调用方法但没有返回 java

Question

在从另一个非常有帮助的成员那里获得一些帮助后，我陷入了另一个困境，

import java.util.Scanner;

public class assn10
{
    public static void main(String[] args)
    {
       Scanner stdIn = new Scanner(System.in); 
       String act = "MUSH";
       double bal = 0.0;
       double inc = 0.0;

       while (act.charAt(0) != 'Q')
       {
           System.out.print((char)27 + "[2J");
           System.out.print("## IT\'S A BANK ##\nD - Deposit\nW - Withdraw\nI - Interest\nB - Balance\nQ - Quit\n\nAction:");
           act = stdIn.next();
           act = act.toUpperCase();
       }

       switch (act.charAt(0))
       {
       case 'D': 
           deposit(stdIn);
           break;
       case 'W': 
           withdraw(stdIn);
           break;
       case 'I':
           interest(stdIn);
           break;
       case 'B':
           balence(stdIn);
           break;
       }
   }   

   public static void deposit(Scanner stdIn) 
   {
       System.out.print((char)27 + "[2J");
       System.out.print("Deposit how much?:"); 
       inc = stdIn.nextDouble();

       while (inc < 0)
       { 
           System.out.print("Deposits must be non-negative. Please try again:");
           inc = stdIn.nextDouble();
       }

       bal += inc;
   }

   public static void withdraw(Scanner stdIn) 
   {
       System.out.print((char)27 + "[2J");
       System.out.print("Withdraw how much?:"); 
       inc = stdIn.nextDouble();

       while (inc < 0)
       {
           System.out.print("Withdrawalas must be non-negative. Please try again:");
           inc = stdIn.nextDouble();
       } 
       while (inc > bal)
       {
           System.out.print("Insufficient funds. Please try a lower amount:");
           inc = stdIn.nextDouble();
       } 

       bal -= inc;
   }

   public static void interest(Scanner stdIn) 
   {
       System.out.print((char)27 + "[2J");
       inc = bal*.04;
       bal += inc;
       System.out.print("Interest accrued: $" + inc + "; press enter key to return to menu."); 
       stdIn.nextLine();
       stdIn.nextLine();
   }

   public static void balence(Scanner stdIn) 
   {    
       System.out.print((char)27 + "[2J");
       System.out.print("Balance = $" + bal + "; press enter key to return to menu."); 
       stdIn.nextLine(); 
       stdIn.nextLine();
   }
}

我在想我需要将一个值返回到主要参数？开关功能的接收会收到什么？

Answer 1

上帝啊，试试这个吧。看到区别了吗？

import java.util.Scanner;

public class assn10
{
    static double bal = 0.0;
    static double inc = 0.0;


    public static void main(String[] args)
    {
       Scanner stdIn = new Scanner(System.in);
       String act = "MUSH";

       while (act.charAt(0) != 'Q')
       {
           System.out.print((char)27 + "[2J");
           System.out.print("## IT\'S A BANK ##\nD - Deposit\nW - Withdraw\nI - Interest\nB - Balance\nQ - Quit\n\nAction:");
           act = stdIn.next();
           act = act.toUpperCase();
           switch (act.charAt(0))
           {
           case 'D':
               deposit(stdIn);
               break;
           case 'W':
               withdraw(stdIn);
               break;
           case 'I':
               interest(stdIn);
               break;
           case 'B':
               balance(stdIn);
               break;
           }
       }
   }

   public static void deposit(Scanner stdIn)
   {
       System.out.print((char)27 + "[2J");
       System.out.print("Deposit how much?:");
       inc = stdIn.nextDouble();

       while (inc < 0)
       {
           System.out.print("Deposits must be non-negative. Please try again:");
           inc = stdIn.nextDouble();
       }

       bal += inc;
   }

   public static void withdraw(Scanner stdIn)
   {
       System.out.print((char)27 + "[2J");
       System.out.print("Withdraw how much?:");
       inc = stdIn.nextDouble();

       while (inc < 0)
       {
           System.out.print("Withdrawalas must be non-negative. Please try again:");
           inc = stdIn.nextDouble();
       }
       while (inc > bal)
       {
           System.out.print("Insufficient funds. Please try a lower amount:");
           inc = stdIn.nextDouble();
       }

       bal -= inc;
   }

   public static void interest(Scanner stdIn)
   {
       System.out.print((char)27 + "[2J");
       inc = bal*.04;
       bal += inc;
       System.out.print("Interest accrued: $" + inc + "; press enter key to return to menu.");
       stdIn.nextLine();
       stdIn.nextLine();
   }

   public static void balance(Scanner stdIn)
   {
       System.out.print((char)27 + "[2J");
       System.out.print("Balance = $" + bal + "; press enter key to return to menu.");
       stdIn.nextLine();
       stdIn.nextLine();
   }
}

Answer 2

为什么你觉得你需要返回一个值？也许每个方法都应该只打印其结果。

Answer 3

这里有几个主要问题。
您需要考虑变量的范围 - 例如 inc 和 bal

该变量是 main() 方法的本地变量，其他方法无法看到（例如 Deposit()）

您可以通过多种方式修复此问题，最简单（也可能是最糟糕）的方法是使该变量成为静态类变量，如下所示：

public class assn10
{
    private static double bal = 0.0;
    private static double inc = 0.0;

    public static void main(String[] args)
    {
       Scanner stdIn = new Scanner(System.in); 
       String act = "MUSH";
//.....

然后类中的每个方法都可以访问单类作用域变量 bal 和 inc。

另外，如果您希望能够在一次运行中执行多个操作（我假设您这样做），那么您的开关可能应该位于 while ( != 'Q' ) 循环内。