Check whether the given string is a valid identifier | Java implementation of the approach ; Function that returns true if str is a valid identifier ; If first character is invalid ; Traverse the string for the rest of the characters ; String is a valid identifier ; Driver code
import java . util . * ; class GFG { static boolean isValid ( String str , int n ) { if ( ! ( ( str . charAt ( 0 ) >= ' a ' && str . charAt ( 0 ) <= ' z ' ) || ( str . charAt ( 0 ) >= ' A ' && str . charAt ( 0 ) <= ' Z ' ) || str . charAt ( 0 ) == ' _ ' ) ) return false ; for ( int i = 1 ; i < str . length ( ) ; i ++ ) { if ( ! ( ( str . charAt ( i ) >= ' a ' && str . charAt ( i ) <= ' z ' ) || ( str . charAt ( i ) >= ' A ' && str . charAt ( i ) <= ' Z ' ) || ( str . charAt ( i ) >= '0' && str . charAt ( i ) <= '9' ) || str . charAt ( i ) == ' _ ' ) ) return false ; } return true ; } public static void main ( String args [ ] ) { String str = " _ geeks123" ; int n = str . length ( ) ; if ( isValid ( str , n ) ) System . out . println ( " Valid " ) ; else System . out . println ( " Invalid " ) ; } }