如何在帐户上存储和修改余额：

Question

我有一小笔存款，取款，查看余额和退出。 一切都运行得很完美，但是我希望平衡能够根据我的方法（撤回，存款等）进行调整。我从joptionpane开始但是遇到了同样的问题并且认为我应该重新开始。 有人指出我正确的方向吗？

主文件：

import java.util.Scanner;

public class Bank1
{
    public static void main(String[] args) 
    {
        HomeBank obj1 = new HomeBank();

        Scanner keyboard = new Scanner(System.in);
        String option;
        char object;

        System.out.println("This is your home banking account" + "\n");

        do 
        {
            System.out.println("What would you like to do today?"+ "\n" +
                    "\nSelect the following: " +
                    "\n'B' To View Balance." +
                    "\n'D' To Deposit" +
                    "\n'W' To Withdrawal" +
                    "\n'E' To Exit");

            System.out.print("Your selection: ");       

            option = keyboard.next().toUpperCase();
            object = option.charAt(0);

            System.out.print("\n");
            System.out.println("you entered: " +object+ "\n");

            if(object =='D')
                obj1.deposit();
            else if(object =='W')
                obj1.withdrawal();
            else if(object =='B')
                obj1.balance();
            else
                System.out.println("**Invalid input**" +
                        "\n Please try again");            
        } while(object !='E');

        System.out.println("The End");    
    }
}

类：

import java.util.InputMismatchException;
import java.util.Scanner;

public class HomeBank 
{
    private double withdrawal, deposit, balance;

    public HomeBank() 
    {
        balance = 100;
        withdrawal = 50;
        deposit = 150;
    }

    public HomeBank(double bal, double with, double de) 
    {
        balance = bal;
        withdrawal = with;
        deposit = de;
    }

    public static void balance() 
    {
        double balance = 250.00d;

        System.out.println("You have $" + balance+"dollars");  
    }

    public static void deposit() 
    {
        Scanner keyboard = new Scanner(System.in);
        double deposit = 0.00d;
        double balance = 250.00d;
        boolean goodput =true;

        do 
        {
            try 
            {
                System.out.print("How much would you like to deposit today? :");
                deposit = keyboard.nextDouble();

                if(deposit > 0.00) 
                {
                    System.out.println("you entered $" +deposit+" dollars");
                    System.out.println("you now have $" + (deposit + balance)+" dollars");
                    goodput = false;
                }
                else
                {
                    System.out.println("\n**Error**\nYou cannot deposit a "
                            + "negative amount\n");
                    System.out.println("Please try again\n");
                    goodput = true;
                }
            }
            catch (InputMismatchException x) 
            {
                System.out.println("I'm sorry but that is an invalid input" +
                        "\nYou will be redirected to the main menu shortly..."+
                        "\n");
                goodput = false;
            }
        } while (goodput == true); 
    }

    public static void withdrawal() 
    {
        Scanner keyboard = new Scanner(System.in);
        double withdrawal = 0.00d;
        double balance = 250.00d;
        boolean goodput = true;

        do 
        {
            try
            {
                System.out.println("How much would you like to withdrawal?");
                withdrawal = keyboard.nextDouble();

                if (withdrawal < 0 || withdrawal > balance) 
                {
                    System.out.println("You have either entered a negative number"
                            + "or trying to withdrawal more than is in your account");
                    System.out.println("You cannot withdrawal more than $"+balance);
                    System.out.println("Please try again");
                    goodput = true;
                }              
                else 
                {
                    System.out.println("You now have $" +(balance-withdrawal)+ "dollars");
                    System.out.println("Thank you for choosing HomeBank\n"
                            + "\nYou will be redirected to the main menu\n");
                    goodput =false;
                }
            }
            catch (InputMismatchException x) 
            {
                System.out.println("I'm sorry but that is an invalid input" +
                        "\nYou will be redirected to the main menu shortly..."+
                        "\n");
                goodput = false;
            }
        } while (goodput == true);    
    }
}

Answer 1

问题是如何更新值。 在您的方法中，您有类似以下内容：

double deposit = 0.00d;
double balance = 250.00d;

在那里，请注意你如何在变量之前放置double关键字。 通过这样做，您告诉Java在本地范围内创建一个名为deposit and balance的新变量。

如果你想修改名为deposit and balance的字段，你肯定必须在它们之前删除double关键字，并且可以选择放置this. 在变量前面。 它看起来像下面这样：

deposit = 0.00d;
balance = 250.00d;

要么

this.deposit = 0.00d;
this.balance = 250.00d;

您将替换所有变量withdraw ， balance和deposit实例，但仅限于声明。

您不需要指定类型的原因是因为您已在字段声明中定义它。 因此，当您再次在方法中定义它时，您要创建一个具有该名称的新变量并在当前范围中键入。

编辑：正如Suyash Limaye所说，你必须从方法中删除static关键字。 使用static关键字可以防止方法访问非静态字段，从而导致冲突。