Cleanup code

src/noobchain/Block.java

@@ -3,41 +3,40 @@
 import java.util.Date;
 
 public class Block {
-
-	public String hash;
-	public 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;
-
-	//Block Constructor.  
-	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.
-	}
-
-	//Calculate new hash based on blocks contents
-	public String calculateHash() {
-		String calculatedhash = StringUtil.applySha256( 
-				previousHash +
-				Long.toString(timeStamp) +
-				Integer.toString(nonce) + 
-				data 
-				);
-		return calculatedhash;
-	}
-
-	//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)) {
-			nonce ++;
-			hash = calculateHash();
-		}
-		System.out.println("Block Mined!!! : " + hash);
-	}
-
+
+    public String hash;
+    public String previousHash;
+    private final String data; //our data will be a simple message.
+    private final long timeStamp; //as number of milliseconds since 1/1/1970.
+    private int nonce;
+
+    //Block Constructor.
+    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.
+    }
+
+    //Calculate new hash based on blocks contents
+    public String calculateHash() {
+        return StringUtil.applySha256(
+                previousHash +
+                        timeStamp +
+                        nonce +
+                        data
+        );
+    }
+
+    //Increases nonce value until hash target is reached.
+    public void mineBlock(int difficulty) {
+        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);
+    }
+
 }

src/noobchain/StringUtil.java

@@ -1,4 +1,5 @@
 package noobchain;
+import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 
 import com.google.gson.GsonBuilder;
@@ -12,12 +13,12 @@ public static String applySha256(String input){
 			MessageDigest digest = MessageDigest.getInstance("SHA-256");
 
 			//Applies sha256 to our input, 
-			byte[] hash = digest.digest(input.getBytes("UTF-8"));
+			byte[] hash = digest.digest(input.getBytes(StandardCharsets.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');
+			StringBuilder hexString = new StringBuilder(); // This will contain hash as hexidecimal
+			for (byte b : hash) {
+				String hex = Integer.toHexString(0xff & b);
+				if (hex.length() == 1) hexString.append('0');
 				hexString.append(hex);
 			}
 			return hexString.toString();
@@ -33,8 +34,8 @@ public static String getJson(Object o) {
 	}
 
 	//Returns difficulty string target, to compare to hash. eg difficulty of 5 will return "00000"  
-	public static String getDificultyString(int difficulty) {
-		return new String(new char[difficulty]).replace('\0', '0');
+	public static String getDifficultyString(int difficulty) {
+		return "0".repeat(difficulty);
 	}