# Interfaces and Generics for a Service

Complex inheritance schemes can cause a lot of problems when two objects share a same root, but diverge too much from each other.

## Model

A model composed of:

* Interface
* JPA entity
* DTO with additional fields

```java
public interface ModelObject {

   public String getName();

   public void setName(final String name);

}

@Entity
public class ModelObjectEntity implements ModelObject {

   // Class prepared for persistence

   public Integer getId() {
      return id;
   }

}

public class ModelObjectAdditionalField implements ModelObject {

   // Implements the interface, but adds a field

   public Integer getDate() {
      return date;
   }

}
```

## Service

```java
/**
* Service making use of the interface.
* <p>
* One method expects and returns the interface.
* <p>
* Another expects and returns an iterable of the interface.
*/
public interface ModelObjectService {

   /**
   * Returns an object matching the received sample.
   *
   * @param sample the sample
   * @returns an object matching the sample
   */
   public ModelObject find(final ModelObject sample);

   /**
   * Returns an object matching the received sample.
   *
   * @param data objects to save
   * @return all the objects which could be saved
   */
   public Iterable<ModelObject> save(final Iterable<ModelObject> data);

}
```

## Usage

```java
final ModelObjectAdditionalField sample;
final ModelObject found;

sample = new ModelObjectAdditionalField();

found = service.find(sample);
```

```java
final Collection<ModelObject> data;
final Iterable<ModelObject> created;

data.add(new ModelObjectEntity());
data.add(new ModelObjectAdditionalField());

created = service.save(data);
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://bernardo.gitbook.io/development-docs/java/interfaces-and-generics-for-a-service.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.