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Fax initialized age

in this video we're going to look at some fundamental variable operations in Java we're going to look at this declaring initializing in assigning a variable I'm also going to point out a few gotchas that tend to trap people when their early programming and it makes them just simple mistakes I want to tell you what those are so that you can be sure to avoid them so first of all why variables we require variables quite a bit in programming because it's a place to store our work maybe we're gathering some data from the user maybe we're submitting some data from a phone to a server a server in the cloud maybe we're doing some kind of computation or some kind of driving directions all of these require temporary variables or in other words something that is just used for kind of an in-flight calculation and won't actually be persisted to permanent storage they could eventually be persisted don't get me wrong and most things are going to be in a temporary variable before they're persisted but we're not worried about persistence right now our concern at the moment is temporary memory or RAM random access memory the memory which essentially cleans itself out each time the computer stops now don't worry though that the data types we talk about are going to be important when we talk about persistence as well but that's a future topic so scope is important and if you're new to programming scope might be kind of something that's not very clear but scope is defined by the curly braces on an American keyboard you see these to the right of the P key in these curly braces indicate a boundary essentially a boundary of work that's going to be done now they're curly braces I kind of think it looks like the head of a toothbrush which i think is a good analogy as well because when I wake up in the morning one of the first things I do is brush my teeth when I go to bed at night one of the last things I do is brush my teeth so brushing my teeth is essentially if a boundary of everything that I'm going to fit into my day it starts with brushing my teeth it ends with brushing my teeth and that's what these Curly's mean if I look at the program that we wrote earlier in NetBeans we see that we have this thing called a class and we might not know what a class is yet but you see that it's boundary is defined by the open and closed curly and then we also have a method and again we might not know what a method is yet but not not to worry we can't see the boundary that is defined by the open and closed curly there's a matter as a matter of fact when I click on a closed curly it highlights the corresponding open curly in yellow in vice versa it does the same when I click on an open curly so we know scope is important because that tells us what type of variable we are declaring in attribute an attribute is a variable that is declared within the class but not within a method in other words this is a method this is the class so an attribute could be defined pretty much anywhere where I've highlighted here we wouldn't define it in the Javadoc so anywhere I've highlighted here in theory it could also be where I've highlighted down here and practice these attributes are typically defined at the very top of the class now I will say that we call them attributes but there are other acceptable names like field or member variable depending on when you learn java we've used different words to describe this type of variable but they're all the same a parameter variable is a variable that's inside of a method signature like the one that we see here string args now here again if we don't know what a method is yet that doesn't make a whole lot of sense but just to remember this a parameter variable is in between the parentheses that make up a method when we talk more about methods that will make a bit more sense a local variable is a variable that is declared within a method like so so a local variable is declared anywhere within this open and close curly for a method it can also be local to an if block or a for loop we don't know what those are yet so don't worry but again we'll get to those in a bit later now careful here the only place where we can declare any kind of variable is within the class itself in other words within the open curly closed curly that I've highlighted here in this snippet we simply cannot declare variables above the class where after the class that's a pitfall that I see many times for new programmers someone might say oh okay well int age equals 40 like so you see it doesn't belong there because it's outside of the class so when declaring a variable make sure that you are declaring it inside of a class or inside of a method or even inside of a a method signature but it simply cannot be declared outside of a class note it will give us a red line the right thing to do when we have a red line is to stop and fix our issue okay vocabulary so different vocabulary applies to variables declaring a variable is something that we do only one time and to declare a variable we need a name and a type although actually those go in reverse order it would be a type and then a name one of the types that we can have is int which is a whole number type so you see int age that is a variable declaration I am declaring the variable age and that's name that I just made up and I'm saying it is type int now we'll get into datatypes in a separate video but datatype simply says okay we have Brandon's binary calculator that we saw in a previous video we know that we can use a set of zeros and ones to come up with some kind of number like if I put let's see if I put the one here that will make one 51 51 just like so if I put a 1 in the 8 it will make 1 51 159 and so the datatype simply says how do we interpret that 159 is it a whole number or is it a key that takes us to a map of numbers to letters so we can figure out what letter corresponds to that number that's what that datatype means okay so declaration means we have type and name okay and we go back and we see that assignment means we're assigning a value to this variable so I can say age equals 40 again that's an assignment so let me go ahead and say declare and then we'll put a comment that says assign now can I assign a value to