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Java Java Objects (Retired) Delivering the MVP Validation

Ryan Hemrick
Ryan Hemrick
12,759 Points
Posted by Ryan Hemrick
Ryan Hemrick
12,759 Points

Validation Code Challenge

So I was wondering if you could help me with some of these code challenges. As you might've seen when a member field name doesn't match the style we've talked about, I send an error about it. Let's write some code to validate the style of the field name.

I've added the method validatedFieldName it will return the validated field name. If the value passed in doesn't meet the requirements, throw an IllegalArgumentException. I'll keep you posted on the results every time you press check work.

Not sure where to go from here. I thought that the following code would pass:

TeacherAssistant.java 
public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    // These things should be verified:
    char secondLetter = fieldName.charAt(1);
    // 1.  Member fields must start with an 'm'
    if (fieldName.charAt(0) != 'm') {
      throw new IllegalArgumentException("There was an error!");  
    }

    // 2.  The second letter in the field name must be uppercased to ensure camel-casing
    if (secondLetter != secondLetter.toUpperCase()) {
      throw new IllegalArgumentException("There was an error!"); 
    }
    // NOTE:  To check if something is not equal use the != symbol. eg: 3 != 4
    return fieldName;
  }

}

6 Answers

Axel McCode
Axel McCode
13,869 Points
Axel McCode
Axel McCode
13,869 Points

Your code/syntax are well written the problem I had with this challenge is that the program entered a value that was similar to "m_test_variable", as you can see the second character in this string is not a letter. So your if statement would validate it. To prevent the function from validating this string you need to make sure that the second character in the string is a character while also validating that it is capitalized.

Try the following code, and take a look at the second if statement to see how I went about doing this.

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("Error!");
    }
    if(!Character.isLetter(fieldName.charAt(1)) || fieldName.charAt(1) != Character.toUpperCase(fieldName.charAt(1))){
    throw new IllegalArgumentException("Error!");
    }
    return fieldName;
  }

}

The line:

!Character.isLetter(fieldName.charAt(1))

returns true, if the character at index 1 of the string "fieldName" is not a character, in which case the code would throw and IllegalArgumentException.

Hope this helps! :)

Ryan Hemrick
Ryan Hemrick
12,759 Points
Ryan Hemrick
Ryan Hemrick
12,759 Points

Thanks so much for the response and explanation. Makes sense now!

William J. Terrell
William J. Terrell
17,403 Points

So this line:

if(!Character.isLetter(fieldName.charAt(1)) || fieldName.charAt(1) != Character.toUpperCase(fieldName.charAt(1)))

checks to see if 1.) is the character at index 1 a letter, and 2.) is the character at index 1 equal to the uppercase version of itself?

Bradley Demerich
Bradley Demerich
11,688 Points
Bradley Demerich
Bradley Demerich
11,688 Points

I'm a big fan of looking for the simplest and cleanest way of writing things out. Here's what I've got, in case you are looking for any additional way of doing things:

public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {

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

      if (!Character.isLetter(fieldName.charAt(1)) || 
           !Character.isUpperCase(fieldName.charAt(1))) {
           throw new IllegalArgumentException("Second Letter must be upper Case!");
    }

      return fieldName;
  }
}

I saw you use toUpperCase in your code. Would that make the character at position 1 an upper case letter?

micram1001
micram1001
33,833 Points

Better to quote the requirements then just say error. The first letter 'm' must pass or throw an Illegal Argument Exception and the second letter must be uppercased.

Craig Dennis
STAFF
Craig Dennis
Treehouse Teacher
Craig Dennis
Craig Dennis
Treehouse Teacher

Your code looks great. This looks like the missing info you needed:

// This will return false
Character.isUpperCase('_');

char datatypes do not have a method called toUpperCase, so I assume you were getting a compiler error. Great job thinking it through!

Ryan Hemrick
Ryan Hemrick
12,759 Points
Ryan Hemrick
Ryan Hemrick
12,759 Points

Thanks for the response Craig. I've managed to get the program running a few different ways thanks to the responses here. Also want to thank you for the great Java course. You really nailed the whole object/class ideas. It is also nice to work through a project rather than reading from a textbook. This course taught me more than an entire semester of Java programming in school. Treehouse's method of teaching is outstanding. Thanks guys!

Ian Z
Ian Z
14,584 Points
Ian Z
Ian Z
14,584 Points

Craig Dennis, you have the hardest code challenges :(

Bradley Demerich
Bradley Demerich
11,688 Points

I'm glad he does. The more I have to work at figuring things out myself, the better at programing I'll become.

Justin Carothers
Justin Carothers
12,598 Points
Justin Carothers
Justin Carothers
12,598 Points

I tried to minimize everything and this worked for me. Cheers!

if ((fieldName.charAt(0) !='m') || (!Character.isUpperCase(fieldName.charAt(1)))) {

    throw new IllegalArgumentException("ILLEGAL!");

    }
Andrew Wynyard
Andrew Wynyard
3,718 Points
Andrew Wynyard
Andrew Wynyard
3,718 Points

I like this solution the best. It is much more simple than the others. I had this but separated out into two if statements. This allowed two illegal arguments for the two different issues. All of the answers above seem to be writing too much code for the problem, however I have just begun, and am probably wrong.

Otis Mason
Otis Mason
794 Points
Otis Mason
Otis Mason
794 Points

This works public static String validatedFieldName(String fieldName) {

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

if(!Character.isUpperCase(fieldName.charAt(1))) {

throw new IllegalArgumentException(" ");

} return fieldName; }

}

Jess Sanders
Jess Sanders
12,086 Points
Jess Sanders
Jess Sanders
12,086 Points 
private char validateGuess(char letter) {
    if (!Character.isLetter(letter)) {
      throw new IllegalArgumentException("A letter is required."
    }
    letter = Character.toLowerCase(letter);
    if (mMisses.indexOf(letter) >= 0 || mHits.indexOf(letter) >= 0) { 
      throw new IllegalArgumentException(letter + " has already been guessed")           }
    return letter;
  }
  • The above code is the example to follow.
  • We care about charAt for this challenge, rather than indexOf
  • In pseudocode, we want to check for the following condition, and throw an error: " if the character at index 0 of fieldName does not equal 'm' OR the character at index 1 of fieldName is not upper case"