How can I get this switch statement to work using

问题:

I'm trying to write a program that will switch any letter of the alphabet (upper or lower cases) into the Phontic alphabet. For example, If I enter "A" or "a" my program will give me (change it to) "Alpha". I've done so much research on this and switch statements but I keep getting stuck. I've realized that I can't use 'char' in a scanner. However, when I change 'char' into a 'String' my switch statement messes up (specifically the toUpperCase in my code gets underlined. I can't see my mistake. Here's what I've done so far:

import java.util.Scanner;
public class PhoneticTranslate {
public static void main(String[] args) {


char letter;
String phonetic;

Scanner kb = new Scanner(System.in);


System.out.print("Please enter a letter: ");
letter = kb.next();

switch(Character.toUpperCase(letter))
{
case 'A':
    phonetic = "Alpha";
break;
case 'B':
    phonetic = "Bravo";
    break;
case 'C':
    phonetic = "Charlie";
    break;
case 'D': 
    phonetic = "Delta";
    break;
case 'E':
    phonetic = "Echo";
    break;
case 'F':
    phonetic = "Foxtrot";
    break;
case 'G':
    phonetic = "Golf";
    break;
case 'H':
    phonetic = "Hotel";
    break;
case 'I':
    phonetic = "India";
    break;
case 'J':
    phonetic = "Juliet";
case 'K':
    phonetic = "Kilo";
    break;
case 'L':
    phonetic = "Lima";
    break;
case 'M':
    phonetic = "Mike";
    break;
case 'N':
    phonetic = "November";
    break;
case 'O':
    phonetic = "Oscar";
    break;
case 'P':
    phonetic = "Papa";
    break;
case 'Q':
    phonetic = "Quebec";
    break;
case 'R':
    phonetic = "Romeo";
    break;
case 'S':
    phonetic = "Sierra";
    break;
case 'T':
    phonetic = "Tango";
    break;
case 'U':
    phonetic = "Uniform";
    break;
case 'V':
    phonetic = "Victor";
    break;
case 'W':
    phonetic = "Whiskey";
    break;
case 'X':
    phonetic = "X-Ray";
    break;
case 'Y':
    phonetic = "Yankee";
    break;
case 'Z':
    phonetic = "Zulu";
    break;


}

}
}

回答1:

You need to use charAt. Scanner.next() method returns String not char so you will need to convert String to char

letter = kb.next().charAt(0);

回答2:

You can better create a Map<Character, String> to save yourself from writing 26 cases in switch. This way you just have to get the String for a particular character.

Map<Character, String> mapping = new HashMap<Character, String>();
mapping.put('a', "Alpha");
mapping.put('b', "Beta");
..  And so on..

Of course you have to take the burden of initializing the Map, but it will be better than a Mess of switch - case

Benefit is that, you can also populate the Map from some file later on.

Then when you read character from scanner, use charAt(0) to fetch the first character, because Scanner.next() returns a String: -

letter = kb.next().charAt(0);

// Fetch the Phonetic for this character from `Map`
phonetic = mapping.get(letter);

回答3:

String letter;
String phonetic;
Map<String,String> codes = new HashMap<String,String>();
codes.put("A","Alpha");
codes.put("B","Bravo");
codes.put("C","Charlie");
codes.put("D","Delta");
    // not showing all assignments to make it shorter
codes.put("W","Whiskey");
codes.put("X","X-Ray");
codes.put("Y","Yankee");
codes.put("Z","Zulu");

Scanner kb = new Scanner(System.in);

System.out.print("Please enter a letter: ");
letter = kb.next().toUpperCase();

phonetic = codes.get(letter);

if (phonetic == null) {
    System.out.println("bad code : " + letter);
} else {
    System.out.println("Phonetic: " + phonetic);
}

回答4:

The Scanner.next() method returns a String, not a char, so you need to get the first character of that String using String.charAt(...) before comparing it to chars.