How to check if string contains both uppercase and lowercase characters

Question

I need to validate password entered by user and check if the password contains at least one uppercase and one lowercase char in Dart.

I wrote this String extension:

extension StringValidators on String {
  bool containsUppercase() {
    // What code should be here?
  }

  bool containsLowercase() {
    // What code should be here?
  }
}

And use it like this:

final text = passwordTextController.text;
final isValid = text.containsUppercase() && text.containsLowercase();

Is there any regexp for this purpose? Or it should be plain algorithm? Please help me to find out the elegant way. Thanks!

Traverse the string character by character from start to end. Check the ASCII value of each character for the following conditions: If the ASCII value lies in the range of [65, 90], then it is an uppercase letter. If the ASCII value lies in the range of [97, 122], then it is a lowercase letter. — Truong, Jul 02 '21 at 14:18
See also this question https://stackoverflow.com/questions/40336374/how-do-i-check-if-a-java-string-contains-at-least-one-capital-letter-lowercase. It is for Java. Hope you can find an analogy in Flutter — Truong, Jul 02 '21 at 14:20
Unfortunately I don't know Dart programming language. I know Java. Anyway I guess the implementation behind ```Character.isUpperCase(ch)``` is the ASCII value as I mention in the first comment. — Truong, Jul 02 '21 at 14:27
See also this code https://www.codevscolor.com/dart-check-character-uppercase — Truong, Jul 02 '21 at 14:32

score 9 · Answer 1 · answered Jul 02 '21 at 14:26

9

Minimum 1 Upper case,
Minimum 1 lowercase,
Minimum 1 Numeric Number,
Minimum 1 Special Character,
Common Allow Character ( ! @ # $ & * ~ )

bool validateStructure(String value){
        String  pattern = r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{8,}$';
        RegExp regExp = new RegExp(pattern);
        return regExp.hasMatch(value);
  }

answered Jul 02 '21 at 14:26

S4nj33v

299
3
11

It works great but I don't need to validate all of this conditions, only lowercase and uppercase characters. Anyway thanks a lot – Mol0ko Jul 02 '21 at 14:49

score 7 · Answer 2 · answered Dec 17 '21 at 16:31

7

extension StringValidators on String {
  bool get containsUppercase => contains(RegExp(r'[A-Z]'));
  bool get containsLowercase => contains(RegExp(r'[a-z]'));
}

answered Dec 17 '21 at 16:31

Uchenna Iheanacho

126
1
4

score 2 · Accepted Answer · answered Jul 02 '21 at 14:34

For only minimum 1 upper and minimum 1 Lower only, you could use this RegEx:

RegExp regEx = new RegExp(r"(?=.*[a-z])(?=.*[A-Z])\w+");
String a = "aBc";
String b = "abc";
String c = "ABC";
print("a => " + regEx.hasMatch(a).toString());
print("b => " + regEx.hasMatch(b).toString());
print("c => " + regEx.hasMatch(c).toString());

Expected Result:

I/flutter (10220): a => true
I/flutter (10220): b => false
I/flutter (10220): c => false

Reusable

extension StringValidators on String {

  meetsPasswordRequirements() {
    RegExp regEx = new RegExp(r"(?=.*[a-z])(?=.*[A-Z])\w+");
    return regEx.hasMatch(this);
  }

}

Use

final isValid = text.meetsPasswordRequirements();

don't need the \w+ there. Once you've found the two letters, you're done. — Randal Schwartz, Jul 03 '21 at 15:57

Jamirul islam · Answer 4 · 2022-08-28T07:54:55.880

void main() {
  solve("coDE");
}

String solve(String s) {
  // your code here
  List _a = s.split("");
  String _b = "";
  List _x = [];
  List _y = [];
  for(var i in _a){
    if(i.toString() == i.toString().toUpperCase()){
      _x.add(i);
    }else{
      _y.add(i);
    }
  }
  
  if(_x.length == _y.length){
    _b = _a.join().toLowerCase();
  }else if(_x.length > _y.length){
     _b = _a.join().toUpperCase();
  }else if(_x.length < _y.length){
     _b = _a.join().toLowerCase();
  }
  return "$_b";
}

OR 

String solve2(String str) {
  return RegExp(r'[A-Z]').allMatches(str).length >
          RegExp(r'[a-z]').allMatches(str).length
      ? str.toUpperCase()
      : str.toLowerCase();
}

How to check if string contains both uppercase and lowercase characters

4 Answers4