JAVA While循环在Condition中不识别String.eqauls()

ccrfmcuu 于 4个月前发布在 Java

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好的，我会的我试图让程序识别字母“E”以退出while循环。打印我的结束语句，然后程序就完成了！结束！就是这样！为了测试这一点，我只是试图在提示符要求我输入一个字母时立即退出，但无论它是否识别该字母或任何字母，我都会将其切换到（不是D或W），我已经尝试过

toUpperCase（），在输入后和使用nextLine（）方法时都是如此
while（！DepORWith.equals（“E”）||！DepORWith.equals（“e”））
while（！DepORWith.equals（“E”）&&！DepORWith.equals（“e”））
不断地调换案子
尝试将其全部更改为char类型（大错误）
把一个字母作为一个位置保持器，然后它就会改变
将.equalsIgnoreCase（）与其他“解决方案”一起使用
使用.isEmpty（）

我试过很多次，我不记得了。有些“解决方案”最终会永远循环问题，不管我输入什么。我按E，得到我自己的错误，再按E，它会循环我的错误。上帝，我需要帮助。
我只需要按E，打印not循环语句，然后它退出程序。我把整个代码下来进行全面分析，请。我不先进的Java这是一个介绍Java类，我真的只知道基础知识

import java.util.Scanner ;
import java.io.* ;

public class IOExam {

    public static void main(String[] args) throws IOException
   {
       double Deposit = 0;
       boolean DepStop = false;
       int DEPTransactionNUM = 0;
       double DepTotal = 0; 

       double Withdrawal = 0;
       boolean WithStop = false;
       int WITHTransactionNUM = 0;
       double WithTotal = 0;     

       Scanner keyboard = new Scanner(System.in);

       //Ask For choice 
       String DepORWith = "" ; 

       while (!DepORWith.equals("E"))
       {

           System.out.print("Deposit or Withdrawal D/W ? (Press E to Exit):") ;
           DepORWith = keyboard.nextLine() ;  

           if (DepORWith.equalsIgnoreCase("D"))
            {
                // Create Document First 
           PrintWriter DepositTXT = new PrintWriter ("Deposit.txt");
           DepositTXT.println("Transaction Number \t Amount");
           DepositTXT.println("--------------------------------------");

               //Input Deposit 
               while (DepStop == false)
               {
                   DEPTransactionNUM += 1;

                   System.out.print("Input amount for deposits:") ;
                   Deposit = keyboard.nextDouble() ; 
                   keyboard.nextLine() ; 
                   if (Deposit < 0)
                   {
                       System.out.print("---ERRROR ---\nInput NON NEGATIVE amount for deposits:") ;
                       Deposit = keyboard.nextDouble() ;
                       keyboard.nextLine() ; 

                   }

                   DepTotal = DepTotal + Deposit;

                   DepositTXT.printf("\n\t%d \t\t\t $%,.2f", DEPTransactionNUM, Deposit);

                   String Confirmation ;

                   System.out.print("Would you Like to deposit again? Y/N: ");
                   Confirmation = keyboard.nextLine() ;

                   if (Confirmation.equalsIgnoreCase("y"))
                   {
                       DepStop = false;
                   }
                   else if (Confirmation.equalsIgnoreCase("n"))
                   {
                       DepStop = true; 
                   }
                   else 
                   {
                       System.out.println("---ERRROR ---\nINPUT Y OR N\nWould you Like to deposit again? Y/N") ;
                       Confirmation = keyboard.nextLine() ;
                   }

               }
               DepositTXT.println("\n--------------------------------------");
               DepositTXT.printf("\nTotal \t\t\t $%,.2f", DepTotal);


               DepositTXT.close();
           }

           else if (DepORWith.equalsIgnoreCase("W"))
           {


              // Create Document First 
               PrintWriter WithdrawalTXT = new PrintWriter ("Withdrawal.txt");
               WithdrawalTXT.println("Transaction Number \t Amount");
               WithdrawalTXT.println("--------------------------------------");

               //Input Withdrawals 
               while (WithStop == false)
               {
                   WITHTransactionNUM += 1;

