Java Core Concepts — Algorithmic Library

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A structured, production-oriented reference library of 380+ Java programs spanning core language mechanics, classical algorithm design, advanced data structures, concurrency primitives, and applied number theory. Built as a living codebase — continuously expanded and categorized for engineering rigor.

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Table of Contents

• Repository Architecture
• Domain Taxonomy
  • I. Concurrency & Multithreading
  • II. Linear Data Structures & ADT Implementations
  • III. Sorting Algorithm Suite
  • IV. Multi-Dimensional Matrix Logic
  • V. Advanced Array Manipulation & Search
  • VI. Object-Oriented Architecture & Design Patterns
  • VII. Exception Handling & Defensive Programming
  • VIII. String Processing & Lexical Analysis
  • IX. Number Theory & Computational Mathematics
  • X. Mathematical Series & Sequence Generation
  • XI. Cryptographic Encoding & Cipher Logic
  • XII. Pattern Synthesis & Geometric Rendering
  • XIII. Domain-Modeled Business Logic
• Local Execution Guide
• Project Structure
• Author

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Repository Architecture

Java-Core-Concepts/
└── Programs/
    ├── *.java          # Source files (380+)
    ├── *.class         # Compiled bytecode
    └── *.ctxt          # BlueJ context metadata

All programs are self-contained, single-responsibility units. Each file compiles and runs independently with no external dependencies beyond the Java Standard Library.

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Domain Taxonomy

I. Concurrency & Multithreading

Implementations of core Java concurrency primitives — thread lifecycle management, monitor-based synchronization, and the classic Producer-Consumer coordination pattern using wait()/notifyAll().

File	Concept
ProducerConsumer.java	Bounded-buffer Producer-Consumer using synchronized, wait(), notifyAll()
ThreadSynchronization.java	Monitor-based mutual exclusion with synchronized methods on a shared resource
ATMWithdrawal.java	Race condition prevention in concurrent bank withdrawal simulation
CounterThread.java	Thread lifecycle and atomic counter management

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II. Linear Data Structures & ADT Implementations

Hand-rolled implementations of foundational Abstract Data Types — no java.util scaffolding. Demonstrates deep understanding of pointer manipulation, memory layout, and interface contracts.

File	Concept
Stack.java	Array-backed generic Stack with overflow/underflow guards, push/pop/display
Node.java	Singly Linked List with dynamic node insertion, traversal, salary-update mutation, and targeted deletion
IntegerList.java	Integer list ADT with custom iteration logic

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III. Sorting Algorithm Suite

A comprehensive suite of classical and non-classical sorting algorithms implemented from first principles — no library sort calls.

File	Algorithm	Complexity
Sort_bubble.java	Bubble Sort	O(n²)
Selection_array.java / Selection_array2.java	Selection Sort	O(n²)
Selection_ascend.java / Selection_descend.java	Bidirectional Selection Sort	O(n²)
Pendulum_sort.java	Pendulum Sort (oscillating placement)	O(n²)
Circular_sort.java / Circular_sort2.java	Circular Sort	O(n²)
Arraymid_sort.java	Mid-pivot Sort	O(n²)
Sort_ascend.java / Sort_descend.java	Comparative Sort variants	O(n²)
Sort_percent.java	Percentage-weighted Sort	O(n²)
Sort_student.java / Selection_student.java	Object-keyed Sort (student records)	O(n²)
Matrix_sort.java	Row-wise Matrix Sort	O(n² log n)
Ar2D_rowsort.java / Ar2D_columnsort.java / Ar2D_fullsort.java	2D Matrix Sort variants	O(n² log n)

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IV. Multi-Dimensional Matrix Logic

Advanced 2D matrix operations covering geometric transformations, traversal algorithms, and structural analysis — the kind of problems that appear in technical screening rounds.