a variable multiple times and the answer is yes so I'm gonna do a system.out.print line which says age and then plus age now you might say gosh what's that well we don't we might we've seen this in a prior video but system.out.print line just means print something to standard output you see something funny here where I've taken something in quotes that means just print what is inside of those quotes literally then I have a plus and then I have my variable age it doesn't mean we're adding things together it means we are printing what's between the quotes and then we're printing the value of this age variable so let me go ahead and run this before I continue so we'll go ahead and choose run and let's see we should get a message down here when we run it says age 40 and sure enough that's coming from here age and then the value of 40 which is what we see here okay so can I assign the question was can I assign a different value to that variable let's say age equals 42 all right yeah I'm allowed to do that no problem a variable can be reassigned an infinite number of times in the life of that variable so if I run we'll see now we'll have two similar lines age 40 and age 42 both using the same variable and I said that we can assign a different value to a variable over time as many times as we want that's why it's called a variable because the data inside of the variable varies or in other words it can change okay so assignment we can do as many times as we want an assignment can even be a mathematical expression we could say h equals h plus 3 and if i run the program now remember that's assignment not equality it's saying take what's on the right perform that calculation assign it to the variable on the left so if i run now we see age 40 and then 40 plus 3 is 43 so age 40 and age 43 so assignment we can do multiple times but be careful we cannot declare more than once a pitfall that I see frequently is that somebody will do something like declare the variable age and then continue to put the type before the variable each time that variable is used you can't do that because the simple nature of having the type before the variable name means you're declaring that variable now what's the big deal declaring a variable means you are allocating space and memory for the data that you're storing in this variable that space has to have a unique name so if you tried to declare the same variable over and over again with the same name it's going to give you a red line and say no can do buddy you can't keep declaring more spaces in memory with the same name but if I don't have that data type in front it means that I'm not trying to allocate a new place in memory I'm trying to reuse the one I allocated up above when I had int age okay we'll go ahead and say that so no big changes there I do want to consider initialization initialization is the very first time that you that you assign a value to a variable so I could say something like and let's say zip code although that's a purely American concept because a lot of a European zip codes contain letters so that should really be a string but nonetheless in sub code or they did be a postcode over there zip code equals four five two oh two okay you see what I've done here is I've declared the variables of code and I've assigned four five - OH - to that variable zip code because I've done the Declaration and the initial assignment all in one step this is also known as initialization or initializing that variable and just like anything else I can do a system.out.print line and say zip code zip is actually an acronym and then we'll say zip code now zip code see I could I I'm tempted to make that an uppercase C I really feel like that should be an uppercase e and by the way note that it is case-sensitive so if I have a lowercase C here an uppercase C here it tells me cannot fine symbol cannot find symbol means I'm trying to access a variable that has never been declared before and if you're looking at this especially as a newer program or you might say I don't understand it zip code he wrote zip code there what's the difference well Java is case-sensitive so we have to make sure that the case is exactly the same when we declare the variable and when we wish to use the variable by the way I said it is an acronym do you know what it stands for zone improvement program so zip code for five - OH - there we go so that's declaring and initializing a variable also we took a look at assigning a variable and using some mathematic computations for assigning a variable okay declaring a variable we know we need the type and then we need a name so the type can be any one of eight primitive types that we'll talk about in a separate video those are byte short int long double float boolean and car CH AR car we can also use a string which is kind of a special type one that represents multiple letters or numbers and then we can also use a class we may or may not know what a class is right now so don't worry about that if you don't know what it is now for the name the name has to be unique and that's why I say you can only declare a variable with a given name one time you cannot declare it more than one time with the same name the name needs to be made of letters and numbers and the underscore we typically use the underscore only in a special type of variable called a constant usually the first character of a variable has to be a letter so in Java we will typically use lower camelcase to name variables so you see the first word all over case no space no underscore between the first word in the second word the second word upper case the first letter the third word upper case the first letter all else is lowercase so lower camel cases are standard in Java now could you use a different case could I make it uppercase zip code like so yes as long as I'm but the thing is you kind of look like the new guy when you do that so it's one of those things where it would work if you used a whole bunch of crazy underscores and things like that but your colleagues will say what are you doing it's a bit more readable to just use lower camelcase which is the standard that we have for variables so that's a look at variables in our next video we'll look at the different variable types I look forward to seeing you then thank you