Programming Assignment - Scrooge Coin

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This is the worst task I have ever done.

TxHandler.java cannot be built and run, everything is a guess. Because I am unfamiliar with JAVA, I encountered millions of syntax errors after submitting.

I have to:

  • Manually import packages
  • Add “;” after each line
  • Add “()” after “if”
  • Declare variable types

This is why I hate JAVA 😡😡😡

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import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

public class TxHandler {

    private UTXOPool utxoPool;
    /**
     * Creates a public ledger whose current UTXOPool (collection of unspent transaction outputs) is
     * {@code utxoPool}. This should make a copy of utxoPool by using the UTXOPool(UTXOPool uPool)
     * constructor.
     */
    public TxHandler(UTXOPool utxoPool) {
        this.utxoPool = new UTXOPool(utxoPool);
    }

    /**
     * @return true if:
     * (1) all outputs claimed by {@code tx} are in the current UTXO pool,
     * (2) the signatures on each input of {@code tx} are valid,
     * (3) no UTXO is claimed multiple times by {@code tx},
     * (4) all of {@code tx}s output values are non-negative, and
     * (5) the sum of {@code tx}s input values is greater than or equal to the sum of its output
     *     values; and false otherwise.
     */
    public boolean isValidTx(Transaction tx) {
        UTXOPool utxoSet = new UTXOPool();
        double pSum = 0;
        double sum = 0;

        for (int i = 0; i < tx.numInputs(); i++) {
            Transaction.Input in = tx.getInput(i);
            UTXO u = new UTXO(in.prevTxHash, in.outputIndex);
            Transaction.Output out = utxoPool.getTxOutput(u);

            if ((!utxoPool.contains(u)) || (!Crypto.verifySignature(out.address, tx.getRawDataToSign(i), in.signature)) || (utxoSet.contains(u))) {
                return false;
            }

            utxoSet.addUTXO(u, out);
            pSum += out.value;
        }

        for (Transaction.Output out : tx.getOutputs()) {
            if (out.value < 0) {
                return false;
            }
            sum += out.value;
        }

        if (pSum < sum) {
            return false;
        }

        return true;
    }

    /**
     * Handles each epoch by receiving an unordered array of proposed transactions, checking each
     * transaction for correctness, returning a mutually valid array of accepted transactions, and
     * updating the current UTXO pool as appropriate.
     */
    public Transaction[] handleTxs(Transaction[] possibleTxs) {
        Set<Transaction> vTxs = new HashSet<>();

        for (Transaction tx : possibleTxs) {
            if (isValidTx(tx)) {
                vTxs.add(tx);

                for (Transaction.Input in : tx.getInputs()) {
                    UTXO u = new UTXO(in.prevTxHash, in.outputIndex);
                    utxoPool.removeUTXO(u);
                }

                for (int i = 0; i < tx.numOutputs(); i++) {
                    Transaction.Output out = tx.getOutput(i);
                    UTXO u = new UTXO(tx.getHash(), i);
                    utxoPool.addUTXO(u, out);
                }
            }
        }

        Transaction[] vTxArr = new Transaction[vTxs.size()];
        return vTxs.toArray(vTxArr);
    }

}

Translated by gpt-3.5-turbo