Java – The Complete Reference

By / Programming eBook

Java – The Complete Reference

1. Introduction to Java

Java is a high-level, object-oriented, class-based programming language developed by Sun Microsystems in 1995 (now owned by Oracle). It is designed to be platform-independent, secure, robust, and portable.

Java follows the principle:

“Write Once, Run Anywhere (WORA)”

Java is widely used for:

  • Desktop applications
  • Web applications
  • Mobile apps (Android)
  • Enterprise systems
  • Cloud & distributed systems

2. Features of Java

Key features that make Java powerful:

  • Platform Independent
  • Object-Oriented
  • Secure
  • Robust
  • Multithreaded
  • Portable
  • High Performance
  • Distributed
  • Dynamic

3. Java Platform Architecture

Java platform consists of three major components:

(a) JVM (Java Virtual Machine)

  • Converts bytecode into machine code
  • Makes Java platform independent
  • Manages memory and garbage collection

(b) JRE (Java Runtime Environment)

  • JVM + core libraries
  • Required to run Java programs

(c) JDK (Java Development Kit)

  • JRE + development tools (javac, java, debugger)
  • Required to develop Java applications

4. Java Program Structure

Basic structure of a Java program:

class HelloWorld { public static void main(String[] args) { System.out.println(“Hello, Java!”); } }

Main components:

  • Class definition
  • main() method
  • Statements
  • Comments

5. Data Types in Java

Java has two types of data types:

(a) Primitive Data Types

  • byte
  • short
  • int
  • long
  • float
  • double
  • char
  • boolean

(b) Non-Primitive Data Types

  • String
  • Array
  • Class
  • Interface

6. Variables in Java

Types of variables:

  1. Local Variable
  2. Instance Variable
  3. Static Variable

7. Operators in Java

Java supports various operators:

  • Arithmetic (+ - * / %)
  • Relational (< > <= >= == !=)
  • Logical (&& || !)
  • Assignment (= += -=)
  • Unary (++ --)
  • Bitwise (& | ^)

8. Control Statements

Used to control the flow of execution.

(a) Decision Making

  • if
  • if–else
  • switch

(b) Looping Statements

  • for
  • while
  • do-while

(c) Jump Statements

  • break
  • continue
  • return

9. Object-Oriented Programming (OOP) Concepts

Java is a pure object-oriented language (almost).

Core OOP Concepts:

  1. Class – Blueprint of objects
  2. Object – Instance of a class
  3. Encapsulation – Data hiding using private variables
  4. Inheritance – Acquiring properties of parent class
  5. Polymorphism – One name, many forms
  6. Abstraction – Hiding implementation details

10. Constructors

Constructors are special methods used to initialize objects.

Types:

  • Default constructor
  • Parameterized constructor

Rules:

  • Same name as class
  • No return type

11. Inheritance in Java

Types of inheritance supported:

  • Single
  • Multilevel
  • Hierarchical

(Java does not support multiple inheritance using classes, but supports it using interfaces.)

12. Polymorphism

Types:

  • Compile-time (Method Overloading)
  • Run-time (Method Overriding)

13. Abstraction

Achieved using:

  • Abstract classes
  • Interfaces

14. Packages in Java

Packages are used to:

  • Group related classes
  • Avoid name conflicts
  • Provide access protection

Types:

  • Built-in packages (java.lang, java.util)
  • User-defined packages

15. Exception Handling

Exception handling manages runtime errors.

Keywords:

  • try
  • catch
  • finally
  • throw
  • throws

Common exceptions:

  • ArithmeticException
  • NullPointerException
  • ArrayIndexOutOfBoundsException

16. Multithreading

Multithreading allows multiple threads to run simultaneously.

Benefits:

  • Efficient CPU utilization
  • Faster execution
  • Better responsiveness

Thread creation:

  • Extending Thread class
  • Implementing Runnable interface

17. File Handling

Java provides file handling through:

  • File class
  • FileInputStream
  • FileOutputStream
  • BufferedReader / BufferedWriter

18. Java Collections Framework

Used to store and manipulate data.

Main interfaces:

  • List
  • Set
  • Queue
  • Map

Popular classes:

  • ArrayList
  • LinkedList
  • HashSet
  • HashMap

19. Java Input/Output (I/O)

Java I/O is used to read and write data.

Types:

  • Byte stream
  • Character stream

20. Java Database Connectivity (JDBC)

JDBC allows Java programs to interact with databases.

Steps:

  1. Load driver
  2. Establish connection
  3. Create statement
  4. Execute query
  5. Close connection

21. Java Networking

Java supports networking using:

  • Socket
  • ServerSocket
  • URL

Used in:

  • Chat apps
  • Client-server applications

22. Java Security

Java provides security through:

  • Bytecode verification
  • Security Manager
  • Encryption APIs

23. Applications of Java

Java is used in:

  • Web applications
  • Mobile apps (Android)
  • Banking software
  • Enterprise systems
  • Cloud platforms

24. Advantages of Java

  • Platform independent
  • Secure and robust
  • Scalable
  • Large community support
  • Widely used in industry

Conclusion

Java is a powerful, versatile, and widely used programming language. From beginner-level programming to enterprise-grade applications, Java provides all necessary tools and technologies. Learning Java builds a strong foundation for software development and backend engineering.

Scroll to Top