Bank with Exceptions

Lab Java Advanced 30 points

Commands: open NAME, deposit NAME AMT, withdraw NAME AMT, transfer FROM TO AMT, balance NAME. Use a custom BankException for unknown accounts, duplicates, non-positive amounts and insufficient funds, printing error: MESSAGE.

Input

n, then n commands.

Output

Balances and errors.

Example

Input

10
open ann
open bob
deposit ann 100
transfer ann bob 30
withdraw bob 50
balance ann
balance bob
open ann
deposit cy 5
deposit ann -1

Output

error: insufficient funds in bob
ann: 70
bob: 30
error: ann already exists
error: no account cy
error: amount must be positive

Sample input available Sample output available

Editor

Java

Hints

Read all arguments of a command before anything can throw, so input stays in step.

transfer checks the target first, then reuses withdraw and deposit.

Solution explanation

Every rule violation is a BankException, caught in exactly one place in the command loop.

Show solution

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

class BankException extends Exception {
    BankException(String message) {
        super(message);
    }
}

class Bank {
    private final Map<String, Long> accounts = new HashMap<>();

    void open(String name) throws BankException {
        if (accounts.containsKey(name)) throw new BankException(name + " already exists");
        accounts.put(name, 0L);
    }

    long balance(String name) throws BankException {
        Long b = accounts.get(name);
        if (b == null) throw new BankException("no account " + name);
        return b;
    }

    void deposit(String name, long amount) throws BankException {
        if (amount <= 0) throw new BankException("amount must be positive");
        accounts.put(name, balance(name) + amount);
    }

    void withdraw(String name, long amount) throws BankException {
        if (amount <= 0) throw new BankException("amount must be positive");
        long b = balance(name);
        if (amount > b) throw new BankException("insufficient funds in " + name);
        accounts.put(name, b - amount);
    }

    void transfer(String from, String to, long amount) throws BankException {
        balance(to);
        withdraw(from, amount);
        deposit(to, amount);
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Bank bank = new Bank();
        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            String cmd = sc.next();
            try {
                switch (cmd) {
                    case "open": bank.open(sc.next()); break;
                    case "deposit": bank.deposit(sc.next(), sc.nextLong()); break;
                    case "withdraw": bank.withdraw(sc.next(), sc.nextLong()); break;
                    case "transfer": bank.transfer(sc.next(), sc.next(), sc.nextLong()); break;
                    default:
                        String name = sc.next();
                        System.out.println(name + ": " + bank.balance(name));
                }
            } catch (BankException e) {
                System.out.println("error: " + e.getMessage());
            }
        }
    }
}

Output

Answer