Variables in Java

Variables are used to store values. Each variable can be treated as a box in which we can put something. The name of the box(like black box / wooden box) can be treated as the variable name. The something that we put inside the box can be treated as the value assigned to the variable.

Here is an example of creating a integer variable(age). Integer variable can store only integer values like 24.

int age = 24;

Naming Convention

Best followed naming convention of variables is to follow lowerCamelCase. It means the name starts with a lowercase letter. If there are subsequent words, they start with capital letters.

Here are some examples:

age
calculateAge
calculateFileSizeWithoutComments

Class names are in CamelCase. Example: HelloWorld. But variable names are in lowerCamelCase.

Strongly Typed

Java is strongly typed. If a type of variable is defined, the variable can accept only that type. A string value cannot be assigned to an integer variable.

int a = "hello";

Above code throws this error during build step: error: incompatible types: String cannot be converted to int.

Case Sensitive

Java is case sensitive. A variable declared using one case is different from that using different case.

int A = 10;
a = 20;

Above code throws this error: error: cannot find symbol a. That is because A and a are not same and the variable a is not defined.

Updating Variables

Once a variable is declared, we can update the value to another one of the same type.

int a = 10;
a = 20;

If the value updated is of different type, Java throws incompatible types error which we saw above.