Rule Definition
Using the implementation class of a collection as the return type of your method ties your code to this specific implementation and makes it difficult to change the implementation class in the future. For example, if you use the java.util.Collection interface, you can change your implementation class from a Set to a List or to a Queue according to your needs and performance requirements.

Remediation
Declare the type as an interface of a more appropriate collection.

Violation Code Sample

/**      * @return the list of all dataset boxes present on the graphic view      */     public ArrayList<DataSetBaseBox> getDataSetBoxes()     {         ArrayList<DataSetBaseBox> dataSetBaseBoxes = new ArrayList<DataSetBaseBox>();  //VIOLATION         for (Component c : getComponents())         {             if (c instanceof DataSetBaseBox)             {                 dataSetBaseBoxes.add((DataSetBaseBox)c);             }         }         return dataSetBaseBoxes;     }

Fixed Code Sample

/**      * @return the list of all dataset boxes present on the graphic view      */     public List<DataSetBaseBox> getDataSetBoxes()     {         List<DataSetBaseBox> dataSetBaseBoxes = new List<DataSetBaseBox>();  //Fixed         for (Component c : getComponents())         {             if (c instanceof DataSetBaseBox)             {                 dataSetBaseBoxes.add((DataSetBaseBox)c);             }         }         return dataSetBaseBoxes;     }

http://java.sun.com/docs/books/tutorial/collections/interfaces/index.html https://en.wikipedia.org/wiki/Liskov_substitution_principle