parseInt can do this for us. This method takes a string object and parses it, seeing if the contents can be translated easily into an integer. There are a range of methods that do similar things; check out the documentation here.

Once parseInt has done its work on ageAsString, the value that results is then stored in the variable age which is of type int. This is a number and can, therefore, be compared to other values to see if it is greater or smaller, enabling the comparison that is required here to take place.

So, ageAsString is a variable name. This variable holds a value. The name is just for our use; it is named so that it's content is clear - it holds the age entered by the user as a string object. We could equally, but less clearly, name the variable x and it would still hold the same value, that's determined by the user's input, not the variable's name. The variable reserves an area in memory large enough to hold the data type it is assigned to. (For Strings that's not quite true as there can be some very long ones ... the memory is referenced on the fly, but for something like an integer or boolean, the memory may be referenced straight away). We access this memory by using the variable name - that variable allows us to access the data that's held in memory whether that's a string or int, or whatever - the name let's us get at the value and perform operations on it.

Using our example and taking it a little further, let's get two sets of user input:

String userName = console.readLine("What is your name?: ");
String ageAsString = console.readLine("How old are you, %s?: ", userName);

So now we have two variables holding user input. The first is the name and the second is the age. Both are strings. One holds "Steve" and the holds "21". We can call all the methods that string objects allow on both variables and values. They are both string types even though one holds just numeric characters; they are just that, characters. We couldn't perform any mathematical operations on "21" any more than we could on "Steve" - that makes no sense. "Steve" divided by 7 is what, exactly?! Same as "21" divided by seven is equally nonsensical. But once we've run the parseInt() method and passed ageAsString as a parameter, we can store that in another variable, as above:

int notMyAgeReally = Integer.parseInt(ageAsString);

Now, the variable named notMyAgeReally holds the value of my ficticious age, 21 - a number. This can be divided by seven, or whatever fantastic mathematical operation we want to do; say it's my birthday:

notMyAgeReally = notMyAgeReally + 1;
// or
notMyAgeReally++;

I digress ...

I hope that helps,

Steve.