                   System.out.print("Input amount for withdrawal:") ;
                   Withdrawal = keyboard.nextDouble() ; 
                   keyboard.nextLine() ; 
                   if (Withdrawal < 0)
                   {
                       System.out.print("---ERRROR ---\nInput NON NEGATIVE amount for withdrawal:") ;
                       Withdrawal = keyboard.nextDouble() ;
                       keyboard.nextLine() ; 

                   }

                   WithTotal = WithTotal + Withdrawal;

                   WithdrawalTXT.printf("\n\t%d \t\t\t $%,.2f", WITHTransactionNUM, Withdrawal);

                   String Confirmation ;

                   System.out.print("Would you Like to withdrawal again? Y/N: ");
                   Confirmation = keyboard.nextLine() ;

                   if (Confirmation.equalsIgnoreCase("y"))
                   {
                       WithStop = false;
                   }
                   else if (Confirmation.equalsIgnoreCase("n"))
                   {
                       WithStop = true;
                       System.out.print("Deposit or Withdrawal D/W ? (Press E to Exit):") ;
                       DepORWith = keyboard.nextLine() ; 
                   }
                   else 
                   {
                       System.out.println("---ERRROR ---\nINPUT Y OR N\nWould you Like to withdrawal again? Y/N: ") ;
                       Confirmation = keyboard.nextLine() ;
                   }

               }
               WithdrawalTXT.println("\n--------------------------------------");
               WithdrawalTXT.printf("\nTotal \t\t\t $%,.2f", DepTotal);


               WithdrawalTXT.close();

           }

           else 
           {
               System.out.print("---ERRROR ---\nINPUT D OR W OR E \n") ;
               System.out.print("Deposit or Withdrawal D/W ?:") ;
               DepORWith = keyboard.nextLine() ; 
           }
       }
       System.out.printf("Deposit Total: %,.2d \nWithdrawal Total: %,.2d",DepTotal, WithTotal) ;
       System.out.print("\n----------------------------------") ;
       System.out.print("\nThank you for Using Old National") ;
       System.out.print("\n----------------------------------") ;

   }

}

字符串

Java

来源：https://stackoverflow.com/questions/61032098/java-while-loop-not-recignizing-string-eqauls-in-condition

2条答案

按热度按时间

k4ymrczo1#

1.当输入不是E或e时，执行所需的处理
1.最好使用do...while，以避免使用DepORWith = keyboard.nextLine();两次。
按以下步骤操作：

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class Program {

    public static void main(String[] args) throws IOException {
        double Deposit = 0;
        boolean DepStop = false;
        int DEPTransactionNUM = 0;
        double DepTotal = 0;

        double Withdrawal = 0;
        boolean WithStop = false;
        int WITHTransactionNUM = 0;
        double WithTotal = 0;

        Scanner keyboard = new Scanner(System.in);

        // Ask For choice
        String DepORWith = "";
        do {
            System.out.print("Deposit or Withdrawal D/W ? (Press E to Exit):");
            DepORWith = keyboard.nextLine();
            if (!(DepORWith.equalsIgnoreCase("D") || DepORWith.equalsIgnoreCase("W"))) {
                if (!DepORWith.equalsIgnoreCase("E")) {
                    System.out.println("This is not a valid input");
                } else {
                    System.out.println("Goodbye!");
                }
            } else if (!DepORWith.equalsIgnoreCase("E")) {
                if (DepORWith.equalsIgnoreCase("D")) {
                    // Create Document First
                    PrintWriter DepositTXT = new PrintWriter("Deposit.txt");
                    DepositTXT.println("Transaction Number \t Amount");
                    DepositTXT.println("--------------------------------------");

                    // Input Deposit
                    while (DepStop == false) {
                        DEPTransactionNUM += 1;

                        System.out.print("Input amount for deposits:");
                        Deposit = keyboard.nextDouble();
                        keyboard.nextLine();
                        if (Deposit < 0) {
                            System.out.print("---ERRROR ---\nInput NON NEGATIVE amount for deposits:");
                            Deposit = keyboard.nextDouble();
                            keyboard.nextLine();

                        }

                        DepTotal = DepTotal + Deposit;

                        DepositTXT.printf("\n\t%d \t\t\t $%,.2f", DEPTransactionNUM, Deposit);

                        String Confirmation;

                        System.out.print("Would you Like to deposit again? Y/N: ");
                        Confirmation = keyboard.nextLine();

