Block.java

import java.util.Date;
import bslCoin.StringUtil;
import java.util.ArrayList;

public class Block {

    public String hash;
    public String previousHash;
    public String merkleRoot;
    public ArrayList<Transaction> transactions = new ArrayList<Transaction>(); // our data will be a simple message
    public long timeStamp; // as number of milliseconds since 1/1/2018.
    public int nonce;

    // Block Constructor
    public Block(String previousHash) {
        this.previousHash = previousHash;
        this.timeStamp = new Date().getTime();
        this.hash = calculateHash(); // Making sure we do this after we set the other values.
    }

    // Calculate new hash based on blocks contents
    public String calculateHash() {
        String calculatedhash = StringUtil
                .applySha256(previousHash + Long.toString(timeStamp) + Integer.toString(nonce) + merkleRoot);
        return calculatedhash;
    }

    //Increases nonce value until hash target is reached
    public void mineBlock(int difficulty) {
        merkleRoot = StringUtil.getMerkleRoot(transactions);
        String target = StringUtil.getDifficultyString(difficulty); // Create a string with difficulty * "0"
        while (!hash.substring(0, difficulty).equals(target)) {
            nonce++;
            hash = calculateHash();
        }
        System.out.println("Block Mined!!!: " + hash);
    }
    
    //Add transactions to this block
    public boolean addTransaction(Transaction transaction) {
        // process transaction and check if valid, unless block is genesis block then ignore
        if (transaction == null) return false;
        if((!"0".equals(previousHash))) {
            if((transaction.processTransaction() != true)) {
                System.out.println("Transaction failed to process. Discarded");
                return false;
            }
        }
        
        transactions.add(transaction);
        System.out.println("Transaction Successfully added to Block");
        return true;
        
    }

}