File	Operation
Ar2D_spiralmatrix.java	Spiral-order matrix population (layer-by-layer boundary traversal)
Ar2D_rotate.java / Ar2D_rotate270.java / Ar2D_rotatefull.java	In-place matrix rotation (90°, 270°, 360°)
Ar2D_transpose.java	Matrix transposition
Ar2D_magicsquare.java / MagicSquare.java	Magic square generation and validation
Ar2D_symmetry.java	Symmetric matrix detection
Ar2D_prdiagonal.java / Ar2D_sqdiagonal.java	Principal and secondary diagonal extraction
Ar2D_zigzagtrix.java	Zigzag traversal pattern
Ar2D_trianmatrix.java	Triangular matrix operations
Ar2D_rowshift.java	Circular row-shift transformation
Ar2D_rowmaxmin.java	Row-wise max/min extraction
Ar2D_nextprimetrix.java	Element-wise next-prime substitution
Ar2D_matrange.java	Range-bounded matrix filtering
Ar2D_addmatrix.java / Ar2D_subtmatrix.java / Ar2D_multmatrix.java	Matrix arithmetic operations
Ar2D_colsum.java / Ar2D_sum.java	Column-sum and total-sum aggregation
Ar2D_squarem.java / Sq_matrix.java	Square matrix validation and operations
EqMat.java	Matrix equality comparison
Matrix_case.java	Case-driven matrix operation dispatcher

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V. Advanced Array Manipulation & Search

Single-dimensional array algorithms covering frequency analysis, set operations, structural rearrangement, and search strategies.

File	Concept
Linear_search.java	Linear search with boundary validation
Binary.java	Binary search on sorted arrays
Arr_common.java / Arr_union.java	Set intersection and union on integer arrays
Duplicate.java / Duplicate_remove.java	Duplicate detection and in-place removal
Ar_frequency.java / Freq.java	Element frequency mapping
Ar_maxfreq.java	Maximum frequency element extraction
Arrfrequency_prime.java	Frequency-filtered prime extraction
Array_rearrange.java	Conditional element rearrangement
Ar_posnegative.java	Positive/negative partition
Ar_oddindex.java	Odd-index element extraction
Ar_bound.java / Ar_Boundary.java	Boundary element traversal
Lucky_array.java / Lucky_array2.java	Lucky number sieve on arrays
Ar_sd.java	Standard deviation computation
Ar_roundvalue.java	Rounding and precision normalization
Ar_tripdig.java	Triple-digit element filtering
Ar_identical.java	Array identity comparison
Remove_element.java	Targeted element removal with shift
Largest_Set.java	Maximum subset identification
Prodmaxodd.java	Product of maximum odd elements
Productsmall.java	Product of smallest elements
CompX_ar1.java / CompX_ar2.java	Comparative array analysis
Exp_Ar_enhanced_loop.java	Enhanced for-loop array traversal patterns
Array_mobile.java	Mobile-number array validation

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VI. Object-Oriented Architecture & Design Patterns

Programs demonstrating core OOP pillars — encapsulation, inheritance, polymorphism, and interface-driven design — applied to real-world domain models.

File	Concept
Shape.java	Interface-based polymorphic shape hierarchy
Employee.java	Encapsulated employee entity with accessor/mutator contracts
Bowler.java	Inheritance-based sports domain model
Calculator.java / Modifiedcalculator.java	Stateful calculator with method overloading
Switchcalculator.java	Switch-dispatch arithmetic engine
Area_overload.java / HCFOverload.java / PatOverload.java	Method overloading across geometric and numeric domains
Box_capacity.java	Volumetric capacity model with constructor chaining
Date.java / TimeAdd.java	Temporal domain objects with validation logic
Login.java / Security.java	Credential validation and access control simulation
Coin.java	Denomination-based currency model
Tax.java / Ebill.java / telebill.java	Tax and billing computation models
Telephone.java	Telecom billing domain object
Marks_average.java / Points_avg.java	Academic scoring aggregation
ClsStr1.java / ClsStr2.java	String-class composition patterns
InputProcessor.java	Generic input processing abstraction
EventListenerDemo.java	Observer/event-listener pattern demonstration
MyGuiExample.java	AWT/Swing GUI component integration

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VII. Exception Handling & Defensive Programming

Custom exception hierarchies and multi-catch patterns demonstrating production-grade error boundary design.

File	Concept
HrsException.java	Multi-exception hierarchy (HrsException, MinException, SecException) with domain-validated Time object
ArrayIndexOutOfBoundsException.java	Bounds-check exception handling and recovery
ATMWithdrawal.java	InterruptedException handling in concurrent context

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VIII. String Processing & Lexical Analysis

A deep suite of string manipulation algorithms covering lexical transformations, cipher operations, and linguistic analysis.

