Repository: CryptoKass/NoobChain-Tutorial-Part-1
Branch: master
Commit: 2fb61b75649e
Files: 5
Total size: 5.9 KB

Directory structure:
gitextract_d2jvv62y/

├── LICENSE
├── README.md
└── src/
    └── noobchain/
        ├── Block.java
        ├── NoobChain.java
        └── StringUtil.java

================================================
FILE CONTENTS
================================================

================================================
FILE: LICENSE
================================================
MIT License

Copyright (c) 2017 Kassius 

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


================================================
FILE: README.md
================================================
# NoobChain-Tutorial-Part-1
A Simple Java Blockchain for educational purposes. 

This is for https://medium.com/programmers-blockchain/create-simple-blockchain-java-tutorial-from-scratch-6eeed3cb03fa tutorial.
*If you have any other questions you can message me on the [Blockchain Developers Club](https://discord.gg/ZsyQqyk) discord server.*

# Dependencies: You will need to import GSON:
- gson [gson-2.8.2.jar](http://central.maven.org/maven2/com/google/code/gson/gson/2.8.2/gson-2.8.2.jar)

# Java Version:
- JDK1.8.0_77

contact: kassCrypto@gmail.com


================================================
FILE: src/noobchain/Block.java
================================================
package noobchain;

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);
	}
	
}


================================================
FILE: src/noobchain/NoobChain.java
================================================
package noobchain;
import java.util.ArrayList;
import com.google.gson.GsonBuilder;

public class NoobChain {
	
	public static ArrayList<Block> blockchain = new ArrayList<Block>();
	public static int difficulty = 5;

	public static void main(String[] args) {	
		//add our blocks to the blockchain ArrayList:
		
		System.out.println("Trying to Mine block 1... ");
		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));
		
		System.out.println("Trying to Mine block 3... ");
		addBlock(new Block("Hey im the third block",blockchain.get(blockchain.size()-1).hash));	
		
		System.out.println("\nBlockchain is Valid: " + isChainValid());
		
		String blockchainJson = StringUtil.getJson(blockchain);
		System.out.println("\nThe block chain: ");
		System.out.println(blockchainJson);
	}
	
	public static Boolean isChainValid() {
		Block currentBlock; 
		Block previousBlock;
		String hashTarget = new String(new char[difficulty]).replace('\0', '0');
		
		//loop through blockchain to check hashes:
		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()) ){
				System.out.println("Current Hashes not equal");			
				return false;
			}
			//compare previous hash and registered previous hash
			if(!previousBlock.hash.equals(currentBlock.previousHash) ) {
				System.out.println("Previous Hashes not equal");
				return false;
			}
			//check if hash is solved
			if(!currentBlock.hash.substring( 0, difficulty).equals(hashTarget)) {
				System.out.println("This block hasn't been mined");
				return false;
			}
			
		}
		return true;
	}
	
	public static void addBlock(Block newBlock) {
		newBlock.mineBlock(difficulty);
		blockchain.add(newBlock);
	}
}


================================================
FILE: src/noobchain/StringUtil.java
================================================
package noobchain;
import java.security.MessageDigest;

import com.google.gson.GsonBuilder;

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);
		}
	}
	
	//Short hand helper to turn Object into a json string
	public static String getJson(Object o) {
		return new GsonBuilder().setPrettyPrinting().create().toJson(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');
	}
	
	
}