java 如何使用扫描仪使这个 switch 语句起作用？
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How can I get this switch statement to work using a scanner?
提问by user1753668
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 toUpperCasein my code gets underlined. I can't see my mistake. Here's what I've done so far:
我正在尝试编写一个程序，可以将字母表中的任何字母（大写或小写）转换为 Phontic 字母表。例如，如果我输入“A”或“a”，我的程序会给我（将其更改为）“Alpha”。我对这个和 switch 语句做了很多研究，但我一直被卡住。我意识到我不能在扫描仪中使用“char”。但是，当我将 'char' 更改为 'String' 时，我的 switch 语句搞砸了（特别是我代码中的toUpperCase带有下划线。我看不出我的错误。这是我到目前为止所做的：
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by Amit Deshpande
You need to use charAt. Scanner.next()method returns Stringnot charso you will need to convert Stringto char
您需要使用 charAt。Scanner.next()方法String不返回char所以你需要转换String为char
letter = kb.next().charAt(0);
回答by Rohit Jain
You can better create a Map<Character, String>to save yourself from writing 26 casesin switch. This way you just have to getthe String for a particular character.
您可以更好地创建一个Map<Character, String>以防止自己26 cases在 switch 中写入。这样你只需要get为一个特定的字符字符串。
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 Messof switch - case
当然，你必须要初始化的负担Map，但它会比一个更好Mess的switch - case
Benefit is that, you can also populatethe Mapfrom some filelater on.
好处是，你还可以populate将Map一些file以后。
Then when you read character from scanner, use charAt(0)to fetch the first character, because Scanner.next()returns a String: -
然后当您从扫描仪读取字符时，用于charAt(0)获取第一个字符，因为Scanner.next()返回一个字符串：-
letter = kb.next().charAt(0);
// Fetch the Phonetic for this character from `Map`
phonetic = mapping.get(letter);
回答by Tulains Córdova
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by Richard JP Le Guen
The Scanner.next()methodreturns a String, not a char, so you need to get the first character of that Stringusing String.charAt(...)before comparing it to chars.
该Scanner.next()方法返回 a String，而不是 a char，因此您需要在将其与s进行比较之前获取Stringusing的第一个字符。String.charAt(...)char
