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Java Core Concepts — Algorithmic Library

Java Algorithms Data Structures Concurrency OOP Programs License

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.

Table of Contents

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.

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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.

GitHub

Built with Java SE · Compiled with javac · No external dependencies