java check if char is number in switch case statment

Question

I have a switch case that checking if char is "=" or "-" or "+" but I like to check also if char is a number from 0-9

    public static Token get(char ch) {
            switch (ch) {
                case '-' :
                case '+':
                case '=':
                    return new Token(ch);
                case  Character.isDigit(ch): // this dosn't work
                {
                }
            }
        }

what can I replace the Character.isDigit with?

Does this answer your question? [What is the best way to tell if a character is a letter or number in Java without using regexes?](https://stackoverflow.com/questions/4047808/what-is-the-best-way-to-tell-if-a-character-is-a-letter-or-number-in-java-withou) — Randy Casburn, May 31 '21 at 05:10

score 2 · Answer 1 · answered May 31 '21 at 05:11

You could define explicit case statements for the ten digit characters:

public static Token get(char ch) {
    switch (ch) {
        case '-' :
        case '+':
        case '=':
            return new Token(ch);
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
            // handle digit case
            break;
    }
}

Note here that we simply let all digit characters cases flow into a single point for handling.

score 1 · Answer 2 · answered May 31 '21 at 05:22

This would not work, since a switch case compares your char ch variable to the switch cases to get a match. Character.isDigit(ch): returns a boolean value, which cannot be directly compared to char ch.

I would suggest an alternate approach where you check for your condition in the default case.

public static Token get(char ch) {
    switch (ch) {
        case '-' :
        case '+':
        case '=':
            return new Token(ch);
        default:
        if(Character.isDigit(ch){
            //enter code here
        }
    }
}

Basil Bourque · Answer 3 · 2021-05-31T06:15:13.673

The other Answers are correct and good. I would add two points:

Using a switch statement for your logic may be clouding the intent rather than clarifying it. Using a series of if-then in your particular case may make more sense.
The char type in Java is obsolete, unable to represent even half of the characters defined in Unicode. While the use of char in this particular code will work, I suggest you not make a habit of using char. Instead, learn to use code point integer numbers instead.

You can easily determine the code point.

String input = "";
int codePoint = input.codePointAt( 0 );

128567

Call Character.toString to get a String object containing a single character, the character represented by that particular code point integer number.

Example code.

public class Token
{
    public static Token get ( int codePoint )
    {
        if ( "-+=".contains( Character.toString( codePoint ) ) )
        {
            // Do operator stuff.
            return new OperatorToken( codePoint );
        } else if ( Character.isDigit( codePoint ) )
        {
            // Do digit stuff.
            return new DigitToken( codePoint );
        } else
        {
            // Do default stuff.
            return new DefaultToken( codePoint );
        }
    }
}

java check if char is number in switch case statment

3 Answers3