A variable is a container which holds the value while the Java program is executed. A variable is assigned with a data type.
Variable is a name of memory location. There are three types of variables in java: local, instance and static.
There are two types of data types in Java: primitive and non-primitive.

Table of Contents

Variable

Variable is name of reserved area allocated in memory. In other words, it is a name of memory location. It is a combination of “vary + able” that means its value can be changed.
1. int data=50;//Here data is variable

Types of Variables

There are three types of variables in Java:
• local variable
• instance variable
• static variable

1) Local Variable

A variable declared inside the body of the method is called local variable. You can use this variable only within that method and the other methods in the class aren’t even aware that the variable exists.
A local variable cannot be defined with “static” keyword.

2) Instance Variable

A variable declared inside the class but outside the body of the method, is called instance variable. It is not declared as static.
It is called instance variable because its value is instance specific and is not shared among instances.

3) Static variable

A variable which is declared as static is called static variable. It cannot be local. You can create a single copy of static variable and share among all the instances of the class. Memory allocation for static variable happens only once when the class is loaded in the memory.

Example to understand the types of variables in java

1. class A{ 
2. int data=50;//instance variable 
3. static int m=100;//static variable 
4. void method(){ 
5. int n=90;//local variable 
6. } 
7. }//end of class

Java Variable Example: Add Two Numbers

1. class Simple{ 
2. public static void main(String[] args){ 
3. int a=10; 
4. int b=10; 
5. int c=a+b; 
6. System.out.println(c); 
7. }}

Output:
20

Java Variable Example: Widening

1. class Simple{ 
2. public static void main(String[] args){ 
3. int a=10; 
4. float f=a; 
5. System.out.println(a); 
6. System.out.println(f); 
7. }}

Output:
10
10.0

Java Variable Example: Narrowing (Typecasting)

1. class Simple{ 
2. public static void main(String[] args){ 
3. float f=10.5f; 
4. //int a=f;//Compile time error 
5. int a=(int)f; 
6. System.out.println(f); 
7. System.out.println(a); 
8. }}

Output:
10.5
10

Java Variable Example: Overflow

1. class Simple{ 
2. public static void main(String[] args){ 
3. //Overflow 
4. int a=130; 
5. byte b=(byte)a; 
6. System.out.println(a); 
7. System.out.println(b); 
8. }}

Output:
130
-126

Java Variable Example: Adding Lower Type

1. class Simple{ 
2. public static void main(String[] args){ 
3. byte a=10; 
4. byte b=10; 
5. //byte c=a+b;//Compile Time Error: because a+b=20 will be int 
6. byte c=(byte)(a+b); 
7. System.out.println(c); 
8. }}

:
20

Unicode System

Unicode is a universal international standard character encoding that is capable of representing most of the world’s written languages.

Why java uses Unicode System?

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.

Problem

This caused two problems:
1. A particular code value corresponds to different letters in the various language standards.
2. The encodings for languages with large character sets have variable length.Some common characters are encoded as single bytes, other require two or more byte.

Solution

To solve these problems, a new language standard was developed i.e. Unicode System.

In unicode, character holds 2 byte, so java also uses 2 byte for characters.

lowest value:\u0000

highest value:\uFFFF

Java Keywords

Java keywords are also known as reserved words. Keywords are particular words which acts as a key to a code. These are predefined words by Java so it cannot be used as a variable or object name.
List of Java Keywords
A list of Java keywords or reserved words are given below:

1. abstract: Java abstract keyword is used to declare abstract class. Abstract class can provide the implementation of interface. It can have abstract and non-abstract methods.

2. boolean: Java boolean keyword is used to declare a variable as a boolean type. It can hold True and False values only.

3. break: Java break keyword is used to break loop or switch statement. It breaks the current flow of the program at specified condition.

4. byte: Java byte keyword is used to declare a variable that can hold an 8-bit data values.

5. case: Java case keyword is used to with the switch statements to mark blocks of text.

6. catch: Java catch keyword is used to catch the exceptions generated by try statements. It must be used after the try block only.

