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 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 Type Hierarchy

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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