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Java Java Objects (Retired) Delivering the MVP Validation

Posted by Federico Ades
Federico Ades
934 Points

How can I verify if the first letter of a String is equal to the letter 'm'?

I eeew to verify if the first letter in a String is the letter 'm'. If it isn't, I need todo the "throw new IllegalArgumentException" to inform the user that he must start the String with an m. This is the code I made: char m_first_name = fieldName.charAt(0); if (m_first_name != 'm') { throw new IllegalArgumentException ("A letter m in Lower Case is required in the first place of the world"); }

TeacherAssistant.java 
public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    // These things should be verified:
    // 1.  Member fields must start with an 'm'
    // 2.  The second letter in the field name must be uppercased to ensure camel-casing
    // NOTE:  To check if something is not equal use the != symbol. eg: 3 != 4
    char m_first_name = fieldName.charAt(0);

    if (m_first_name != 'm') {
      throw new IllegalArgumentException ("A letter m in Lower Case is required in the first place of the world");
    }

    if (!Character.isLowerCase(fieldName.charAt(1))) {
      Character.toUpperCase(fieldName.charAt(1));
    }

    return fieldName;
  }

}

2 Answers

jcorum
jcorum
71,830 Points

You can use charAt(0) to get the first char in firstName, and Character.isUpperCase to check if the second character is upper case:

  public static String validatedFieldName(String fieldName)  {
    // These things should be verified:
    // 1.  Member fields must start with an 'm'
    // 2.  The second letter in the field name must be uppercased to ensure camel-casing
    // NOTE:  To check if something is not equal use the != symbol. eg: 3 != 4
    if (fieldName.charAt(0) != 'm' || !Character.isUpperCase(fieldName.charAt(1))) {
      throw new IllegalArgumentException();
    } else {
      return fieldName;
    }
  }
Federico Ades
Federico Ades
934 Points

Thank you very much!!

Anthony Mikhail
Anthony Mikhail
9,942 Points
Anthony Mikhail
Anthony Mikhail
9,942 Points

I believe your method should work just fine, except you aren't looping to get a proper value out. Your method tells the user their input is wrong but doesn't ask them to input a new value. You could do something like:

while (fieldName.toLowerCase().indexOf("m") != 0){ //ask the user to input a new fieldName } return fieldName;

Federico Ades
Federico Ades
934 Points

Thank you very much!!