Made hash and previousHash variables private and added the correspond…

src/noobchain/Block.java

@@ -4,8 +4,8 @@
 
 public class Block {
 
-	public String hash;
-	public String previousHash; 
+	private String hash;
+    private String previousHash;
 	private String data; //our data will be a simple message.
 	private long timeStamp; //as number of milliseconds since 1/1/1970.
 	private int nonce;
@@ -15,13 +15,22 @@ public Block(String data,String previousHash ) {
 		this.data = data;
 		this.previousHash = previousHash;
 		this.timeStamp = new Date().getTime();
-
-		this.hash = calculateHash(); //Making sure we do this after we set the other values.
+
+        //Making sure we do this after we set the other values.
+		this.hash = calculateHash();
 	}
-
-	//Calculate new hash based on blocks contents
+
+    public String getHash() {
+        return hash;
+    }
+
+    public String getPreviousHash() {
+        return previousHash;
+    }
+
+    //Calculate new hash based on blocks contents
 	public String calculateHash() {
-		String calculatedhash = StringUtil.applySha256( 
+		String calculatedhash = StringUtil.applySha256(
 				previousHash +
 				Long.toString(timeStamp) +
 				Integer.toString(nonce) + 
@@ -32,8 +41,9 @@ public String calculateHash() {
 
 	//Increases nonce value until hash target is reached.
 	public void mineBlock(int difficulty) {
-		String target = StringUtil.getDificultyString(difficulty); //Create a string with difficulty * "0" 
-		while(!hash.substring( 0, difficulty).equals(target)) {
+        //Create a string with difficulty * "0"
+	    String target = StringUtil.getDificultyString(difficulty);
+		while (!hash.substring( 0, difficulty).equals(target)) {
 			nonce ++;
 			hash = calculateHash();
 		}

src/noobchain/NoobChain.java

@@ -1,6 +1,5 @@
 package noobchain;
 import java.util.ArrayList;
-import com.google.gson.GsonBuilder;
 
 public class NoobChain {
 
@@ -14,10 +13,10 @@ public static void main(String[] args) {
 		addBlock(new Block("Hi im the first block", "0"));
 
 		System.out.println("Trying to Mine block 2... ");
-		addBlock(new Block("Yo im the second block",blockchain.get(blockchain.size()-1).hash));
+		addBlock(new Block("Yo im the second block", blockchain.get(blockchain.size()-1).getHash()));
 
 		System.out.println("Trying to Mine block 3... ");
-		addBlock(new Block("Hey im the third block",blockchain.get(blockchain.size()-1).hash));	
+		addBlock(new Block("Hey im the third block", blockchain.get(blockchain.size()-1).getHash()));
 
 		System.out.println("\nBlockchain is Valid: " + isChainValid());
 
@@ -32,25 +31,27 @@ public static Boolean isChainValid() {
 		String hashTarget = new String(new char[difficulty]).replace('\0', '0');
 
 		//loop through blockchain to check hashes:
-		for(int i=1; i < blockchain.size(); i++) {
+		for (int i=1; i < blockchain.size(); i++) {
 			currentBlock = blockchain.get(i);
 			previousBlock = blockchain.get(i-1);
+
 			//compare registered hash and calculated hash:
-			if(!currentBlock.hash.equals(currentBlock.calculateHash()) ){
+			if (!currentBlock.getHash().equals(currentBlock.calculateHash())) {
 				System.out.println("Current Hashes not equal");			
 				return false;
 			}
+
 			//compare previous hash and registered previous hash
-			if(!previousBlock.hash.equals(currentBlock.previousHash) ) {
+			if (!previousBlock.getHash().equals(currentBlock.getPreviousHash())) {
 				System.out.println("Previous Hashes not equal");
 				return false;
 			}
+
 			//check if hash is solved
-			if(!currentBlock.hash.substring( 0, difficulty).equals(hashTarget)) {
+			if (!currentBlock.getHash().substring( 0, difficulty).equals(hashTarget)) {
 				System.out.println("This block hasn't been mined");
 				return false;
 			}
-
 		}
 		return true;
 	}
@@ -59,4 +60,5 @@ public static void addBlock(Block newBlock) {
 		newBlock.mineBlock(difficulty);
 		blockchain.add(newBlock);
 	}
+
 }

src/noobchain/StringUtil.java

@@ -13,11 +13,13 @@ public static String applySha256(String input){
 
 			//Applies sha256 to our input, 
 			byte[] hash = digest.digest(input.getBytes("UTF-8"));
-
-			StringBuffer hexString = new StringBuffer(); // This will contain hash as hexidecimal
-			for (int i = 0; i < hash.length; i++) {
-				String hex = Integer.toHexString(0xff & hash[i]);
-				if(hex.length() == 1) hexString.append('0');
+
+			// This will contain hash as hexidecimal
+			StringBuilder hexString = new StringBuilder();
+
+			for (byte aHash : hash) {
+				String hex = Integer.toHexString(0xff & aHash);
+				if (hex.length() == 1) hexString.append('0');
 				hexString.append(hex);
 			}
 			return hexString.toString();
@@ -37,5 +39,4 @@ public static String getDificultyString(int difficulty) {
 		return new String(new char[difficulty]).replace('\0', '0');
 	}
 
-
 }