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Java Java Objects (Retired) Delivering the MVP Validation

Charlie Gallentine
Charlie Gallentine
934 Points
Posted by Charlie Gallentine
Charlie Gallentine
934 Points

Validation throwing IllegalArgumentException

Why does mFirstName get caught on the second if block in this code? I am struggling to understand why it trips the exception.

Thank you!

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
    if (fieldName.charAt(0) != 'm') {
      throw new IllegalArgumentException("Must be m");
    }

    if (! Character.isUpperCase(fieldName.indexOf(1))) {
      throw new IllegalArgumentException("must be upper case");
    }
    return fieldName;
  }

}

2 Answers

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

Use the charAt method, not indexOf. indexOf returns the index of a specific character in the string. charAt returns the character at the specified index

We want to check if the second character in the string (index 1) is uppercase, so we call the charAt method and pass in 1 to get what that character is, then check if its uppercase

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
    if (fieldName.charAt(0) != 'm') {
      throw new IllegalArgumentException("Must be m");
    }

    // use charAt(1), not indexOf(1)
    if (!Character.isUpperCase(fieldName.charAt(1))) {
      throw new IllegalArgumentException("must be upper case");
    }
    return fieldName;
  }

}

For more information see the Java documentation

indexOf

charAt

Charlie Gallentine
Charlie Gallentine
934 Points
Charlie Gallentine
Charlie Gallentine
934 Points

Thank you! That makes perfect sense!

jacinator
jacinator
11,936 Points
jacinator
jacinator
11,936 Points

You're really close, I just did this one today, and it took me a bit. indexOf(x) returns the index of x in the string. You'll want to use charAt(x) in order to get the character.