🧱 Blockchain Simulation in Java (with Singly Linked Lists)

This project is a basic simulation of a blockchain developed in Java using singly linked lists. It allows performing CRUD-S operations (Create, Read, Update, Delete, and Search) on the chain’s blocks, helping to understand the fundamentals of a dynamic data structure that simulates a blockchain network.

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👨‍💻 Authors

• Dago David Palmera Navarro

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📁 Project Structure

BlockchainSimulation/
├── src/
│   ├── app/
│   │   └── App.java
│   └── blockchain/
│       ├── Bloque.java
│       └── Blockchain.java
├── README.md

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🧠 Concept

A blockchain is a data structure where each block contains a set of data, an identifier, and the hash of the previous block. In this simulation, we use a singly linked list, where each node represents a block in the chain.

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⚙️ Features

• 📦 Add Blocks: Inserts new blocks with custom data.
• 🔍 Search Blocks: Allows searching for a block by its hash.
• 📋 Display Full Chain: Shows all existing blocks.
• ✏️ Update Block Data: Modifies the data of an existing block and updates its hashes.
• ❌ Delete a Block: Deletes a block by its ID, reorganizing the chain and recalculating hashes.

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🚀 Run Instructions

✅ Requirements

• JDK 17 or higher
• VSCode (recommended with Java Extension Pack)

🛠️ Compile and Run from Terminal

cd src
javac app/App.java
java app.App

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💻 Run from VSCode

1. Open the project folder in VSCode.

2. Open the App.java file.

3. Click on the Run button (▶️) or press F5.

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🧩 Class Descriptions

Block.java

Represents an individual block.

Attributes:

• int blockId
• String transactionData
• int previousHash
• int currentHash
• Bloque nextBlock

Key Methods:

• calculateHash(): Simulates a hash using Objects.hash( blockId, transactionData, previousHash);
• displayBlockInfo(): prints the block’s data

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Blockchain.java

Contains the logic of the linked list simulating the blockchain.

Attributes:

Main Methods:

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App.java

Main class with the main() method that tests the blockchain functionality.

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📌 Example Output

Full Blockchain:
Block 1:
Data: Alice sends 10 BTC to Bob
Previous hash: None
Current hash: 2125378565

Block 2:
Data: Bob sends 5 BTC to Charlie
Previous hash: 2125378565
Current hash: 2125378566

...

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📥 Possible Future Improvements

• Implementation of a real hashing algorithm (e.g., SHA-256)
• Blockchain integrity validation
• Graphical interface or REST API
• Persistent storage in files or database

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📘 Subject

Data Structures – Simulation of linked lists and dynamic structures applied to blockchain.

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