Adding source code for the article tracked under BAEL-3232. (#7657)

java-blockchain/src/main/java/com/baeldung/blockchain/Block.java

@@ -0,0 +1,65 @@
+package com.baeldung.blockchain;
+
+import java.io.UnsupportedEncodingException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Date;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class Block {
+
+    private static Logger logger = Logger.getLogger(Block.class.getName());
+
+    private String hash;
+    private String previousHash;
+    private String data;
+    private long timeStamp;
+    private int nonce;
+
+    public Block(String data, String previousHash) {
+        this.data = data;
+        this.previousHash = previousHash;
+        this.timeStamp = new Date().getTime();
+        this.hash = calculateBlockHash();
+    }
+
+    public String mineBlock(int prefix) {
+        String prefixString = new String(new char[prefix]).replace('\0', '0');
+        while (!hash.substring(0, prefix)
+            .equals(prefixString)) {
+            nonce++;
+            hash = calculateBlockHash();
+        }
+        return hash;
+    }
+
+    public String calculateBlockHash() {
+        String dataToHash = previousHash + Long.toString(timeStamp) + Integer.toString(nonce) + data;
+        MessageDigest digest = null;
+        byte[] bytes = null;
+        try {
+            digest = MessageDigest.getInstance("SHA-256");
+            bytes = digest.digest(dataToHash.getBytes("UTF-8"));
+        } catch (NoSuchAlgorithmException | UnsupportedEncodingException ex) {
+            logger.log(Level.SEVERE, ex.getMessage());
+        }
+        StringBuffer buffer = new StringBuffer();
+        for (byte b : bytes) {
+            buffer.append(String.format("%02x", b));
+        }
+        return buffer.toString();
+    }
+
+    public String getHash() {
+        return this.hash;
+    }
+
+    public String getPreviousHash() {
+        return this.previousHash;
+    }
+
+    public void setData(String data) {
+        this.data = data;
+    }
+}