Block.java

package blockchain;

import java.util.ArrayList;
import java.util.Date;

public class Block {

	public String hash;
	public String previousHash;
	public String merkleRoot;
	public ArrayList<Transaction> transactions = new ArrayList<Transaction>();
	private long timeStamp; 
	private int nonce;

	//Block Constructor.
	public Block(String previousHash ) {
		this.previousHash = previousHash;
		this.timeStamp = new Date().getTime();
		this.hash = calculateHash(); 
	}
	
	public String calculateHash() {
		String calculatedhash = StringUtil.applySha256( 
				previousHash +
				Long.toString(timeStamp) +
				Integer.toString(nonce) + merkleRoot);
		return calculatedhash;
	}
	
	public void mineBlock(int difficulty) {
		merkleRoot = StringUtil.getMerkleRoot(transactions);
		String target = new String(new char[difficulty]).replace('\0', '0'); 
		while(!hash.substring( 0, difficulty).equals(target)) {
			nonce ++;
			hash = calculateHash();
		}
		System.out.println("Block Mined!!! : " + hash);
	}

	public boolean addTransaction(Transaction transaction) {
		// Unless block is Genesis block, process transaction and check if valid
		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;
	}

	
}