Throwing own exceptions

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I have this class Account

    import java.io.IllegalArgumentException;

    class Account {
        final int accountNo;
        final Customer owner;
        final double overdraft;

        double balance = 0;

        private Account(int accountNo, Customer owner, double overdraft) {
            this.accountNo = accountNo;
            this.owner = owner;
            this.overdraft = overdraft;
        }

        void print() {
            Out.println("Kontonummer: " + accountNo);
            owner.print();
            Out.format("Kontostand: %.2f%nÜberziehungsrahmen: %.2f%n", balance, overdraft);
        }

        public boolean deposit(double amount) throws IllegalArgumentException {
            if (amount <= 0) {
                throws new IllegalArgumentException("Cannot deposit negative amounts!");
                break;
            } else {
                balance += amount;
                return true;
            }

            public boolean withdraw(double amount) throws OverdraftLimitReachedException {
                if (amount <= 0 || !isCovered(amount)) {
                    throw new OverdraftLimitReachedException("Overdraft limit has been reached", accountNo);
                    break;
                } else {
                    balance -= amount;
                    return true;
                }

                boolean isCovered(double amount) {
                    return amount - overdraft <= balance;
                }

                boolean transfer(Account target, double amount) {
                    boolean success = withdraw(amount);
                    if (!success) return false;

                    target.deposit(amount);
                    return true;
                }
            }
        }
    }

Now I also have this exception that I wrote

    public class NoSuchAccountException extends AccountException {

        public NoSuchAccountException(int accountNo) {
            super(message, accountNo);
        }
    }

Now I need to throw this exception in the class account,when the searched account number does not exist.Now my question is in which method(or function I think that is the same,please correct me if I’m wrong) do I throw this exception.And after what check.How would I check if the account number exist,and if it doesnt I’ll throw this exception. Thank you!

EDIT: The class banking, to complete the program

class Banking {
  static final int CAPACITY = 100;

  final Account[] accounts = new Account[CAPACITY];
  int nOfAccounts = 0;

  int createAccount(String firstName, String lastName, String phone, double overdraft) {
    if (nOfAccounts == CAPACITY) return -1;

    // use nOfAccounts as accountNo and index to array
    Customer owner = new Customer(firstName, lastName, phone);
    Account account = new Account(nOfAccounts, owner, overdraft);
    accounts[nOfAccounts] = account;
    nOfAccounts++;

    return account.accountNo;
  }

  boolean deposit(int accountNo, double amount) {
    if (accountNo < 0 || accountNo >= nOfAccounts) return false;

    Account account = accounts[accountNo];
    return account.deposit(amount);
  }

  boolean withdraw(int accountNo, double amount) {
    if (accountNo < 0 || accountNo >= nOfAccounts) return false;

    Account account = accounts[accountNo];
    return account.withdraw(amount);
  }

  boolean transfer(int fromNo, int toNo, double amount) {
    if (fromNo < 0 || toNo < 0 ||
        fromNo >= nOfAccounts || toNo >= nOfAccounts) return false;

    Account from = accounts[fromNo];
    Account to = accounts[toNo];
    return from.transfer(to, amount);
  }

  double getBalance(int accountNo) {
    if (accountNo < 0 || accountNo >= nOfAccounts) return 0;

    Account account = accounts[accountNo];
    return account.balance;
  }

  double getBalance() {
    double sum = 0;

    for (int i = 0; i < nOfAccounts; i++) {
      sum += accounts[i].balance;
    }
    return sum;
  }

  void print() {
    Out.println("---------- Bankauszug ----------");

    for (int i = 0; i < nOfAccounts; i++) {
      accounts[i].print();
      Out.println("--------------------------------");
    }
    Out.format("Bilanzsumme: %.2f%n", getBalance());
    Out.println("--------------------------------");
  }

  // --------------------- Optionaler Teil ---------------------

  public static void main(String[] args) {
    Banking banking = new Banking();
    char op;

    do {
      printMenu();
      op = readOperation();

      switch (op) {
        case 'a': {
          printTitle("Konto anlegen");
          String firstName = getString("Vorname");
          String lastName = getString("Nachname");
          String phone = getString("Telefonnummer");
          double overdraft = getDouble("Überziehungsrahmen");

          int accountNo = banking.createAccount(
            firstName, lastName, phone, overdraft);
          printMessage("Anlegen von Konto " + accountNo, accountNo != -1);
          break;
        }
        case 'e': {
          printTitle("Einzahlen");
          int accountNo = getInt("Kontonummer");
          double amount = getDouble("Einzahlungsbetrag");

          boolean success = banking.deposit(accountNo, amount);
          printMessage("Einzahlen", success);
          break;
        }
        case 'b': {
          printTitle("Abheben");
          int accountNo = getInt("Kontonummer");
          double amount = getDouble("Abhebungsbetrag");

          boolean success = banking.withdraw(accountNo, amount);
          printMessage("Abheben", success);
          break;
        }
        case 't': {
          printTitle("Überweisen");
          int fromNo = getInt("Von Kontonummer");
          int toNo = getInt("Auf Kontonummer");
          double amount = getDouble("Betrag");

          boolean success = banking.transfer(fromNo, toNo, amount);
          printMessage("Überweisen", success);
          break;
        }
        case 'd':
          banking.print();
          break;
        case 'q':
          Out.println("Beenden");
          break;
        default:
          Out.println("Ungültige Operation");
          break;
      }
    } while(op != 'q');
  }

  static void printMenu() {
    Out.println();
    Out.println("*********** Bankverwaltung ********");
    Out.println("Konto anlegen ................... a");
    Out.println("Einzahlen ....................... e");
    Out.println("Beheben ......................... b");
    Out.println("Überweisen ...................... t");
    Out.println("Übersicht drucken ............... d");
    Out.println("Beenden ......................... q");
    Out.print("Welche Menuoption? [a|e|b|t|d|q]: ");
  }

  static char readOperation() {
    char ch = Character.toLowerCase(In.readChar());
    In.readLine();
    return ch;
  }

  static void printTitle(String text) {
    Out.println("*** " + text + " ***");
  }

  static String getString(String text) {
    Out.print(text + ": ");
    return In.readLine();
  }

  static double getDouble(String text) {
    Out.print(text + ": ");
    return In.readDouble();
  }

  static int getInt(String text) {
    Out.print(text + ": ");
    return In.readInt();
  }

  static void printMessage(String operation, boolean success) {
    String message = success ?
      operation + " erfolgreich durchgeführt" :
      "Ungültige Operation";
    Out.println(message);
  }
}

Answer

Extract the common place for acquiring the account

private Acount getAccount(accountNo) {
  if (accountNo >= accounts.length || accounts[accountNo] == null) {
   throw new NoSuchAccountException();
  }
  return account;
}


  boolean deposit(int accountNo, double amount) {
    Account account = getAccount(accountNo);
    return account.deposit(amount);
  }



Source: stackoverflow