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Java Programming Overview

Aug 25, 2025

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Overview

This lecture introduces Java programming, focusing on core concepts, object-oriented principles, data types, exception handling, file I/O, Java Collections, and XML/JSON processing.

Introduction to Java

  • Java is an object-oriented programming (OOP) language where everything is represented as objects with state and behavior.
  • Java was developed by Sun Microsystems in 1995, is open source, and currently maintained by Oracle.
  • Key features: simple syntax, high performance, secure (no pointers), robust, portable (write once, run anywhere), dynamic, distributed, and multi-threaded.
  • Widely used in Android apps, finance, web applications, embedded systems, scientific computing, big data, and IoT.

Java Setup and Internals

  • Install JDK specific to your OS; add it to the system PATH to run Java commands.
  • Use an IDE (Eclipse, IntelliJ) for code development.
  • Java source code (.java) is compiled to bytecode (.class), then executed by JVM.
  • JVM is platform-specific and enables Java’s platform independence.

Basic Java Concepts

  • Variables: Hold values; types include local (method scope), instance (object scope), static (class scope).
  • Data Types: Eight primitives (byte, short, int, long, float, double, char, boolean); non-primitives include String, arrays, and user-defined classes.
  • Type Conversion: Implicit (automatic), explicit (type casting).
  • Operators: Arithmetic, relational, logical, assignment, bitwise, unary, and ternary.

Control Statements and Methods

  • Control Statements: if, if-else, switch, for, while, do-while, break, continue, return.
  • Methods: Define class behavior, take parameters, may return values, improve code reuse and readability.
  • Method Overloading: Multiple methods with same name, different parameters.

Object-Oriented Programming

  • Class: Blueprint defining state (fields) and behavior (methods).
  • Object: Instance of a class.
  • Access Modifiers: public, private, protected, default—control visibility.
  • Constructor: Special method for object initialization; can be overloaded.
  • Inheritance: "is-a" relationship; enables method overriding and code reuse.
  • Polymorphism: Same interface, different implementations (overloading/overriding).
  • Abstraction: Hiding implementation details via abstract classes/interfaces.
  • Encapsulation: Bundling data/methods, restricting access using access modifiers.
  • Interfaces: 100% abstract; used for specifications and multiple inheritance.

Arrays, Strings, and Wrappers

  • Arrays: Fixed-size, same data type; single/multi-dimensional.
  • String: Immutable, widely used, supports many utility methods.
  • StringBuffer/StringBuilder: Mutable string variants for efficiency.
  • Wrapper Classes: Object representation of primitives (Integer, Double, etc.).

Exception Handling

  • Exceptions: Disrupt program flow; checked (compile-time) or unchecked (runtime).
  • Handling: try-catch-finally blocks; throw/throws for custom/error propagation.
  • Custom Exceptions: User-defined by extending Exception.

Java Collections Framework

  • List: Ordered, allows duplicates (ArrayList, LinkedList, Vector).
  • Set: Unordered, unique elements (HashSet, LinkedHashSet, TreeSet).
  • Queue: FIFO (PriorityQueue, ArrayDeque), supports typical queue operations.
  • Map: Key-value pairs, unique keys (HashMap, LinkedHashMap, TreeMap).
  • Generics: Type safety for collections.
  • Comparable/Comparator: Sorting mechanisms for user-defined classes.

File I/O and Serialization

  • Use java.io package for reading/writing files.
  • Stream-based I/O: InputStream/OutputStream for bytes, Reader/Writer for characters.
  • Serialization: Convert object state to byte stream for storage/sharing; use Serializable interface.

XML and JSON Processing

  • XML: Hierarchical, platform-independent data format; supports DTD/XSD schemas for validation.
  • XML Parsers: DOM (tree-based), SAX/StAX (event-based), XPath for querying.
  • JSON: Lightweight data exchange format using key-value pairs; preferred for web APIs.
  • Java supports reading/writing XML and JSON via external libraries (dom4j, JSON.simple, etc.).

Key Terms & Definitions

  • JVM — Java Virtual Machine; executes Java bytecode.
  • JDK — Java Development Kit; tools for Java development.
  • OOP — Object-Oriented Programming; paradigm centered on objects.
  • Polymorphism — Ability of methods to behave differently based on context.
  • Encapsulation — Restricting direct access to class internals.
  • Serialization — Converting objects to byte streams.
  • Collection — Data structure for storing groups of objects.

Action Items / Next Steps

  • Set up JDK and IDE (Eclipse/IntelliJ) on your machine.
  • Practice writing, compiling, and running basic Java programs.
  • Experiment with variables, methods, control statements, and OOP concepts.
  • Implement and manipulate data using Java Collections and arrays.
  • Write programs for file I/O and exception handling.
  • Read and write sample XML and JSON files using Java libraries.
  • Review these notes regularly and try coding exercises on each topic.

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