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Java Java Objects (Retired) Delivering the MVP Validation

Seyfullah Erdogan
Seyfullah Erdogan
1,922 Points
Posted by Seyfullah Erdogan
Seyfullah Erdogan
1,922 Points

Please help me with this 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.

The link is http://teamtreehouse.com/library/java-objects/delivering-the-mvp/validation-2

Thanks!

TeacherAssistant.java 
public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    if(! Character.isLetter("m")){
      throw new IllegalArgumentException();

    }
    // 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
    return fieldName;
  }

}

2 Answers

Chris Shaw
Chris Shaw
26,676 Points
Chris Shaw
Chris Shaw
26,676 Points

Hi Seyfullah,

Let me start of by saying I know very little about Java but I took a stab at the challenge you're working on and managed to get through it with some minor assistance from Google, below is the solution I've come up and I'll explain what's going on.

startsWithLetterM

This variable simply checks if the first character within the fieldName string is an lowercase m, if it's not it returns a boolean value of false otherwise it returns true.

secondLetterIsUppercase

secondLetterIsUppercase is a bit more tricky and I'm not even sure it's if a good way of writing it out but what I'm doing is getting the character at index one which results in the second character of the fieldName string, once I have that I'm then checking if it's an uppercase character by using Character.isUpperCase which accepts a char type which the charAt method returns to us, if the character is uppercase it returns true otherwise it returns false.

IF statement

Finally we have the IF statement which is pretty simple, all that's happening here is a check to see whether one or both sides of the equality operation equals false, if at least one of them do equal false the IllegalArgumentException is triggered otherwise the fieldName value gets returned and the code execution continues as normal.

public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    Boolean startsWithLetterM = fieldName.startsWith("m");
    Boolean secondLetterIsUppercase = Character.isUpperCase(fieldName.charAt(1));

    if (!startsWithLetterM || !secondLetterIsUppercase) {
      throw new IllegalArgumentException();
    }

    return fieldName;
  }

}

Hope that helps.

Franklin Mark Aguba
Franklin Mark Aguba
4,082 Points
Franklin Mark Aguba
Franklin Mark Aguba
4,082 Points

Thanks mate! This code saved my butt. I was struggling on it for hours. I forgot about that Character stuff that was just discussed before that quiz.

Natenda Manyau
Natenda Manyau
3,005 Points

Hi Chris in java we are told that double quotes are used for string, so why is it that we are using them on a char and surprisingly there are no syntax errors?

Chris Shaw
Chris Shaw
26,676 Points
Chris Shaw
Chris Shaw
26,676 Points

Hi Natasha,

The reason I did that is because the startsWith method doesn't have an overload for char therefore it would trigger a syntax error, the main use for the startsWith method is to match one or more characters in a string thus it's perfect for this example.

In saying that you can also compare the first character against a char as seen in the below example which would line up better with the course overall.

Boolean startsWithLetterM = fieldName.charAt(0) == 'm';

Hope that helps.

Natenda Manyau
Natenda Manyau
3,005 Points

Thank you.

i know understand

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.

  • 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"

public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {
    if (fieldName.charAt(0) != 'm' || !Character.isUpperCase(fieldName.charAt(1))) {
      throw new IllegalArgumentException("The field name does not match the style");
    }
    return fieldName;
  }

}