java将大写字母输入转换为特定数字

Question

我对编程非常陌生，所以我希望保持这个简单。编译器接受我的代码，但当我运行程序并键入字母A时，我只会收到大量错误。我之前尝试使用字符串字母而不是int字母，但我只是得到编译器错误，说明我无法将字符串转换为字符或其他东西。我真的很困惑，可以用一个快速的解释和修复，这样我可以得到一个数字回来。这是我的密码：

import java.util.Scanner;
import java.lang.String;

public class PhoneAlgorithm {
    public static void main(String[] args){

        int digit = -1;
        Scanner in;
        in = new Scanner(System.in);

        System.out.print("Enter an uppercase letter to find out the corresponding digit on a telephone: ");

        int letter;
        letter = Integer.parseInt(in.next());

        if (letter == 'A' || letter == 'B' || letter == 'C') {
            digit = 2;  }
        else if (letter == 'D' || letter == 'E' || letter == 'F') {
            digit = 3; }
        else if (letter == 'G' || letter == 'H' || letter == 'I') {
            digit = 4; }
        else if (letter == 'J' || letter == 'K' || letter == 'L') { 
            digit = 5; }
        else if (letter == 'M' || letter == 'N' || letter == 'O') {
            digit = 6; } 
        else if (letter == 'P' || letter == 'Q' || letter == 'R' || letter == 'S') {
            digit = 7; }
        else if (letter == 'T' || letter == 'U' || letter == 'V') {
            digit = 8; }
        else if (letter == 'W' || letter == 'X' || letter == 'Y' || letter == 'Z') {
            digit = 9; }
        else  if (letter >= 'a' && letter >= '3') {
            System.out.print("You did not enter a valid uppercase letter.  Try again!");
        }
        if (digit != -1) {
            System.out.println("The corresponding digit on your telephone is: " + digit);
        }
    }
}

Answer 1

使用parseInt(str)时，如果参数str无法转换为整数，则会得到Exception

必须使用char，因为要将输入与单个字符进行比较：

char letter;
letter = in.nextLine().charAt(0);

• str.charAt(index)返回指定索引处的字符值

Answer 2

我修改了你的代码，我想这就是你要找的

import java.util.Scanner;

public class Try {

public static void main(String[] args) {

    //declarations
    char letter;
    int digit=0;


    // Asking the user to enterstring
    System.out.println("Enter the string");
    String enterString;


    //creating a scanner object and reading the string
    Scanner input = new Scanner(System.in);  
    enterString= input.next();
    System.out.println("Entered string is "+enterString);

    int temp=0;

    for(int i=0;i<enterString.length();i++){
         letter=(char)enterString.codePointAt(i);

         if (letter == 'A' || letter == 'B' || letter == 'C') {
             digit = digit*10+2;  }
         else if (letter == 'D' || letter == 'E' || letter == 'F') {
             digit = digit*10+3; }
         else if (letter == 'G' || letter == 'H' || letter == 'I') {
             digit = digit*10+4; }
         else if (letter == 'J' || letter == 'K' || letter == 'L') { 
             digit = digit*10+5; }
         else if (letter == 'M' || letter == 'N' || letter == 'O') {
             digit = digit*10+6; } 
         else if (letter == 'P' || letter == 'Q' || letter == 'R' || letter == 'S') {
             digit = digit*10+7; }
         else if (letter == 'T' || letter == 'U' || letter == 'V') {
             digit = digit*10+8; }
         else if (letter == 'W' || letter == 'X' || letter == 'Y' || letter == 'Z') {
             digit = digit*10+9; }
         else  if (letter >= 'a' && letter >= '3') {
             System.out.print("You did not enter a valid uppercase letter.  Try again!");
         }
         /*if (digit != 0) {
             System.out.println("The corresponding digit on your telephone is: " + digit);
         }*/         
    }

    if (digit != 0) {
        System.out.println("The corresponding digit on your telephone is: " + digit);
    }

}

}