I have written below regular expression in java for checking the validity of a string, but unfortunately it doesn't work.
^[a-zA-Z][a-zA-Z0-9_]
Rule:
string can be alpha numeric and _ is the only allowed special chars
string can start with only alphabets a-z or A-Z
below java code returns false even though all conditions are met.
"a1b".matches("^[a-zA-Z][a-zA-Z0-9_]")
Remove the beginning of line ^ anchor and place a quantifier after your last character class []
System.out.println("a1b".matches("[a-zA-Z][a-zA-Z0-9_]*")); // true
You could simply use..
System.out.println("a1b".matches("(?i)[a-z][a-z0-9_]*")); // true
You need to use quantifier * to make your regex match 0 or more times after first alphabet:
"a1b".matches("[a-zA-Z][a-zA-Z0-9_]*");
Or else use:
"a1b".matches("[a-zA-Z]\\w*");
PS: No need to use anchors ^ and $ in String#matches since that is already implied.
