无法使用 Scanner Java 读取斜杠 ( / )

Question

I want to check if an user types a mathematical character with scanner.hasNext("[-+/*]") and it seems to not detect the "/" operation.

public void checkSign(Scanner scanner) {
        for (;!scanner.hasNext("[-+/*]");) {
                  System.err.println("You have not typed an operation (ex: + , - , * , /)!");
                  System.out.println("Try again!");
                  scanner.next();
             } 
    }

Answer 1

Slash character is identified using \\\\/ pattern

Update your pattern to [-+\\\\/*]

Answer 2

You can use the Pattern class as per below:

Pattern.matches("([/+-.*])", typed)

Here is an example:

Scanner scanner = new Scanner(System.in);
String typed = null;
while (scanner.hasNext()) {
    typed = scanner.next();
    if (Pattern.matches("([/+-.*])", typed)) {
        System.out.println("typed[/+-*]: " + typed);
    } 
}
scanner.close();   

output:

3
2
1
/
typed[/+-*]: /
*
typed[/+-*]: *
-
typed[/+-*]: -
+
typed[/+-*]: +

Answer 3

you can use \\\\ / instead of /

public void checkSign(Scanner scanner) {
        for (;!scanner.hasNext("[-+\\/*]");) {
                  System.err.println("You have not typed an operation (ex: + , - , * , /)!");
                  System.out.println("Try again!");
                  scanner.next();
             } 
    }

Answer 4

The problem was solved by not using any kind of regex but instead checking if the input is contained in the operations string like this:

public String checkSign(Scanner scanner) {  
    String line;
    scanner.nextLine();
    for (;!"+-*/".contains(line = scanner.nextLine());) {
               System.err.println("You have not typed an operand! (ex: + , - , * , /)!");
               System.out.println("Try again!");
               scanner.next();
    } 
    return line;
}