從掃描儀讀取字符

Question

對不起Noob問題。這是我第一天嘗試Java編程。我需要幫助檢索用戶想要使用整數的操作符的用戶輸入。

import java.util.Scanner; 

public class calculator { 

    public static void main (String args[]) { 

     Scanner number = new Scanner(System.in); 
     double num1,num2,answer; 
     char operator; 

     System.out.println("Enter first number: "); 
     num1 = number.nextDouble(); 

     operator = number.nextChar(); /* the "nextChar" is not correct */ 

     System.out.println("Enter second number: "); 
     num2 = number.nextDouble(); 

     if (operator = '+'){ 
      answer = num1 + num2; /* If statements do not work like this */ 
     }        /* I would use "else if", unsure if it allows */ 
     if (operator = '-'){ 
      answer = num1 - num2; 
     } 
     if (operator = '*'){ 
      answer = num1 - num2; 
     } 
     if (operator = '/'){ 
       answer = num1/num2; 
     } 

     System.out.println(num1 + num2 + operator + answer); 

    } 
} 

編輯後的版本：

import java.util.Scanner; 

public class calculator{ 

    public static void main (String args[]) { 

     Scanner userInput = new Scanner(System.in); 

     String operator; 
     double num1,num2,answer = 0; 



     System.out.println("Enter first number: "); 
     num1 = userInput.nextDouble(); 

     System.out.println("Enter operator: "); 
     operator = userInput.next(); 


     System.out.println("Enter second number: "); 
     num2 = userInput.nextDouble(); 

     if (operator.equals ("+")){ 
      answer = num1 + num2; 
     } 
     else if (operator.equals ("-")){ 
      answer = num1 - num2; 
     } 
     else if (operator.equals ("*")){ 
      answer = num1 * num2; 
     } 
     else if (operator.equals ("/")){ 
       answer = num1/num2; 
     } 

     System.out.println("First number:" + num1); 
     System.out.println("Operator:" + operator); 
     System.out.println("Second number:" + num2); 

     System.out.println("Answer: " + answer); 
    } 
} 

第一個數字：10.0

運營商：*

第二個數字：3.14

答：31.400000000000002

非常感謝！幫了很多！

Answer 1

好的。這工作，並可以幫助你在你的道路上的java

public class Tester4 { 

    public static void main(String args[]) { 

     Scanner input = new Scanner(System.in); 
     double num1, num2, answer = 0; 
     String operator; 

     System.out.println("Enter first number: "); 
     num1 = input.nextDouble(); 

     System.out.println("Enter operator: "); 
     operator = input.next(); 

     System.out.println("Enter second number: "); 
     num2 = input.nextDouble(); 

     if(operator.equals("+")) { 
      answer = num1 + num2; 
     } else if(operator.equals("-")) { 
      answer = num1 - num2; 
     } else if(operator.equals("*")) { 
      answer = num1 - num2; 
     } else if(operator.equals("/")) { 
      answer = num1/num2; 
     } 

     System.out.println("First number:" + num1); 
     System.out.println("Operator:" + operator); 
     System.out.println("Second number:" + num2); 

     System.out.println("Answer: " + answer); 
    } 

} 

Answer 2

在比較中使用==，而不是=（表示分配）。

Answer 3

您需要使用

if (operator == '+') 

通知 '雙等於'。

Answer 4

正如其他已經指出的那樣，使用==運算符來檢查相等性。 =運算符將分配值。

爲了讀取Scanner中的單個字符，請查看以下問題：Scanner method to get a char。在那裏，您會發現使用Scanner.findInLine()方法的建議，該方法接收正則表達式作爲參數。提供.通配符作爲模式，你將能夠得到一個字符串和下一個字符，並使用charAt(0)就可以得到它作爲char。

Scanner sc = new Scanner("abc"); 
char ch = sc.findInLine(".").charAt(0); 
System.out.println(ch); // prints "a" 

當然，你也可以只使用Scanner.next()獲得下一個單詞爲字符串，並且只得到它的第一個字符。但考慮到這樣做會從輸入緩衝區中丟棄其他字詞。