7. char: Java char keyword is used to declare a variable that can hold unsigned 16-bit Unicode characters

8. class: Java class keyword is used to declare a class.

9. continue: Java continue keyword is used to continue the loop. It continues the current flow of the program and skips the remaining code at the specified condition.

10. default: Java default keyword is used to specify the default block of code in a switch statement.

11. do: Java do keyword is used in control statement to declare a loop. It can iterate a part of the program several times.

12. double: Java double keyword is used to declare a variable that can hold a 64-bit floating-point numbers.

13. else: Java else keyword is used to indicate the alternative branches in an if statement.

14. enum: Java enum keyword is used to define a fixed set of constants. Enum constructors are always private or default.

15. extends: Java extends keyword is used to indicate that a class is derived from another class or interface.

16. final: Java final keyword is used to indicate that a variable holds a constant value. It is applied with a variable. It is used to restrict the user.

17. finally: Java finally keyword indicates a block of code in a try-catch structure. This block is always executed whether exception is handled or not.

18. float: Java float keyword is used to declare a variable that can hold a 32-bit floating-point number.

19. for: Java for keyword is used to start a for loop. It is used to execute a set of instructions/functions repeatedly when some conditions become true. If the number of iteration is fixed, it is recommended to use for loop.

20. if: Java if keyword tests the condition. It executes the if block if condition is true.

21. implements: Java implements keyword is used to implement an interface.

22. import: Java import keyword makes classes and interfaces available and accessible to the current source code.

23. instanceof: Java instanceof keyword is used to test whether the object is an instance of the specified class or implements an interface.

24. int: Java int keyword is used to declare a variable that can hold a 32-bit signed integer.

25. interface: Java interface keyword is used to declare an interface. It can have only abstract methods.

26. long: Java long keyword is used to declare a variable that can hold a 64-bit integer.

27. native: Java native keyword is used to specify that a method is implemented in native code using JNI (Java Native Interface).

28. new: Java new keyword is used to create new objects.

29. null: Java null keyword is used to indicate that a reference does not refer to anything. It removes the garbage value.

30. package: Java package keyword is used to declare a Java package that includes the classes.

31. private: Java private keyword is an access modifier. It is used to indicate that a method or variable may be accessed only in the class in which it is declared.

32. protected: Java protected keyword is an access modifier. It can be accessible within package and outside the package but through inheritance only. It can’t be applied on the class.

33. public: Java public keyword is an access modifier. It is used to indicate that an item is accessible anywhere. It has the widest scope among all other modifiers.

34. return: Java return keyword is used to return from a method when its execution is complete.

35. short: Java short keyword is used to declare a variable that can hold a 16-bit integer.

36. static: Java static keyword is used to indicate that a variable or method is a class method. The static keyword in Java is used for memory management mainly.

37. strictfp: Java strictfp is used to restrict the floating-point calculations to ensure portability.

38. super: Java super keyword is a reference variable that is used to refer parent class object. It can be used to invoke immediate parent class method.

39. switch: The Java switch keyword contains a switch statement that executes code based on test value. The switch statement tests the equality of a variable against multiple values.

40. synchronized: Java synchronized keyword is used to specify the critical sections or methods in multithreaded code.

41. this: Java this keyword can be used to refer the current object in a method or constructor.

42. throw: The Java throw keyword is used to explicitly throw an exception. The throw keyword is mainly used to throw custom exception. It is followed by an instance.

43. throws: The Java throws keyword is used to declare an exception. Checked exception can be propagated with throws.

44. transient: Java transient keyword is used in serialization. If you define any data member as transient, it will not be serialized.

45. try: Java try keyword is used to start a block of code that will be tested for exceptions. The try block must be followed by either catch or finally block.

46. void: Java void keyword is used to specify that a method does not have a return value.

47. volatile: Java volatile keyword is used to indicate that a variable may change asynchronously.

48. while: Java while keyword is used to start a while loop. This loop iterates a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop.

