java - 银行账户程序问题

Question

对于我的 Java 类，我们需要创建一个银行帐户，该帐户具有取款、存款和显示当前余额的方法。在 Tester 类中，我想让它询问姓名、余额，然后让你选择 1、2 或 3。然后它重复你选择的选项，直到你说键入“n”。问题是运行这段代码会导致它在你存钱后说“你存入了(存入的金额)账户(账户名称)。你的新余额是(这个)。”它说“this”的部分与存入的金额完全相同。换句话说，它不添加它，它只是使新余额与存款相同，而不管之前有多少。有什么帮助吗？谢谢。

import java.io.*;
import java.util.*;
public class BankAccount
{
    public BankAccount(double b, String n)
    {
        double balance = b;
        String name = n;
    }
    public void deposit(double d)
    {
        balance += d;
    }
    public void withdraw(double w)
    {
        balance -= w;
    }
    public String nickname()
    {
        System.out.print("Enter a new name: ");
        Scanner kbIn = new Scanner(System.in);
        String n = kbIn.nextLine();
        return n;
    }
    double balance;
    String name;
}

测试类:

import java.io.*;
import java.util.*;
public class Tester
{
    public static void main(String args[])
    {
        Scanner kbInLine = new Scanner(System.in);
        Scanner kbIn = new Scanner(System.in);

        System.out.print("Enter your name: ");
        String name = kbInLine.nextLine();

        System.out.print("Please enter balance: $");
        double balance = kbIn.nextDouble();

        BankAccount myAccount = new BankAccount(balance, name);
        String proceed = "y";

        while(proceed.equalsIgnoreCase("y"))
        {
            System.out.println("\nPlease pick a number. Would you like to...\n\t 1. Deposit\n\t 2. Withdraw\n\t 3. Print Balance\n");
            int choice = kbIn.nextInt();

            switch(choice)
            {
                case 1:
                    System.out.print("How much would you like to deposit?\n\t$");
                    double deposit = kbIn.nextDouble();
                    myAccount.deposit(deposit);
                    System.out.println("You have deposited $" + deposit + " into the account of " + name + ". The new balance is: " + myAccount.balance);
                    break;
                case 2:
                    System.out.print("How much would you like to withdraw?\n\t$");
                    double withdraw = kbIn.nextDouble();
                    if(myAccount.balance - withdraw > 0)
                    {
                        myAccount.withdraw(withdraw);
                        System.out.println("You have withdrawn $" + withdraw + " from the account of " + name + ". The new balance is: " + myAccount.balance);
                    }
                    else    
                    {
                        System.out.println("Sorry, you have insufficient funds for this operation. Your existing balance is $" + myAccount.balance);
                    }
                    break;
                case 3:
                    System.out.print("The balance in the account of " + name + " is $" + myAccount.balance);
                    break;
            }
            System.out.print("\nWould you like to do another transaction? (Y/N)");
            proceed = kbIn.next();
        }
        System.out.println("\nThank you for banking with us. Have a good day!");
    }
}

真正奇怪的是，我之前做过一个项目(实际上是一个简化版本)，它存入并提取预定的编码金额，然后输出新的银行余额，它做得很好.但是 BankBalance 的代码是相同的。这是这些的代码。
BankAccount 类是:

public class BankAccount
{
    public BankAccount(String nm, double amt) // Constructor
    {
        name = nm;
        balance = amt;
    }
    public void deposit(double d) // Sets up deposit object as balance += d
    {
        balance += d;
    }
    public void withdraw(double w) // Sets up withdraw object as balance -= w
    {
        balance -= w;
    }

    public double balance;
    public String name;
}

Tester 类是:

import java.io.*;
import java.util.*;
public class Tester
{
    public static void main(String args[])
    {
        Scanner kbIn = new Scanner(System.in);
        System.out.print("Enter your name:");
        String name = kbIn.nextLine();

        System.out.print("Enter the balance:");
        double balance = kbIn.nextDouble();

        BankAccount myAccount = new BankAccount(name, balance);
        myAccount.deposit(505.22);
        System.out.println(myAccount.balance);
        myAccount.withdraw(100.00);

        System.out.println("The " + myAccount.name + " account balance is, $" + myAccount.balance);
    }
}

Answer 1

你实际上并没有在这里初始化你的 balance 成员变量:

public BankAccount(double b, String n)
{
    double balance = b;

这将创建一个名为 balance 的新本地 变量，您可以将 b 的值分配给该变量。在此构造函数运行后，成员 变量 balance 将保持为 0(默认值)。