Main.java

public static void main(String[] args) { 
  try { 
    var blockChain = new BlockChain(); 
    
    Block block1 = new Block("Hello"); 
    Block block2 = new Block("World"); 
    Block block3 = new Block("Whatever"); 
    
    blockChain.addBlock(block1); 
    blockChain.addBlock(block2); 
    blockChain.addBlock(block3); 
    
    for (Block block: blockChain.chain) { 
      System.out.println(block); 
    } 
    
    System.out.println("Is valid chain : " + blockChain.isValid()); 
    
    // modify second block's data.. 
    blockChain.chain.get(1).transactionData = "World1"; 
    System.out.println("Is valid chain : " + blockChain.isValid()); // will be false 
  } 
  catch(Exception e) { 
    System.err.println(e); 
  }
}