File	Concept
Str_anagram.java	Anagram detection via character frequency matching
Str_magic.java	Magic string detection
Str_encode.java / Str_encodeshift.java	Character-shift encoding schemes
Str_rotate.java / Str_rotation.java	String rotation and rotation-equivalence check
Str_sentsort.java	Word-level sentence sorting
Str_wordformat.java	Word capitalization and formatting normalization
Str_letcombination.java	Letter permutation and combination generation
Str_numbtorom.java	Integer to Roman numeral conversion
Str_numbtoword.java	Integer to English word-form conversion
Str_wordpercent.java	Word-type percentage analysis
Str_occurvowel.java / Str_vowel.java	Vowel occurrence and frequency analysis
Str_novowel.java	Vowel-stripped string transformation
Str_evenchar.java	Even-indexed character extraction
Str_interchange.java	Character-position interchange
Str_midelete.java	Mid-character deletion
Str_merge.java	Sorted string merge
Str_swap.java	Word-pair swap transformation
Str_ascii.java	ASCII value mapping and analysis
Str_blank.java	Whitespace normalization
Str_constr.java	String construction from character constraints
Str_convert.java	Case and format conversion
Str_count.java	Character and word count analysis
Str_notadd.java	Numeric-string concatenation guard
Str_ocurrence.java	Substring occurrence counting
Str_print.java	Formatted string output patterns
Str_test.java / Str_test2.java	String method exploration
Str_letter.java	Letter classification and extraction
String_check.java	Multi-condition string validation
String_doubleseq.java	Double-character sequence detection
String_length.java	Length-based string operations
StringModify.java	In-place string modification patterns
Reverse_string.java	String and word-level reversal
Psentence.java	Sentence parsing and reconstruction
Sentence.java	Sentence-level lexical operations
Word_number.java	Word-to-number mapping
Encrypt.java / Encrypt_Main.java / Encryptg.java	Vowel-consonant segregation cipher with bubble-sort ordering

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IX. Number Theory & Computational Mathematics

Implementations of classical number-theoretic predicates and special integer classifications — a direct signal of algorithmic depth to any technical interviewer.

File	Number Class
Kaprekar.java	Kaprekar numbers (range-based detection via digit-split squaring)
Automorphic.java	Automorphic number detection
FascinatingNumber.java	Fascinating number validation
SpecialPureNumber.java	Special pure number classification
Neon.java	Neon number detection (digit-sum of square equals original)
Ugly_number.java	Ugly number sequence (prime factors limited to 2, 3, 5)
Adam_integer.java	Adam integer (reversals of square are squares of reversal)
Abundant.java	Abundant number detection (sum of proper divisors > n)
Amstrong.java	Armstrong/Narcissistic number detection
Palindrome.java / Palindrome1.java / Palinrange.java	Palindrome detection and range enumeration
FiboPrime.java	Fibonacci-prime intersection
NonFibo.java	Non-Fibonacci number identification
Octaprime.java	Octal-prime classification
Seprime.java	Self-prime number detection
Digit_prime.java	Digit-sum prime validation
Digcomposite.java	Digit-composite classification
ISprime.java	Primality test
Nextprime.java	Next prime computation
Sunny.java	Sunny number detection
Pell_number.java	Pell sequence generation (P(n) = 2·P(n-1) + P(n-2))
PC_digit.java	Digit-based prime/composite analysis
DDigit_prog.java / Digit_prog.java	Digit manipulation programs
Digit_sum.java	Iterative digit sum reduction
Multiply_digits.java	Digit product computation
Takingdigits.java	Digit extraction and reconstruction
Digt_num.java	Digit-count operations
LCM.java / Lcm3.java	LCM computation (2-variable and 3-variable)
Compnumber.java	Composite number classification
Leapyear.java	Gregorian leap year validation
Quadratic.java	Quadratic equation root solver (real and complex)
Binodd.java	Binomial odd-term analysis

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X. Mathematical Series & Sequence Generation

Iterative and recursive series generation covering classical sequences and custom recurrence relations.

File	Series
Fibonacciseries.java	Fibonacci sequence
Pell_number.java	Pell sequence
SeriesSum.java / SeriesSum1.java	Summation series (various formulas)
Series.java / Series2.java	Custom recurrence series
Sumseries.java	Cumulative sum series
Menu_series.java	Menu-driven multi-series dispatcher
Sumproduct.java / Sumproduct2.java	Sum-product hybrid series
Half_ascdesc.java	Ascending-descending half-series
Counting.java	Counting sequence generation
RecursionOutputs.java	Recursive call-stack output tracing

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XI. Cryptographic Encoding & Cipher Logic

Character-level encoding and transformation algorithms demonstrating applied string manipulation under constraint.

