2.5 Jb0120: java oop: a gentle introduction to java programming  (Page 4/4)

Listing 2 shows a batch file that you can use to compile and run this program.

Using the procedure that you learned in the Getting Started module, you should be able to compile and execute this program. When you do, the program shoulddisplay 25 on your computer screen.

Variables

You will learn in a future lesson that the term variable is synonymous with the term compartment that I have used for illustration purposes in this lesson.

The important lines of code

The use of memory is illustrated by the three lines of code in Listing 1 that begin with int , beans , and System . We will ignore the other lines in the program in this module and learn aboutthem in future modules.

Declaring a variable

A memory compartment (or variable) is set aside and given the name beans by the line that begins with int in Listing 1 .

In programmer jargon, this is referred to as declaring a variable . The process of declaring a variable

• causes memory to be set aside to contain a value, and
• causes that chunk of memory to be given a name.

That name can be used later to refer to the value stored in that chunk of memory or variable.

This declaration in Listing 1 specifies that any value stored in the variable must be of type int . Basically, this means that the value must be an integer. Beyond that, don't worry about what the type means at this point. I will explain the concept of type in detail in afuture module.

Storing a value in the variable

A value of 25 is stored in the variable named beans by the line in Listing 1 that begins with the word beans .

In programmer jargon, this is referred to as assigning a value to a variable .

From this point forward, when the code in the program refers to this variable by its name, beans , the reference to the variable will be interpreted to mean the value stored there.

Retrieving a value from the variable

The line in Listing 1 that begins with the word System reads the value stored in the variable named beans by referring to the variable by its name.

This line also causes that value to be displayed on your computer screen. However, at this point, you needn't worry about what causes it to be displayed. You will learn those details in afuture module. Just remember that the reference to the variable by its name, beans , reads the value stored in the variable.

The remaining details

Don't be concerned at this point about the other details in the program. They are there to make it possible for you to compile and execute the program. You will learn about them in future modules.

Run the program

I encourage you to run the program that I presented in this lesson to confirm that you get the same results. Experiment withthe code, making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Miscellaneous

This section contains a variety of miscellaneous information.

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