如果我想在用户输入 'n/N' 后终止代码，我应该如何在此代码中编写 'else' 语句？

Question

I am trying to perform arithmetic operations by taking numbers as user input,I want to run the code continuously till user says no. How should I write 'else' statement in this code if I want to terminate the code after user gives input as 'n/N'?


    import java.util.*;
    
    class FirstExample{
        static void arithmetic(){
            Scanner sc = new Scanner(System.in);
            
            while(true){
            System.out.println("\nDo u want to perform the arithmetic operations? (Y/N): ");
            String input = sc.nextLine();
            
            if(input=="y"||input=="Y")
            sc.nextLine();
            System.out.println("Enter first number: ");
            double first = sc.nextDouble();
            System.out.println("Enter second number: ");
            double second = sc.nextDouble();
            System.out.println("Addition of the two number is: "+(first+second));
            System.out.println("Subtraction of the two number is: "+(first-second));
            System.out.println("Multiplication of the two number is: "+(first*second));
            System.out.println("Division of the two number is: "+(first/second));
            sc.nextLine();
            
            }
        }       
        public static void main(String[]args){
            
            FirstExample.arithmetic();  
        }
    }
    ```
    
           //else{
          //    System.exit(0);
          //     }
         //tried adding this block of code but it gets terminated even after giving 'y/Y'

Answer 1

即使您输入 Y 它也会退出的原因是比较 Strings 和 == 将不起作用，因为它比较的是对字符串的引用，而不是字符串中的字符。相反，使用 .equals 方法：

if(input.equals("y") || input.equals("Y"))

Answer 2

一个可能的解决方案是引入一个布尔标志。因此，与其使用 while (true)，还可以将其重构为：

class FirstExample {
    static void arithmetic() {
        Scanner sc = new Scanner(System.in);
     
        boolean shouldStop = false;
            
        while(!shouldStop){
            System.out.println("\nDo u want to perform the arithmetic operations? (Y/N): ");
            String input = sc.nextLine();
            
            if ("n".equalsIgnoreCase(input)) {
                shouldStop = true;
            } else if ("y".equalsIgnoreCase(input)) {
                sc.nextLine();
                System.out.println("Enter first number: ");
                double first = sc.nextDouble();
                System.out.println("Enter second number: ");
                double second = sc.nextDouble();
                System.out.println("Addition of the two number is: "+(first+second));
                System.out.println("Subtraction of the two number is: "+(first-second));
                System.out.println("Multiplication of the two number is: "+(first*second));
                System.out.println("Division of the two number is: "+(first/second));
                sc.nextLine();
            }
        }
    }
}

另外，还有两条评论（有些已经指出）：

使用 equals(String) 或 equalsIgnoreCase(String)（不区分大小写）代替 ==。 equalsIgnoreCase 上的示例可以在 here.
您可以在字符串文字而不是变量上调用 equals()（或 equalsIgnoreCase()）；这是为了避免空指针异常。因此，如果 input 是 null，您可以 "n".equalsIgnoreCase(input) 而不是 input.equalsIgnoreCase("n)。你可以阅读更多 on this SO thread

Answer 3

if (!input.equalsIgnoreCase("y")) {
   break;
}

这里有一些东西。

首先，如前所述，使用 .equals() 或 .equalsIgnoreCase() 比较 java.
其次，摆脱 while 循环中断是这里最简单的事情。
第三，不需要 else 语句，因为您只对此时是否需要停止感兴趣 - 否则您可以继续您正在做的事情。

如果我想在用户输入 'n/N' 后终止代码，我应该如何在此代码中编写 'else' 语句？

How should I write 'else' statement in this code if I want to terminate the code after user gives input as 'n/N'?

java

if-statement

java.util.scanner