The valid rules for defining Java identifiers are:
- It must start with either lower case alphabet[a-z] or upper case alphabet[A-Z] or underscore(_) or a dollar sign($).
- It should be a single word, the white spaces are not allowed.
- It should not start with digits.
Input: str = “$geeks123”
Explanation: The given string satisfies all the above mentioned conditions.
Input: str = “$gee ks123”
Explanation: The given string contains white spaces, therefore it is not a valid identifier.
Input: str = “1geeks$”
Explanation: The given string start with digit, therefore it is not a valid identifier.
Approach: This problem can be solved by using Regular Expression.
- Get the string.
- Create a regex to check the valid identifiers.
regex = "^([a-zA-Z_$][a-zA-Z\\d_$]*)$";
- ^ represents the starting character of the string.
- [a-zA-Z_$] represents, the string start with only lower case alphabet or upper case alphabet or underscore(_) or dollar sign($).>/li>
- [a-zA-Z\\d_$]* represents, the string can be alphanumeric or uderscore(_) or dollar sign($) after the first character of the string. It contains one or more time.
- $ represents the ending of the string.
- Match the given string with the Regex. In Java, this can be done using Pattern.matcher().
- Return true if the string matches with the given regex, else return false.
Below is the implementation of the above approach:
true false false
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