Stage #2: A proof of work concept

src/blockchain/Blockchain.java

@@ -0,0 +1,121 @@
+package blockchain;
+import java.io.Serializable;
+import java.security.MessageDigest;
+import java.time.LocalTime;
+import java.util.Scanner;
+
+public class Blockchain implements Serializable {
+
+    private String nonce = "";
+    int starthash = 0;
+    String previoushash = Integer.toString(starthash);
+    String currenthash = "";
+    private int tiktok;
+
+
+    Blockchain() {
+
+
+        int id = 1;
+        int time;
+        Boolean sec;
+        int zeros;
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("Enter how many zeros the hash must starts with: ");
+        zeros = scanner.nextInt();
+
+        for (int i = 0;  i < zeros; i ++){
+            nonce+="0";
+        }
+        System.out.print("Enter how many block will created: ");
+
+        time = scanner.nextInt();
+
+
+
+        for (int i = 0; i < time; i++) {
+            System.out.println("Block:");
+            System.out.println("id: " + id);
+
+            currenthash = proofOfWork(previoushash); 
+            getTimeStamp();
+
+            System.out.println("Hash of the previous block: " + previoushash);
+            System.out.println("Hash of the block: " + currenthash);
+            System.out.println("Block was generating for " + tiktok + " seconds");
+
+            sec = validate(previoushash, currenthash);
+
+            if (sec) {
+                previoushash = currenthash;
+                id++;
+                System.out.println();
+            } else {
+                System.out.println("Hash not valid!!!");
+
+                break;
+            }
+        }
+    }
+
+    private void getTimeStamp() {
+        System.out.println("Timestamp: " + System.currentTimeMillis());
+    }
+
+
+    private String proofOfWork(String block) {
+
+        String nonceKey = nonce;
+        long nonce = 0;
+        boolean nonceFound = false;
+        String nonceHash = "";
+
+
+        LocalTime time_before = LocalTime.now();
+
+        while (!nonceFound) {
+
+            nonceHash = GenerateBlock(block + nonce);
+
+            nonceFound = nonceHash.substring(0, nonceKey.length()).equals(nonceKey);
+            nonce++;
+
+        }
+
+        LocalTime time_after = LocalTime.now();
+        //считаем разницу во времени
+        this.tiktok = (time_after.getMinute()-time_before.getMinute())*60 + (time_after.getSecond()-time_before.getSecond());
+        return nonceHash;
+
+    }
+
+    private Boolean validate(String previousblock, String currentblock) {
+        String check = proofOfWork(previousblock);
+        if(check.equals(currentblock)){
+            return true;
+        }else {
+            return false;
+        }
+    }
+
+    private String GenerateBlock(String currentid) {
+        try {
+            MessageDigest digest = MessageDigest.getInstance("SHA-256");
+            /* Applies sha256 to our input */
+            byte[] hash = digest.digest(currentid.getBytes("UTF-8"));
+            StringBuilder hexString = new StringBuilder();
+            for (byte elem: hash) {
+                String hex = Integer.toHexString(0xff & elem);
+                if(hex.length() == 1) hexString.append('0');
+                hexString.append(hex);
+            }
+            return hexString.toString();
+        }
+        catch(Exception e) {
+            throw new RuntimeException(e);
+        }
+
+    }
+
+}

src/blockchain/Main.java

@@ -1,7 +1,30 @@
 package blockchain;
 
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+
 public class Main {
+
     public static void main(String[] args) {
-        System.out.print("Hello world!");
+        new Blockchain();
+        FileOutputStream fos = null;
+        ObjectOutputStream oos = null;
+        try {
+            fos = new FileOutputStream("temp.out");
+            oos = new ObjectOutputStream(fos);
+        } catch (IOException e) {
+            System.out.println("Exit");
+        }
+        Blockchain b = new Blockchain();
+
+        try {
+            oos.writeObject(b);
+            oos.flush();
+            oos.close();
+        } catch (IOException e) {
+            System.out.println("Smth wrong");
+        }
+
+    }
     }
-}