Question

I recently was in an interview and during that interview I realized my programming concepts aren’t as concrete as I thought.

I was asked, describe a time in your previous job where you used polymorphism?

After some thinking I said that we had a record class which every new record extended. So if we have a AddRecord or a RemoveRecord or any other type of record, they would extend Record. The record interface looked something like this:

public abstract Record{
  public writeLine(String line);
  public getColumn(int column);
  public setHeader(String header);
  ...
}

public AddRecord extends Record{
  public writeLine(String line){
      // do something
  }

  // etc...
}

public MakeRecord{
   Record r;
   public setRecord(Object s){
      if(s instanceof Record){
          r = s;
      }
   } 

   public void printNewRecord(){
      while(thingsToWrite){
          r.writeLine(something);
      }
   }
}

I just shorthanded it so don’t nit pick it please.

I told them this was using polymorphism because regardless of the record type, it could be wrote without knowing what type of record it was. This was valuable because we are writing files that needed to be padded correctly, either zero filled or padded with spaces etc…

If this isn’t polymorphism, please tell me how I can change my example into something that uses polymorphism.

Answer 1

Long answer short: yes
Polymorphism is, according to webster:a (1) : existence of a species in several forms independent of the variations of sex (2) : existence of a gene in several allelic forms (3) : existence of a molecule (as an enzyme) in several forms in a single species b : the property of crystallizing in two or more forms with distinct structure

we are focused with definition a. this describes, in java terms, as using 1 “top” class to reference two “bottom” classes. That is shown in the above example, to the best of my knowledge.