Java Basics 101- Java Variables

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ATTENTION! An updated version of this article is available at http://javadevsteps.blogspot.com/2014/08/ideone-java-basics-101-getting-started.html

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Java Basics 101 – Variables

STEPS

1) Browse  http://ideone.com/VOBd7C 

IdeOne.com is an Online Compiler that allows Java Code to be written and compiled online.

We would be able to learn a lot from here without even have to install Java Development Kit to our PC.

http://ideone.com/VOBd7C 

2) Understanding Java Code Structure

2-1) Package Name

2-2) Import Declarations

2-3) Class Declaration

2-4) Method Declaration

2-5) User Instructions

http://ideone.com/VOBd7C 

3) Basic Instructions – Variable Declaration and Print Statement

As a quick start, ignore Package Name, Import Declarations and Class Declarations first.

Let’s look at basic program instructions first (Line no. 12).

Replace line No.12 with the following codes:

int first_number; System.out.println("My First Project");

Outcome:

http://ideone.com/wA5W3n 

Lesson:

- Variable is identified by its name and data type.

- Printing statement returns value to user. (in the above example it is a string)

4) Variable Assignment

public static void main(String[ ] args) { int first_number; first_number = 10; System.out.println("My First Project"); }

Outcome:

http://ideone.com/QtA0Lv 

Lessons:

- Variable can store value; a process called assignment gives a value for variable to store.

5) Print Variable Value

Change line no. 15 to the following:

System.out.println( "First number = " + first_number );

Outcome:

http://ideone.com/nKqQEw 

Lessons:

- We can combine string with variable.

- We join string and variable with join operator “+”; a process called Concatenation.

6) Variables and Data Operation

Change line no. 13 to the following:

int first_number, second_number, answer;

Change line no. 14 to the following:

first_number = 10; second_number = 20; answer = first_number + second_number;

Change line no.15 to the following

System.out.println("Addition Total = " + answer );

Outcome:

http://ideone.com/1gau2Z 

Lessons:

- You can declare many variables of the same daya type in a single statement.

- Number operation is similar to that of Mathematics.

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Moderated from: http://www.homeandlearn.co.uk/java/java_int_variables.html
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