Collections From Scratch

This project explores Data Structures and Collections in Java by implementing them from scratch, without using the Java Collections Framework (JCF).

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Overview

This repository contains implementations of common data structures such as lists, sets, maps, stacks, queues, heaps, and trees. Each data structure is built from first principles, including custom iterators and benchmarking utilities to compare performance. Performance comparison utilities that benchmark custom data structures against Java's built-in counterparts (e.g., PriorityQueue for heaps, TreeSet for binary trees) using shuffled datasets to ensure fair testing.

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Features

• Core abstractions (CustomCollection, CustomIterator)
• Array-based and linked implementations (CustomArrayList, CustomLinkedList)
• Hash-based Collections (CustomHashSet, CustomHashMap)
• Stack, Queue, and Deque implementations (CustomStack, CustomQueue, CustomDeque)
• Tree structures (CustomBinaryTree)
• Heap implementations (CustomHeapList)
• Benchmarking utilities (Benchmark.java)

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Project Structure

src/main/java/com/brendanddev/collections
│
├── core/ # Shared interfaces & iterators
│ ├── CustomCollection.java
│ └── CustomIterator.java
│
├── list/ # Linear data structures
│ ├── CustomArrayList.java
│ └── CustomLinkedList.java
│
├── set/ # Unique element collections
│ └── CustomHashSet.java
│
├── map/ # Key-Value structures
│ └── CustomHashMap.java
│
├── queue/ # FIFO & Priority queues
│ ├── CustomQueue.java
│ ├── CustomDeque.java
│ └── CustomLinkedPriorityQueue.java
│
├── stack/ # LIFO structure
│ └── CustomStack.java
│
├── heap/ # Binary heap implementations
│ ├── CustomHeap.java
│ └── CustomHeapList.java
│
├── tree/ # Hierarchical structures
│ └── CustomBinaryTree.java
│
├── performance/    # Benchmarking utilities
│   ├── Benchmark.java
│   ├── CompareLists.java
│   ├── CompareQueues.java
│   ├── CompareStack.java
│   ├── CompareHeaps.java
│   ├── CompareMaps.java
│   ├── CompareSets.java
│   └── CompareTrees.java
│
└── Main.java # Entry point for demos/benchmarks

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Usage

Running the Demos

You can run the Main class to see basic demos of your custom collections in action:

mvn compile exec:java -Dexec.mainClass="com.brendanddev.collections.Main"

This will compile the project and run the main entry point. You can modify Main.java to call any custom collection and test basic operations.

Running Benchmarks

The performance package contains benchmarking utilities to compare your custom implementations with standard Java collections. Each Compare*.java class runs performance tests for a specific data structure.