DATA TYPES OF JAVA

IDENTIFIRES: Identifiers are the names of variables, methods, classes, packages and interfaces. Unlike literals they are not the things themselves, just ways of referring to them. In the HelloWorld program, HelloWorld , String , args , main and println are identifiers.

It must begin with either a later or an underscore(_) or a dolor sign ($). It can contain digits in the middle. Non of the following characters can be used while naming variables : 

       #%&"()'*+,:-./?<=>@[\]~!;{|}`.

   

   white spaces (space/ tab) are also note allowed in variable name.

   It must not be a keyword. It must not be a reserved word like "true", "false" and "null".

    It will be unique within the scope.

VARIABLES: If you create a program used to perform calculations as introduced above, when a user enters a new value that would be involved in the calculation, to manage that value, you can (temporarily) store it in the computer memory. Since the values entered in a reserved memory area change regularly, they are called variables. Because neither you nor the compiler can predict all possible values that would be used, there are safeguards you can use. First, you must ask the compiler to reserve an area of memory for a value you intend to use. Asking the compiler to reserve an area of memory is referred to as Declaring a Variable. Remember that when you declare a variable, the compiler reserves an area of the compiler memory for you.  

VARIABLE DECLARATION:        

           After declaring a variable, when you need the value stored in its memory area, you can ask the compiler to retrieve it and hand it to you. To effectively handle this transaction, the compiler would need two pieces of information from you: a name of your choice for the memory area that will be reserved, and the type of value that will be stored in that area of memory. Based on this, the formula to declare a variable is:

TypeOfValue VariableName

As done in some languages like Pascal or Basic, we will start with the name.

VARIABLE INITIALIZATION:

                After declaration of variables can be initialized in the following manner :

                  variable_name = value; 

       

      To initialize a variable, on the right side of its name, type the assignment operator, followed by the value you want to put in the reserved memory. As we will see in the next few sections, you cannot and should not put just any type of value in a variable. We will see that there are different types used for different variables.

Introduction To Data Types:

            when declaring a variable, besides its name, you must provide the type of information that the variable will hold. The role of this type is to tell the compiler how much memory will be needed to store the value(s) of that variable. Since your program is not the only one used in the computer, memory has to be effectively managed 

      The type of value that a variable will hold is called a data type. As you ay imagine, different variables can be meant to hold different types of values. Each data type uses a Java keyword to be characterized. As a modern language, Java provides even more support for its traditional data types. To do this, a class was created for each data type. This allows you to get more information from a variable declared with the particular data type you want to use. 
The Primitive Data Types Of Java:
        Java is strongly typed language, every variable must have a data type. Java has two forms of data types (1) Primitive (2) Reference. A primitive type of variable hold only a single value in memory. if we declare a variable to be of a specific primitive data type, that variable will always hold value of that data type.  
Java define 8 primitive data types. These can be put in four groups - Integer, Floating-point numbers, Characters and Boolean. Let us describes the groups one by one.

Integer Data Type: Integer can hold signed whole numbers like 123, -76 and 256. Signed whole numbers means positive(+ve) and negative(-ve) whole numbers. The size of the value which it can store depends on the integer data type we choose. Java support four types of integers, which are shown bellow.

Name                            Size                                Range

byte                               8 bits                            2