Hi All, so we are back again on track with the third part of Blockchain. So far so good, we discussed about the mining of Blockchain. Enough of theory in first 2 parts. Let’s understand the concepts and basic building blocks using Java. Here we will represent the same concepts of blockchain by different classes (Block [which consists of index, timestamp, previous block’s hash, data of the block], Blockchain [chain or list of blocks] and a demo class to test the same).
Let’s understand the concepts using a small java program.
Before going through the details of coding, let me first tell you what this code is not:
This is not a Blockchain or a network or a distributed ledger.
A basic block of a distributed ledger is represented via a class as below:
package com.example.blockchain;
import java.nio.charset.StandardCharsets;
import java.util.Date;
import com.google.common.hash.Hashing;
/*
* Index
* Time Stamp
* Previous Hash
* Hash
* Data
*/
public class Block {
private int index;
private Date timeStamp;
private String previousHash;
private String hash;
private String data;
// constructor for blockchain values insertion
public Block(Date timeStamp, String previousHash, String data) {
index = 0;
this.timeStamp = timeStamp;
this.previousHash = previousHash;
this.data = data;
this.hash = calculateBlockHash();
}
public String calculateBlockHash() {
String sha256Hash = Hashing.sha256().hashString(data, StandardCharsets.UTF_8).toString();
sha256Hash += timeStamp.toString();
return sha256Hash;
}
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
public Date getTimeStamp() {
return timeStamp;
}
public void setTimeStamp(Date timeStamp) {
this.timeStamp = timeStamp;
}
public String getPreviousHash() {
return previousHash;
}
public void setPreviousHash(String previousHash) {
this.previousHash = previousHash;
}
public String getHash() {
return hash;
}
public void setHash(String hash) {
this.hash = hash;
}
public String getData() {
return data;
}
public void setData(String data) {
this.data = data;
}
}
Using an ArrayList lets create a class which will create a list of blocks, initialize the blocks and add genesis and further blocks:
package com.example.blockchain;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
publicclass BlockChain {
private List<Block> blockChain;
public BlockChain() {
initializeChain();
addGenesisBlock();
}
privatevoid addGenesisBlock() {
blockChain.add(createGenesisBlock());
}
private Block createGenesisBlock() {
returnnew Block(new Date(), null, “{}”);
}
privatevoid initializeChain() {
blockChain = new ArrayList<Block>();
}
public List<Block> getBlockChain() {
return blockChain;
}
publicvoid addBlock(Block block) {
Block latestBlock = getLatestBlock();
block.setIndex(latestBlock.getIndex() + 1);
block.setPreviousHash(latestBlock.getHash());
block.setHash(block.calculateBlockHash());
blockChain.add(block);
}
public Block getLatestBlock() {
return blockChain.get(blockChain.size() – 1);
}
publicvoid setBlockChain(List<Block> blockChain) {
this.blockChain = blockChain;
}
publicvoid blockDisplay() {
for (int i = 0; i < blockChain.size(); i++) {
Block currentBlock = blockChain.get(i);
// Block previousBlock = blockChain.get(i-1);
System.out.println(“Block Values are::::” + “index: ” + currentBlock.getIndex() + “, timeStamp: ”
+ currentBlock.getTimeStamp() + “, previous Hash: ” + currentBlock.getPreviousHash() + “, Hash: ”
+ currentBlock.getHash() + “, data: ” + currentBlock.getData());
}
}
}
Test the class using a demo class with main method:
package com.example.blockchain;
import java.util.Date;
publicclass BlockChainDemoMain {
publicstaticvoid main(String[] args) {
BlockChain bitCoin = new BlockChain();
bitCoin.addBlock(new Block(new Date(), null, “{sender:Deb,receiver:Ari,amount:1500}”));
bitCoin.addBlock(new Block(new Date(), null, “{sender:Ari,receiver:Joy,amount:100}”));
bitCoin.addBlock(new Block(new Date(), null, “{sender:Joy,receiver:Deb,amount:2500}”));
bitCoin.blockDisplay();
}
}
The program uses internal JVM memory so the blockchain lasts till the program is run.
If the same program is run in different nodes of a system which interact through a peer to peer network and which follows other properties of a blockchain network, then the same can be implemented easily as a blockchain.
To be contd..
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