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Java Java Objects (Retired) Delivering the MVP Validation

Posted by Carter Pringle
Carter Pringle
3,416 Points

Stuck on Stage 4 exercise

The wording is a little weird, for me, so I don't really know what needs to be done?

"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."

3 Answers

Allan Clark
Allan Clark
10,810 Points
Allan Clark
Allan Clark
10,810 Points

The comments inside the code help a lot: // 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

Basically the method will be passed a String in the argument fieldName. You need to add code to make sure that String meets the 2 above requirements, throw an exception if the String does not meet them.

Carter Pringle
Carter Pringle
3,416 Points

Shouldn't this work? It's giving me an error

public class TeacherAssistant {

  public static String validatedFieldName(String fieldName) {

    try{
    if (fieldName.startsWith("m")){
      if (Character.isUpperCase(fieldName.charAt(1))){
       System.out.println("Is good"); 
        return fieldName;
      }
    } 
    } catch (IllegalArgumentException iae){

    }
    return null;
    // 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

  }

}
Allan Clark
Allan Clark
10,810 Points
Allan Clark
Allan Clark
10,810 Points 
if (fieldName.startsWith("m")){

Field name is a String, it does not come with a startsWith() method. You could create your own private method that would do this but String comes with a way of accessing individual characters with the charAt() method. Using charAt() should save you writing the extra method lines.

Carter Pringle
Carter Pringle
3,416 Points
Carter Pringle
Carter Pringle
3,416 Points

Ok, every couple of days I give this thing another shot, and it's frustrating how one little exercise is holding me back. Anway I can get a 'by'?

Allan Clark
Allan Clark
10,810 Points
Allan Clark
Allan Clark
10,810 Points 
if (fieldName.startsWith("m")){

The starsWith() method isn't on the String API:

http://docs.oracle.com/javase/7/docs/api/java/lang/String.html

To check the first letter is an m you would need to use the charAt() method and logical operators. Remember the it is 0 indexed so the first letter in the String is at 0. Replace the above code with this:

if(fieldName.charAt(0) == 'm') {

This grabs the first letter of the string as a char so you can compare it directly to the 'm' char.