File	Cipher Type
Encrypt.java	Vowel-consonant segregation cipher with sorted-vowel prefix encoding
Str_encode.java	Positional character shift encoding
Str_encodeshift.java	Shift-cipher with configurable offset
TWIST.java	Character-twist transformation
Dec_to_hex.java / ToHex.java	Decimal-to-hexadecimal base conversion
Dec_to_Oct.java / DeciOct.java	Decimal-to-octal base conversion
Hextodec.java	Hexadecimal-to-decimal conversion
charcon.java	Character encoding conversion

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XII. Pattern Synthesis & Geometric Rendering

Nested-loop pattern generation — a deceptively deep domain for testing loop invariant reasoning and off-by-one precision.

File	Pattern Type
Pattern.java / Pattern1.java / Pattern2.java / Pattern3.java / Pattern4.java	Numeric and symbolic grid patterns
PatternA.java / Patternx.java	Alphabetic and cross patterns
Patter1.java	Inverted triangle patterns
Pat.java / Pat_tr.java	Triangle and pyramid patterns
CharRectangle.java	Character-filled rectangle rendering
Striangle.java	Star-triangle pattern
pate1hw.java / Pate2hw.java	Homework-grade pattern exercises

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XIII. Domain-Modeled Business Logic

Object-oriented programs modeling real-world business domains — demonstrates ability to translate requirements into class hierarchies.

File	Domain
ATMWithdrawal.java	Concurrent ATM transaction simulation
Ebill.java	Electricity billing with slab-rate computation
telebill.java	Telecom billing with call-rate tiers
Tax.java	Income tax computation with bracket logic
Telephone.java	Telephone directory and billing model
Login.java / Security.java	Authentication and access control
Bowler.java	Cricket bowler performance analytics
Array_mobile.java	Mobile number validation and storage
Travprog.java	Travel program cost computation
PipesProblem.java	Pipes-and-cisterns rate problem solver
Schoolprograms.java	School management domain model
Menew.java / Menu.java	Menu-driven application dispatcher

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Local Execution Guide

Prerequisites: JDK 8+ installed and javac/java on your PATH.

Compile a single program

cd Java-Core-Concepts/Programs

javac FileName.java

Run the compiled bytecode

java FileName

Example — run the Spiral Matrix program

cd Java-Core-Concepts/Programs

javac Ar2D_spiralmatrix.java
java Ar2D_spiralmatrix

Example — run the Producer-Consumer concurrency demo

cd Java-Core-Concepts/Programs

javac ProducerConsumer.java
java ProducerConsumer

Example — run the Kaprekar number range finder

cd Java-Core-Concepts/Programs

javac Kaprekar.java Kaprekar_main.java
java Kaprekar_main

Note: Programs with a _main suffix (e.g., Kaprekar_main.java) contain the main() entry point and depend on their paired class file. Compile both together as shown above.

Compile all programs at once

cd Java-Core-Concepts/Programs

javac *.java

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Project Structure

Java-Core-Concepts/
├── README.md
└── Programs/
    ├── Concurrency          → ProducerConsumer, ThreadSynchronization, ATMWithdrawal, CounterThread
    ├── Data Structures      → Stack, Node (Linked List), IntegerList
    ├── Sorting Algorithms   → Bubble, Selection, Pendulum, Circular, Matrix sorts
    ├── 2D Matrix Logic      → Spiral, Rotate, Transpose, Magic Square, Zigzag, Diagonal
    ├── Array Algorithms     → Search, Set ops, Frequency, Rearrangement, Lucky sieve
    ├── OOP & Design         → Employee, Shape, Calculator, Date, Login, EventListener
    ├── Exception Handling   → HrsException hierarchy, ArrayIndexOutOfBounds
    ├── String Processing    → Anagram, Cipher, Rotation, Roman numerals, Word conversion
    ├── Number Theory        → Kaprekar, Automorphic, Neon, Ugly, Armstrong, Pell, FiboPrime
    ├── Series Generation    → Fibonacci, Pell, Custom recurrence, SeriesSum
    ├── Encoding & Ciphers   → Encrypt, Shift cipher, Base conversion (Hex, Octal)
    ├── Pattern Rendering    → Triangle, Pyramid, Grid, Alphabetic patterns
    └── Business Logic       → ATM, Billing, Tax, Authentication, Sports analytics

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Author

Sayan — 3rd Year B.Tech, Computer Science Engineering

Actively building toward a career in enterprise software engineering. This repository is a living reference — programs are continuously added, refactored, and categorized as new concepts are mastered.

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_{Built with Java SE · Compiled with javac · No external dependencies}