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Author: prashant152005

Block chain using Java/Block.java

@@ -0,0 +1,39 @@
+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;
+}
+
+public void mineBlock(int difficulty) {
+String target = new String(new char[difficulty]).replace('\0', '0'); //Create a string with difficulty * "0" 
+while(!hash.substring( 0, difficulty).equals(target)) {
+nonce ++;
+hash = calculateHash();
+}
+System.out.println("Block Mined!!! : " + hash);
+}
+}

Block chain using Java/StringUtil.java

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+import java.security.MessageDigest;
+
+public class StringUtil {
+//Applies Sha256 to a string and returns the result. 
+public static String applySha256(String input){
+try {
+MessageDigest digest = MessageDigest.getInstance("SHA-256"); 
+//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');
+hexString.append(hex);
+}
+return hexString.toString();
+}
+catch(Exception e) {
+throw new RuntimeException(e);
+}
+}
+}