Before we see this post let see what all we have learned in previous posts of this course.
- Making Games With Java- Introduction
- Getting Everything you need for Java
- Introduction to Java Programming
- Basic data types and Variables in java
Okay, so last
week, we discussed data structures and variables, and of course I mentioned the
different data types like the Integer, Float and Double. We also looked at some
mathematical operators, and we discussed how to perform some simple
calculations. (I really hope you practiced, like I advised. Really, do it!
It’ll stick!).
Of course the
data types I mentioned are only used for numerical data, and those aren’t even
all the numerical data types. There are quite a few more, but these three are
the ones you’ll use the most, especially when you’re still learning how to
program. While these numerical data types are useful, they won’t do much good
if you want to work with letters or text. Don’t worry, there are variables that
are made specifically for text purposes. They are known as String and Char
variables, and I will take them as one.
As an extension,
I’ll discuss another data type known as the Boolean (don’t bother too much
about what it is, I’ll explain it later).
Now before we begin,
I’ll have to deal with something that I should have mentioned in the last post
(I’m quite sorry about this. This was kind of an afterthought). So we before we
talk on Strings, we’ll need to deal with…
Operator Precedence
You’ll probably
need to reopen our last project for this. Okay, now if you had practiced the
mathematical operators like I asked (if you didn’t, well, you still need to pay
attention), you may have noticed that some of the answers that the system was
returning seemed wrong. Let me use an example, say I delete everything in the
project except the print statement, and add this:
int
answer = 100 - 75 + 23;
Now, using
BODMAS method, where the addition takes precedence over the subtraction, you
should get 2, right? But if you run it, you get 48, and then you’re like “How
did the computer get it wrong?”. Well the answer is, the computer didn’t get it
wrong, at least not technically. You see if you were to calculate without the
BODMAS method, from left to right, you would get 48.
The computer doesn’t
obey the rule of BODMAS, it has its own form of operator precedence, where it
treats the subtraction and addition operator as equals, and therefore will only
be computed in the order they’re given. If you want to get the correct answer,
you have to put the operator where you want precedence in a bracket, like this:
int
answer = 100 – (75 + 23);
…that way, it
does the addition first. Therefore, if you want the one part of the equation to
take precedence of another just put it in bracket.
Now change your
code to this:
int
answer = 100 + 75 / 20;
So using the
logic I gave, the computer should do the addition first, then the division,
which should give the correct answer, right? Well, when we run it, we get…
disappointed. Well actually, we get 103, when we should have gotten 8. And then
we ask the computer, “Hey, what gives?!”. Well, do you remember when I said
that the computer has its own rules of operator precedence, well:
RULE 1:
Multiplication and division are treated as equals, and they have the highest
precedence.
RULE 2: Addition
and subtraction are also treated as equals, but they have lower precedence.
Therefore, the
computer’s logic made it to start from the division first, before doing the
addition. To fix this, you have to put the addition in brackets, like so:
int
answer = (100 + 75) / 20;
Run it, you
should get your answer. Try practicing this with other operators, more values,
and even try changing the positions of the brackets (just for fun). You could
also try saving them into different variables as practice. And next time, when
you want to run a code and it doesn’t seem to be giving you the right output,
remember that operator precedence is very important.
Now that that’s
over…
String Variable (Though it is class in java )
Now like I said
earlier, there are variables used to store text. They can store anything from
one character to an array of characters. The ‘char’ variable stores only one
character, while the ‘String’ stores more than one character. It’s quite likely
that you’ll use the String variable more though, so more emphasis will be made
on that.
You can make a new project for this, or you can
do what I did and make a new class file in out ‘tutorialproject’. Just go to
projects, and go to the “TutorialProject’ project. Click the plus signs until
you see the package, right click it, and you should see this drop down list.
Hover your pointer over ‘New’ and click ‘Java Main Class’, and this should pop
up:
Change the
‘NewMain’ in the class name textbox to ‘StringVar’ and click ‘Finish’. Keep in
mind that if you want to run this file after doing this, make sure you use
‘Shift + F6’ as just using F6 will run the first main class you made.
Now add this to
your main method:
Note the keyword
String, showing that the data type is a collection of individual characters
(these characters can be numbers or letters). Also note that the word has a
capital ‘S’, unlike ‘int’ or ‘float’. I don’t know why this is, but just
remember it. You then give the variable names (firstName and lastName), and
input your text (I’m using my name as an example, but you can use yours). Also
note that the text we inputted is written in double quotation marks. Like the
print statement, this is to distinguish the String from regular code.
If you run it,
you should most definitely get this as your output:
If you didn’t use
my name, then you won’t get this exactly.
Now, you notice
that there’s no space between the first and last name in your output. This is
because in programming, space is also a character, and so any point that
requires spacing must be specified. Therefore, all you have to do is add this “
” in between the two variables, like this:
System.out.println("My
name is "+ firstName + " " + lastName);
The empty quotes
just represent the space character, and is basically a way of telling the
computer that there should be a space there. If you run that now, you should
see something much better, which will be this:
I’m sure there’s
really nothing much to say about this anymore, so we’ll move on.
Char Variable
Under the string variables we’ve made, add these lines of code:
Note that char
has a small letter ‘c’, and also notice the single quotes that the character is
in. You cannot have a character in double quotes, or it will show an error.
Also, you cannot save more than one character into a char variable. You can
save a character in a string variable, though, but it has to be in double
quotes.
In short, it’s:
char
firstInitial = 'V';
not:
char
firstInitial = “V”;
and:
String
firstInitial = “V”;
not:
String
firstInitial = 'V';
Also, the dot I
put between the variables means that there will be a dot between them in the
output, not a space. If you run it, your result should be this:
A Quick Look on Boolean
Don’t worry,
despite the complicated look of the word, it is actually quite basic, and in
fact is something we all learn when we’re younger, though not by that name.
Boolean is a data type that stores only two values: true and false. They are
mostly used in logical operations, something that we’ll discuss in a later
post. I just wanted to give you a heads up on it.
If you want to
try it out, though, type this out on the coding window (you can comment out the
other things we’ve done first, though).
Boolean
something = true;
System.out.println(something);
Run it, and your
result should be true.
Okay, we’re
going to wrap it up here. Next time we meet; we’re going to talk more about
other forms of data structures. See you then.
If you have any issue in understanding this , Leave us a comment , will be happy to help
Thanks for reading
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