                        if (Confirmation.equalsIgnoreCase("y")) {
                            DepStop = false;
                        } else if (Confirmation.equalsIgnoreCase("n")) {
                            DepStop = true;
                        } else {
                            System.out.println("---ERRROR ---\nINPUT Y OR N\nWould you Like to deposit again? Y/N");
                            Confirmation = keyboard.nextLine();
                        }

                    }
                    DepositTXT.println("\n--------------------------------------");
                    DepositTXT.printf("\nTotal \t\t\t $%,.2f", DepTotal);

                    DepositTXT.close();
                } else if (DepORWith.equalsIgnoreCase("W")) {

                    // Create Document First
                    PrintWriter WithdrawalTXT = new PrintWriter("Withdrawal.txt");
                    WithdrawalTXT.println("Transaction Number \t Amount");
                    WithdrawalTXT.println("--------------------------------------");

                    // Input Withdrawals
                    while (WithStop == false) {
                        WITHTransactionNUM += 1;

                        System.out.print("Input amount for withdrawal:");
                        Withdrawal = keyboard.nextDouble();
                        keyboard.nextLine();
                        if (Withdrawal < 0) {
                            System.out.print("---ERRROR ---\nInput NON NEGATIVE amount for withdrawal:");
                            Withdrawal = keyboard.nextDouble();
                            keyboard.nextLine();

                        }

                        WithTotal = WithTotal + Withdrawal;

                        WithdrawalTXT.printf("\n\t%d \t\t\t $%,.2f", WITHTransactionNUM, Withdrawal);

                        String Confirmation;

                        System.out.print("Would you Like to withdrawal again? Y/N: ");
                        Confirmation = keyboard.nextLine();

                        if (Confirmation.equalsIgnoreCase("y")) {
                            WithStop = false;
                        } else if (Confirmation.equalsIgnoreCase("n")) {
                            WithStop = true;
                            System.out.print("Deposit or Withdrawal D/W ? (Press E to Exit):");
                            DepORWith = keyboard.nextLine();
                        } else {
                            System.out
                                    .println("---ERRROR ---\nINPUT Y OR N\nWould you Like to withdrawal again? Y/N: ");
                            Confirmation = keyboard.nextLine();
                        }

                    }
                    WithdrawalTXT.println("\n--------------------------------------");
                    WithdrawalTXT.printf("\nTotal \t\t\t $%,.2f", DepTotal);

                    WithdrawalTXT.close();

                }
                System.out.printf("Deposit Total: %,.2d \nWithdrawal Total: %,.2d", DepTotal, WithTotal);
                System.out.print("\n----------------------------------");
                System.out.print("\nThank you for Using Old National");
                System.out.print("\n----------------------------------");
            } else {
                System.out.println("Goodbye!");
            }
        } while (!DepORWith.equalsIgnoreCase("E"));
    }
}

字符串

运行示例：

Deposit or Withdrawal D/W ? (Press E to Exit):e
Goodbye!

型

另一个样本运行：

Deposit or Withdrawal D/W ? (Press E to Exit):x
This is not a valid input
Deposit or Withdrawal D/W ? (Press E to Exit):e
Goodbye!

型

另一个样本运行：

Deposit or Withdrawal D/W ? (Press E to Exit):d
Input amount for deposits:

型

另一个样本运行：

Deposit or Withdrawal D/W ? (Press E to Exit):x
This is not a valid input
Deposit or Withdrawal D/W ? (Press E to Exit):d
Input amount for deposits:

型
另外，将代码中的变量名更改为Java naming conventions，例如double Deposit应该是double deposit。

赞(0）回复(0）举报 4个月前

mcdcgff02#

!DepORWith.equals("E") || !DepORWith.equals("e")将始终返回true。如果DepORWith是"E"，则不是e，反之亦然。逻辑上，您需要一个`&&条件：

while (!DepORWith.equals("E") && !DepORWith.equals("e")) {

字符串
虽然在这种情况下，你可以清理一下代码，使用equalsIgnoreCase：

while (!DepORWith.equalsIgnoreCase("E")) {

型

赞(0）回复(0）举报 4个月前

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JAVA While循环在Condition中不识别String.eqauls()

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