如何跟踪银行帐户上的余额？

Question

I am going to create a program that keeps track of the balance on a bank account. The program shall use a loop that continues until the user choses to exit by answering no to the question Do you want to continue? .

In the loop the user shall be asked to enter an amount (positive for deposit and negative for withdraw). The amount shall be added/subtracted from an account balance variable. All deposits/withdraws shall be saved as a history so that we can print it later. When the user choses to exit the loop the current account balance together with the account history (from the array/ArrayList) shall be printed.

Now, I want to use an array with ten slots for the history feature.

My question is how can I keep track of the all deposit, withdraw and current account balance (using an array with ten slots for the history feature) so that I can print it out while the user exits the program?

My code:

BankApp class:

package bankapp;

import java.util.Scanner;

public class BankApp {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        askingUser au = new askingUser();

        System.out.println("WELCOME TO OUR BANK!\nYou have 100 SEK by default in your account.");

        while (true) {

            au.userInput();

            System.out.println("Do you want to continue? Answer by Yes or No.");
            String yesOrNo = input.next();

            if (yesOrNo.equalsIgnoreCase("yes")) {

                au.userInput();

            } else if (yesOrNo.equalsIgnoreCase("no")) {
                System.out.println("History: ");

                //print out the transaction history
                System.exit(0);

            } else {

                System.out.println("Invalid character input.");

            }

        }

    }
}

askingUser class:

package bankapp;

import java.util.Scanner;

public class askingUser {

    Scanner input = new Scanner(System.in);
    double initialBal = 100;

    public void userInput() {
        System.out.println("Enter your amount: (+ve for deposit & -ve for withdraw)");
        double inputAmount = input.nextDouble();

        if (inputAmount >= 0) {

            double newPosAm = initialBal + inputAmount;
            System.out.println("Your current balance is: " + newPosAm + " SEK");

        } else {

            double newNegAm = initialBal + inputAmount;
            System.out.println("Your current balace is: " + newNegAm + " SEK");
        }

    }

}

Answer 1

If you use an array, you have to keep track of the number of elements stored inside and resize the array when necessary. The easiest way would be to keep the history as strings in ArrayList . You would add one message to that list per transaction:

ArrayList<String> history = new ArrayList<String>();

void addToHistory(String transaction) {
    history.add(transaction);
}

void printHistory() {
    for(String s : history) {
        System.out.println(s);
    }
}

addToHistory("Withdrawal: 100 SEK" );
addToHistory("Deposit: 200 SEK" );
printHistory();

Answer 2

You need a queue to do that. However, for a simple, fast and primitive implementation you can:

• Define an object called Transaction ( deposit - double, withdraw - double, current account balance - double )
• Add a List of Transaction s into askingUser class as an attribute . I strongly recommend renaming the class name to AskingUser to make it seen as object.
• At each operation add a new Transaction to end of the List you just added.
• At exit, print out the last -say- 10 elements of the List ; you can reach it through askingUser object. You can also define a function in askingUser class to print out the last 10 elements, if you make the function work according to selected number of elements, you can add number of Transaction s to the function's inputs.