Initial term of field expression must be a concrete SObject error at confusing point

Question

I am writing a SObject generating class for unit test. Here is my code:

public class Uth_Integration_Obj extends Uth_Sobject
{
    public String status;
    public String sf_id;
    public String sobject_type;

    public Uth_Integration_Obj(String id)
    {
        //Default values only
        status = Integration_Status.OUTPENDING;
        sobject_type = Sobject_Type.FOLDER; //This line caused the error. 
        sf_id = id;
    }
//...

And the Sobject_Type file is a fairly simple one:

public class Sobject_Type 
{
    public final static String FOLDER = 'Folder__c';
    public final static String LISTOBJ = 'List__c';
}

I am getting the error during compilation:

Compile Error for Uth_Integration_Obj.cls: Initial term of field expression must be a concrete SObject: String at line 12 column 21

Line 12 is marked in the comment.

If I change Sobject_Type.FOLDER into 'folder__c' it will cause no issue at all. But basically they should be the same thing. I have no idea what is the issue here. Any explanation?

Answer 1

What is really happening under the hood is that you have a property named sobject_type that clashes with your class name. So when you try to reference properties on your Apex Class, it is trying to reference properties on the String class instead.

---

Your syntax is going to cause you headaches. You should also take better advantage of static types. To see why the naming is a poor choice, simply consider that SObject_Type.FOLDER would return String, while SObjectType.Folder__c would return Schema.DescribeSObjectResult and Folder__c.SObjectType would return Schema.SObjectType.

Here is how I might write the same object:

public class MyIntegrationObject
{
    public Schema.SObjectType schemaType;
    public String sf_id, status;
    public MyIntegrationObject(Id input)
    {
        if (input != null)
        {
            schemaType = input.getSObjectType();
            sf_id = input;
            status = MY_CONSTANT;
        }
    }
}

Answer 2

Making an answer as request but I feel there can be more added to it. If someone knows the WHY of it please edit the answer to include that information.

If you change the local property to sObject_Types the error goes away. Using the this keyword does not fix it either.