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Siva Nookala - 16 Feb 2019
Variables can be used to store information/data. Once a variable is declared, it can be initialized with some value and later can be changed to some other value. A variable can be used further for performing any calculations, printing it etc., Every variable should have a datatype like int, boolean etc., and that type should be specified at the time of declaring the variable. Every variable should also have a unique (or non duplicate) name to identify it.

For example, in a student program we can have one variable to store 'the section of the student', one for 'roll number' etc.
char section;
int roll_number;
Here char tells the data type of the variable and section gives the variable name. Similarly int is the data type and the variable name is roll_number. You can assign a value to a variable at the same time that it is declared. This process is known as initialization.
char section = 'C';
int roll_number = 76; //assign 76 to roll number
Here int defines the data type of the variable and roll_number gives the variable name, where 76 is the current value of the variable. As shown above, one variable (roll_number) in your program can store numeric data while another variable (section) can store char data. Java has special keywords to signify what type of data each variable stores. We can declare variables using the keywords/types explained in Data Types In Java and initialze the value of the variable.

Rules for naming variables:

  • No spaces in variable names
  • No special symbols in variable names such as !@#%^&*
  • Variable names can only contain alphabets, numbers, and the underscore ( _ ) symbol
  • Variable names can not start with numbers, but variable name can contain numbers
  • Variables are case-sensitive, numberOfStudents is different from Numberofstudents, NUMBEROFSTUDENTS, numberofstudents etc.,
Valid variable names section
Invalid variable names 3idiots


name with spaces


Lets see a simple program using the variables.
Print variable value
class PrintVariableValue
    public static void main(String arg[])
        int numberOfStudents = 34; // LINE A
        int highestMarks = 98;
        System.out.println("The class has " + numberOfStudents + " students and the highest marks are " + highestMarks + ".");    

The class has 34 students and the highest marks are 98.


Here we declared variables numberOfStudents and highestMarks. Both of them are of type int. We have concatenated varialables and strings to print the formatted output.

  • Change the numberOfStudents to 56 and highestMarks to 25 and observe the output.
  • Add one more double variable averageMarks and set it to 53.2. Print the average marks in the format "Average marks are 53.2".
  • In LINE A, change the variable name from numberOfStudents to numberofstudents (change O and S from capitals to small letters) but do not change it in the print statement. Observe the compilation error you get. Note that the variable names are case-sensitive.
  • Try declaring the variables with names like 3idiots, v@r## and number of students and see what compilation errors you get.

4-min video about Java Variables

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