爪哇中的数字转换系统

Question

import java.util.Scanner;
public class NumberConversionSystems {
    public static void main(String[] args) {
        //String binary = toBinaryString(number);
        Scanner input = new Scanner(System.in);
        System.out.println("Number Conversion Systems n");
        // Display the menu
        System.out.println("1.t Decimal to Binary");
        System.out.println("2.t Decimal to Hexadecimal");
        System.out.println("3.t Binary to Decimal");
        System.out.println("4.t Hexadecimal to Decimal n");
        System.out.println("Your choice?");
        //Get user's choice
        int choice = input.nextInt();
        switch (choice) {
            case 1: System.out.println("nEnter Decimal Number"); 
       break;
            case 2: System.out.println("nEnter Decimal Number");
                    break;
            case 3: System.out.println("nEnter Binary"); 
                    break;
            case 4: System.out.println("nEnter Hexadecimal"); 
                     break;
            default: 
                System.out.println("nInvalid choice. Please choose a number between 1 and 4.");
                choice = input.nextInt();
            break;
        }
        if (choice == 1) {
            int number = input.nextInt();
            String binary = toBinaryString(number);
            binary = recursive(number);
            System.out.printf("Decimal to Binary (%d) = %s", number, binary);   
        }
        else if (choice == 2) {
            int number2 = input.nextInt();
            String hexadecimal = toHexString(number2);
            hexadecimal = recursiveDecHex(number2);
            System.out.printf("Decimal to Hexadecimal (%d) = %s ", number2, hexadecimal);
        }
        else if (choice == 3 ) {
            String binary2 = input.next();
            int decimal = toDecimalUsingParseInt(binary2);
            decimal = recursiveBin(binary2);
            System.out.printf("n2. Binary to decimal - recursive(%s) = %d ", binary2, decimal);
        }
        else {
            String hex = input.next();
            int decimal = toHexUsingParseInt(hex);
            decimal = recursiveHexDec(hex);
            System.out.printf("Hexadecimal to Decimal (%s) = %d ", hex, decimal);   
        }
        input.close();
    }
    private static String toBinaryString(int number) {
        return Integer.toBinaryString(number);
    }
    private static String toHexString(int number) {
        return Integer.toHexString(number);
    }
    private static int toDecimalUsingParseInt(String binaryNumber) {
        return Integer.parseInt(binaryNumber, 2);
    }
    private static int toHexUsingParseInt(String number) {
        return Integer.parseInt(number, 16);
    }
    private static String recursive(int number) {
        StringBuilder builder = new StringBuilder();
        if (number > 0) {
            String binaryNumber = recursive(number / 2);
            int digit = number % 2;
            builder.append(binaryNumber + digit);
        }
        return builder.toString();
    }
    private static String recursiveDecHex(int number) {
        StringBuilder builder = new StringBuilder();
        if (number > 0) {
            String hexNumber = recursiveDecHex(number / 16);
            String hexCode = "0123456789ABCDEF";
            int hexDigit = number % 16;
            builder.append(hexNumber + hexCode.charAt(hexDigit));
        }
        return builder.toString();
    }
    private static int recursiveBin(String binaryNumber) {
        int decimal = 0;
        int length = binaryNumber.length();
        if (length > 0) {
            String substring = binaryNumber.substring(1);
            int digit = Character.getNumericValue(binaryNumber.charAt(0));
            decimal = digit * (int) Math.pow(2, length - 1) + recursiveBin(substring);
        }
        return decimal;
    }
    private static int recursiveHexDec(String hexNumber) {
        int decimal = 0;
        String hexCode = "0123456789ABCDEF";
        hexNumber = hexNumber.toUpperCase();
        int length = hexNumber.length();
        if (length > 0) {
            char ch = hexNumber.charAt(0);
            int digit = hexCode.indexOf(ch);
            String substring = hexNumber.substring(1);
            decimal = digit * (int) Math.pow(16, length - 1) + recursiveHexDec(substring);
        }
        return decimal;
    }
    }

当我选择一个无效的数字（不在1和4之间的数字）时，程序将显示"无效的选择。请选择一个介于 1 和 4 之间的数字，当我在此之后输入有效数字时，程序将停止运行。

例如，如果我

选择"1"，它不会要求我输入十进制数。我错过了什么？

Answer 1

您没有循环，您一次又一次地尝试它，直到输入一个有效的数字。

试试这个：

int choice = -1;
        while (choice < 0 || choice > 4) {
            choice = input.nextInt();
            switch (choice) {
                case 1:
                    System.out.println("nEnter Decimal Number");
                    break;
                case 2:
                    System.out.println("nEnter Decimal Number");
                    break;
                case 3:
                    System.out.println("nEnter Binary");
                    break;
                case 4:
                    System.out.println("nEnter Hexadecimal");
                    break;
                default:
                    System.out.println("nInvalid choice. Please choose a number between 1 and 4.");
                    break;
            }
        }

但请记住，输入正确数字旁边的循环无法逃脱。

Answer 2

您正在等待交换机默认值中的新条目。 所以它只是坐在那里，直到你把一个放进去。

您可以在切换之前更轻松地完成该部分：

boolean badEntry = true;
    do{
    System.out.println("Your choice?");
    int choice = input.nextInt();
    if (( choice<1 )|| (choice>4)) {
      System.out.println("nInvalid choice. Please choose a number between 1 and 4.");
    } else {
      badEntry = false;
    }
      }
    while (badEntry);

Answer 3

您的程序不会停止。 它实际上是在您输入有效数字后等待输入。 如果您不相信我，请在输入有效选项后尝试输入另一个数字。 对我来说，它的工作原理是这样的。

Number Conversion Systems 
1.   Decimal to Binary
2.   Decimal to Hexadecimal
3.   Binary to Decimal
4.   Hexadecimal to Decimal 
Your choice?
5
Invalid choice. Please choose a number between 1 and 4.
1
23
Decimal to Binary (23) = 10111

但是，当您到达程序中输入有效选项的点时，打印出消息（如"输入十进制数"）的部分已经过去;这就是您没有收到该消息的原因。