Java 字符输入验证
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Java character input validation
提问by danielG
I want to validate a single character in a java application.
I don't want the user to be able to enter a character outside the range [a - p](ignoring uppercase or lowercase) or numbers.
我想验证 Java 应用程序中的单个字符。我不希望用户能够输入范围之外的字符[a - p]（忽略大写或小写）或numbers.
Scanner input = new Scanner(System.in);
System.out.print("Choose letter in range [a - p]");
letter = input.next().charAt(0);
Any ideas?
有任何想法吗？
回答by Dyrandz Famador
you can use regexto filter input
您可以使用正则表达式来过滤输入
.matches("^[a-pA-P0-9]*$") //this will not allow outside range of [a-p A-P] or numbers
^Assert position at start of the string
^断言字符串开头的位置
-Create a character range with the adjascent tokens
-使用相邻的标记创建字符范围
a-pA single character in the range between aand p(case sensitive)
a-pa和 之间范围内的单个字符p（区分大小写）
A-PA single character in the range between Aand P(case sensitive)
A-PA和 之间范围内的单个字符P（区分大小写）
0-9A single character in the range between 0 and 9
0-90 到 9 范围内的单个字符
*Repeat previous token zeroto infinitetimes, as many times as possible
*重复前面的标识zero来infinite次，多次地
$Assert position at end of the string
$断言字符串末尾的位置
like this:
像这样：
Scanner input = new Scanner(System.in);
System.out.print("Choose letter in range [a - p]");
letter = input.next().charAt(0);
if (Character.toString(letter).matches("^[a-pA-P0-9]*$")) {
System.out.println("valid input");
}else{
System.out.println("invalid input");
}
回答by Mark
you can encapsulate it with a while loop to check if the letter is in the range or not and just keep asking the user to input a letter
你可以用while循环封装它来检查字母是否在范围内，并不断要求用户输入一个字母
do {
System.out.print("Choose letter in range [a - p]"); letter = input.next().charAt(0);
} while (letter is not in range of [a-p]); // pseudo code
回答by Shar1er80
If you're not familiar with regex, simple checks on the input can take care of it.
如果您不熟悉正则表达式，只需对输入进行简单检查即可解决。
System.out.print("Choose letter in range [a - p]");
String letter = input.nextLine();
if (letter.length() == 1 && ('a' <= letter.charAt(0) && letter.charAt(0) <= 'p')) {
System.out.println(letter);
} else {
System.out.println("Invalid input");
}
I'm using nextLine() in the event that multiple characters are accidentally entered, which is why I check that the length of letter == 1 and that the letter falls in the range that I want, otherwise it is invalid input.
如果不小心输入了多个字符，我将使用 nextLine()，这就是为什么我检查字母 == 1 的长度以及字母是否在我想要的范围内，否则就是无效输入。
