Design (LLD) Blockchain - Machine Coding

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Low-level design (LLD) for a blockchain:

  1. Data structure: The blockchain will need to store the data that it is tracking, such as transactions or records. This will likely involve using a data structure such as a linked list or a tree to store the data in a sequential and tamper-evident manner.

  2. Consensus mechanism: The blockchain will need to ensure that all participants in the network agree on the state of the data. This will involve implementing a consensus mechanism such as proof of work or proof of stake to validate new data and reach agreement on the current state of the blockchain.

  3. Cryptographic hashes: The blockchain will need to use cryptographic hashes to secure the data and provide tamper-evident properties. This will involve using a cryptographic hash function such as SHA-256 to generate a unique hash for each block of data.

  4. P2P network: The blockchain will need to communicate with other nodes on the network in order to exchange data and reach consensus. This will involve implementing a peer-to-peer (P2P) network protocol to allow nodes to connect and communicate with each other.

  5. Block creation and validation: The blockchain will need to create new blocks of data and validate them using the consensus mechanism and cryptographic hashes. This will involve creating functions to generate new blocks, validate the data, and add the blocks to the chain.

  6. User interface: Finally, we will need to design the user interface for the blockchain, including any necessary views or tools for interacting with the data and monitoring the network. This will involve creating wireframes and mockups, as well as implementing the front-end code to bring the design to life.

Here is a possible low-level design (LLD) for Blockchain in Java:

public class Blockchain {
    private List<Block> blocks;
    private Set<Transaction> currentTransactions;
    private Set<Node> nodes;

    public Blockchain() {
        this.blocks = new ArrayList<>();
        this.currentTransactions = new HashSet<>();
        this.nodes = new HashSet<>();

        // create the Genesis block
        createBlock(0, "1", "Genesis block");

    public Block createBlock(int index, String previousHash, String data) {
        Block block = new Block(index, System.currentTimeMillis(), currentTransactions, previousHash);
        return block;

    public void addTransaction(Transaction transaction) {
        // validate the transaction
        if (!transaction.getSender().equals("0")) {
            // check if the sender has sufficient funds


    public Set<Node> getNodes() {
        return nodes;

    public void registerNode(String address) {
        Node node = new Node(address);

    public boolean validateChain() {
        // validate the integrity of the chain by checking the hashes of the blocks
public class Node {
    private String address;

    public Node(String address) {
        this.address = address;

    public String getAddress() {
        return address;
public class Block {
    private int index;
    private long timestamp;
    private List<Transaction> transactions;
    private String previousHash;
    private String hash;

    public Block(int index, long timestamp, List<Transaction> transactions, String previousHash) {
        this.index = index;
        this.timestamp = timestamp;
        this.transactions = transactions;
        this.previousHash = previousHash;
        this.hash = calculateHash();

    private String calculateHash() {
        // use cryptographic hash function to create a unique digital fingerprint for this block

    public int getIndex() {
        return index;

    public long getTimestamp() {
        return timestamp;

    public List<Transaction> getTransactions() {
        return transactions;

    public String getPreviousHash() {
        return previousHash;

    public String getHash() {
        return hash;
public class Transaction {
    private String sender;
    private String recipient;
    private double amount;

    public Transaction(String sender, String recipient, double amount) {
        this.sender = sender;
        this.recipient = recipient;
        this.amount = amount;

    public String getSender() {
        return sender;

    public String getRecipient() {
        return recipient;

    public double getAmount() {
        return amount;

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