Java Variables and Data types

What is a variable?
Different definitions given below:

--Variable is a name of memory location
--A memory location to store temporary data within a   java program.
--A variable is a container which holds the value while the java program is executed. A variable is assigned with a datatype.
--It is a combination of "vary + able" that means its value can be changed.

Variable in Java
Variable Example
Types of Variables

1. Local variable -- used inside a method
Note: Local Variable contains garbage value
2. Instance/global variable --  used inside a class but outside method
Note: Global variable contain null or default value
3. Static variable -- We will discuss in separate post.

What is a Datatype?

--Data types specify the different sizes and values that can be stored in the variable. 
--A data type is a classification of the type of data that a variable or object can hold.
There are two types of data types in Java:
1. Primitive data types: The primitive data types include Boolean, char, byte, short, int, long, float and double.
2. Non-primitive data types: The non-primitive data types include String, Arrays, Classes and Interfaces.

Data types in Java

Data Type Hierarchy

Classification of Data Types

Classification of Data Types

Classification of Data Types

Why Java uses Unicode system?

Unicode is a universal international standard character encoding that is capable of representing most of the world's written languages. Before Unicode, there were many language standards:
ASCII (American Standard Code for Information Interchange) for the United States.
ISO 8859-1 for Western European Language.
KOI-8 for Russian.
GB18030 and BIG-5 for chinese, and so on.
So to support multinational application codes, some character was using single byte, some two. An even same code may represent a different character in one language and may represent other characters in another language.
To overcome above shortcoming, the unicode system was developed where each character is represented by 2 bytes.

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