java - 从字符串输入中退出 While 循环

Question

所以我正在使用一个简单的 while 循环和 case 来编写一个用户菜单，但有一个问题。对于我的情况，我需要使用 char 而不是 int(为了简单起见，实际上使用字符串 Scanner)，并且在大多数情况下它都有效。但是当我输入 D (我的退出情况)时，循环不会中断。不知道为什么，我已经用 ints 做了很多次，没有出现问题......

import java.util.Scanner;

public class Postfix_Notation {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  String choice = "Z";

  while (choice != "D") {
   System.out.println("Enter A, B  or C to perform an operation or enter D to exit.");
   System.out.println("A- Evaluate a user input postfix expressions");
   System.out.println("B- Convert, display infix expressions to postfix expressions then evaluate and display the result of thepostfix expression");
   System.out.println("C- Reads words from a the text file (hangman.txt) in a LinkedList and use an iterator on it to displays all the words (duplicates allowed) in descending alphabetical order");
   System.out.println("D- Exit");
   choice = new Scanner(System.in).next();

   switch (choice) {
    case "A":
     System.out.println("Enter a string: ");
     String s = new Scanner(System.in).next();
     System.out.println("All possible permutations of " + s + " are: ");
     System.out.println("\n");
     break;

    case "B":
     Scanner input2 = new Scanner(System.in);

     System.out.println("Enter a hex string: ");
     String hexString = input2.next();

     System.out.println("The decimal equivalent of " + hexString + " is " + (hexString));
     System.out.println("\n");
     break;

    case "C":
     Scanner input = new Scanner(System.in);

     System.out.println("Enter a binary string: ");
     String binaryString = input.next();

     System.out.println("The decimal equivalent of " + binaryString + " is " + (binaryString));
     System.out.println("\n");
     break;

    case "D":

     System.out.println("Program Ended");

     break;

    default:
     System.out.println("Invalid Input");
   }
  }
 }
}

Answer 1

所以 while(!choice.equals("D")) 完成这项工作。检查此链接:How do I compare strings in Java? 。您比较的是引用而不是值。