4.1. Declaring Variables

Sometimes you know you will need a variable in your program but you won’t have a value to give it right away. That’s ok! Your computer is totally down for you to create a variable that doesn’t have a value associated with it just yet.

When you create a variable for the first time, regardless of whether or not you assign it to a value right away, we say we are declaring a variable. When you are declaring a variable, it is important that you do not include any spaces in your variable’s name or any numbers at the very beginning of the name 1. Here’s an example of what it looks like to declare two different variables, both of which have valid names and are not assigned to any values.

  1. int score;
  2. double percentChange;

Again, these are statements2. We are telling our computer that we would like to create two variables, one with the name score and one with the name percentChange. Here is how our computer might interpret these two lines of code:

Notional Machine variables 2

Notice that there isn’t any value in the box yet? That’s because we haven’t told our computer to assign a value to either of these names.

Now, in your Algebra class, it’s kind of assumed that the values that variables can store are numbers — makes sense, it is a math class after all. However, in computer science, the collection of values that a variable can store is much larger. We will learn about all of these values over the next few weeks. For now, we’re going to stick with what we know, numbers!

I want you to notice the strange little int word in the example above. This keyword tells our computer what type of value can be found in the variable. In this example, we are telling our computer that it can expect an integer to be assigned to the variable score.

The second variable has the keyword double out front and this is how we tell our computer that we plan to store a decimal value in a variable.

Java is a HELLA picky language, so we ALWAYS have to list the type of the value we plan on storing in a variable 3. You cannot change your mind later or try to slyly store a different value type in the variable; once a variable is declared, it will forever be that type! Need a different type? Well tough! You’re gunna need to declare a new variable with a different type.

What happens when you’re ready to give your variable a value? Keep reading to find out. :D


This is the pattern you should follow if you want to declare a variable:
type name;


10score and percent Change are not valid variables names because the first one includes a number out front and the second includes a space. Want to know more about naming variables? Check out this website!


Notice the semi-colons at the end?


Computer scientists call hella picky languages like Java “statically typed” languages. I guess it sounds a little more professional that way. :P