So, this brings us to the end of blog. This Tecklearn ‘Variables and Keywords in Java’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Java and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

Java and JEE Training

Java and JEE Training

About the Course

Java and JEE Certification Training is designed by professionals as per the industrial requirements and demands. This training encompasses comprehensive knowledge on basic and advanced concepts of core Java & J2EE along with popular frameworks like Hibernate, Spring & SOA. In this course, you will gain expertise in concepts like Java Array, Java OOPs, Java Function, Java Loops, Java Collections, Java Thread, Java Servlet, and Web Services using industry use-cases and this will help you to become a certified Java expert.

Why Should you take Java and JEE Training?

• Java developers are in great demand in the job market. With average pay going between $90,000/- to $120,000/- depending on your experience and the employers.
• Used by more than 10 Million developers worldwide to develop applications for 15 Billion devices.
• Java is one of the most popular programming languages in the software world. Rated #1 in TIOBE Popular programming languages index (15th Consecutive Year)

What you will Learn in this Course?

Introduction to Java

• Java Fundamentals
• Introduction to Java Basics
• Features of Java
• Various components of Java language
• Benefits of Java over other programming languages
• Key Benefits of Java

Installation and IDE’s for Java Programming Language

• Installation of Java
• Setting up of Eclipse IDE
• Components of Java Program
• Editors and IDEs used for Java Programming
• Writing a Simple Java Program

Data Handling and Functions

• Data types, Operations, Compilation process, Class files, Loops, Conditions
• Using Loop Constructs
• Arrays- Single Dimensional and Multi-Dimensional
• Functions
• Functions with Arguments

OOPS in Java: Concept of Object Orientation

• Object Oriented Programming in Java
• Implement classes and objects in Java
• Create Class Constructors
• Overload Constructors
• Inheritance
• Inherit Classes and create sub-classes
• Implement abstract classes and methods
• Use static keyword
• Implement Interfaces and use it

Polymorphism, Packages and String Handling

• Concept of Static and Run time Polymorphism
• Function Overloading
• String Handling –String Class
• Java Packages

Exception Handling and Multi-Threading

• Exception handling
• Various Types of Exception Handling
• Introduction to multi-threading in Java
• Extending the thread class
• Synchronizing the thread

File Handling in Java

• Input Output Streams
• Java.io Package
• File Handling in Java

Java Collections

• Wrapper Classes and Inner Classes: Integer, Character, Boolean, Float etc
• Applet Programs: How to write UI programs with Applet, Java.lang, Java.io, Java.util
• Collections: ArrayList, Vector, HashSet, TreeSet, HashMap, HashTable

Java Database Connectivity (JDBC)

• Introduction to SQL: Connect, Insert, Update, Delete, Select
• Introduction to JDBC and Architecture of JDBC
• Insert/Update/Delete/Select Operations using JDBC
• Batch Processing Transaction
• Management: Commit and Rollback

Java Enterprise Edition – Servlets

• Introduction to J2EE
• Client Server architecture
• URL, Port Number, Request, Response
• Need for servlets
• Servlet fundamentals
• Setting up a web project in Eclipse
• Configuring and running the web app with servlets
• GET and POST request in web application with demo
• Servlet lifecycle
• Servlets Continued
• Session tracking and filter
• Forward and include Servlet request dispatchers

Java Server Pages (JSP)

• Fundamentals of Java Server Page
• Writing a code using JSP
• The architecture of JSP
• JSP Continued
• JSP elements: Scriptlets, expressions, declaration
• JSP standard actions
• JSP directives
• Introduction to JavaBeans
• ServletConfig and ServletContext
• Servlet Chaining
• Cookies Management
• Session Management

Hibernate

• Introduction to Hibernate
• Introduction to ORM
• ORM features
• Hibernate as an ORM framework
• Hibernate features
• Setting up a project with Hibernate framework
• Basic APIs needed to do CRUD operations with Hibernate
• Hibernate Architecture

POJO (Plain Old Java Object)

• POJO (Plain Old Java Object)
• Persistent Objects
• Lifecycle of Persistent Object

Spring

• Introduction to Spring
• Spring Fundamentals
• Advanced Spring

Got a question for us? Please mention it in the comments section and we will get back to you.

319