What's a more concise way to do this assignment?

Question

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What's a more eloquent way to complete this assignment?
```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 mfirstLetter = fieldName.charAt(0);
    int indexOfSecondLetter;
// Checks for index of second letter
  int letterCount = 0;
  int index = 0;

while (letterCount < 2) {
    if (Character.isLetter(fieldName.charAt(index))) {
      letterCount++;
      index++;
    }
    else {
      index++;
    }
  }
  indexOfSecondLetter = index - 1;
  char mSecondLetter = fieldName.charAt(indexOfSecondLetter);

// 
if (mfirstLetter != 'm' || mSecondLetter != Character.toUpperCase(mSecondLetter)) {
  throw new IllegalArgumentException();
}
return fieldName;  
  }
}
```

Geoff Parsons · Accepted Answer

The most concise way i would jump to for solving this type of problem would be with regular expressions (https://en.wikipedia.org/wiki/Regular_expression). They're a bit out of the scope of this course but are quite useful for this type of string validation. If you're not familiar, the gist is you define a pattern using the regular expression syntax and use that to match parts of a string. Conveniently String comes with a matches method (http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#matches) that lets us match a string against a regular expression (represented as a string) and get a boolean back with very little extra work on our part.
So we'll need to define a regular expression that matches the pattern. This one should do the trick (though it's far from perfect):

^m[A-Z].*

Let's break down what that does:
The "^" matches the beginning of the line
Next we match a lowercase "m"
Next we match any uppercase letter with "[A-Z]" (note [a-z] would match all lowercase)
Finally we match any remaining characters with ".*". A period matches any character, and the asterisk means "0 or more of the previous character". 
Putting this together we can get a 3-line method that passes the challenge.
```java
public class TeacherAssistant {
  public static String validatedFieldName(String fieldName) {
    if ( !fieldName.matches("^m[A-Z].*") )
      throw new IllegalArgumentException();
    return fieldName;
  }
}
```
Again, like i said, this is a bit out of the scope for this course but you asked for concise. :)

Stephen Bone · Answer

For those not clued up with Regex like myself (yet!) here's the code I used to pass:
```java
public class TeacherAssistant {
  public static String validatedFieldName(String fieldName) {
    char firstLetter = fieldName.charAt(0);
    char secondLetter = fieldName.charAt(1);
if (firstLetter != 'm' || !Character.isUpperCase(secondLetter)) {
  throw new IllegalArgumentException();
}
return fieldName;
  }
}
```

Jess Sanders · Answer

java
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"
```java
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;
  }
}
```

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Victor Ngo

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What's a more concise way to do this assignment?

3 Answers

Geoff Parsons

Geoff Parsons

Stephen Bone

Stephen Bone

Jess Sanders

Jess Sanders