Declaring, initializing and using variables in Java

Module 1: Declaring, initializing and using variables.

  

Objectives

• Identify the uses for variables and define the syntax for variables.
• 8 different types of java programming language primitive data types.
• Declare, initialize, and use variables and constants according to java programming language guidelines and coding standards.
• Modify variable values using operators.
• Using promotion and type casting.

1. Identify the uses for variables and define the syntax for variables.

Variable can be declared in java in 2 different places:

• In body of a method – in this case, the variable will be local to that method & exist only during the execution of that method.
• Class definition – in this case, the variable will be declared outside of any method body and such variable are called instance / attribute variables.

In the above example, we hve 5 attribute / instance variables, since they are declared outside of any method body, but inside the class Shirt. These variables come into existence when the object of the class are created and each object of the class will have its own set of these variables. On the right side of the above figure, there are 3 shirt objects. Each shirt object has its own shirt ID, price, color, description, quantity in stock variables.

These variable declarations can exist anywhere within the class body as long as they are not in any method body. Typically they are put first in the class, before any method declaration. But they can actually come after method declaration, between method declaration or anywhere in class definition as long as they are not in a method body.

  

Variable declaration and intialization:

Attribute / instance variable syntax:

[modifiers] type identifier [=value];

• [modifiers] -> optional – These are special Java keywords that modify the way the variable functions. ex: public, static etc.
• type -> required – This specifies the type of information or data held by the variable. ex: int, float etc can be either primitive or can be object reference type.
• identifier -> required – This is the name that you assign to the variable.
• [=value] -> optional – This is an initial value that u may want to assign to the variable. It should match with the type of the data that we have specified.
  

The variable declaration / initialization should end with ‘;’ semi-colon.

  

Describing primitive data data types: