# Class AbstractOperation

Object
AbstractIdentifiedType
AbstractOperation

All Implemented Interfaces:
  `Serializable, BiFunction<AbstractFeature, ParameterValueGroup, Object>, Deprecable`

public abstract class AbstractOperation extends AbstractIdentifiedType implements BiFunction<AbstractFeature, ParameterValueGroup, Object>
Describes the behaviour of a feature type as a function or a method. Operations can:

- Compute values from the attributes.
- Perform actions that change the attribute values.

Example: a mutator operation may raise the height of a dam. This changes may affect other properties like the watercourse and the reservoir associated with the dam.
The value is computed, or the operation is executed, by `apply(Feature, ParameterValueGroup)`. If the value is modifiable, new value can be set by call to `Attribute​.setValue(Object)`.

Since:
  0.6
See Also:
  - `DefaultFeatureType`
  - Serialized Form

- ## Field Summary

  ### Fields inherited from class AbstractIdentifiedType

  `DEFINITION_KEY, DEPRECATED_KEY, DESCRIPTION_KEY, DESIGNATION_KEY, INHERIT_FROM_KEY, NAME_KEY`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `AbstractOperation(Map<String,?> identification)`
  Constructs an operation from the given properties.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract Object`
  `apply(AbstractFeature instance, ParameterValueGroup parameters)`
  Executes the operation on the specified feature with the specified parameters.
  `boolean`
  `equals(Object obj)`
  Compares this operation with the given object for equality.
  `Set<String>`
  `getDependencies()`
  Returns the names of feature properties that this operation needs for performing its task.
  `abstract ParameterDescriptorGroup`
  `getParameters()`
  Returns a description of the input parameters.
  `abstract AbstractIdentifiedType`
  `getResult()`
  Returns the expected result type.
  `int`
  `hashCode()`
  Returns a hash code value for this operation.
  `String`
  `toString()`
  Returns a string representation of this operation.
  `AbstractOperation`
  `updateDependencies(Map<String, AbstractIdentifiedType> dependencies)`
  Returns the same operation but using different properties as inputs.

  ### Methods inherited from class AbstractIdentifiedType

  `getDefinition, getDescription, getDesignation, getName, getRemarks, isDeprecated`

  ### Methods inherited from class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

  ### Methods inherited from interface BiFunction

  `andThen`

- ## Constructor Details

  - ### AbstractOperation

    public AbstractOperation(Map<String,?> identification)
    Constructs an operation from the given properties. The identification map is given unchanged to the super-class constructor. The following table is a reminder of main (not all) recognized map entries:

    Recognized map entries (non exhaustive list)
    Map key | Value type | Returned by
    --- | --- | ---
    "name" | `GenericName` or `String` | `AbstractIdentifiedType.getName()`
    "definition" | `InternationalString` or `String` | `AbstractIdentifiedType.getDefinition()`
    "designation" | `InternationalString` or `String` | `AbstractIdentifiedType.getDesignation()`
    "description" | `InternationalString` or `String` | `AbstractIdentifiedType.getDescription()`
    "deprecated" | `Boolean` | `AbstractIdentifiedType.isDeprecated()`

    Parameters:
      `identification` - the name and other information to be given to this operation.

- ## Method Details

  - ### getParameters

    public abstract ParameterDescriptorGroup getParameters()
    Returns a description of the input parameters.
    Returns:
      description of the input parameters.

  - ### getResult

    public abstract AbstractIdentifiedType getResult()
    Returns the expected result type. This type is normally not allowed to be null, but it may happen on occasion.
    Warning: In a future SIS version, the return type may be changed to `org​.opengis​.feature​.IdentifiedType`. This change is pending GeoAPI revision.
    Returns:
      the type of the result, or `null` if none.

  - ### apply

    public abstract Object apply(AbstractFeature instance, ParameterValueGroup parameters)
    Executes the operation on the specified feature with the specified parameters. The value returned by this method depends on the value returned by `getResult()`:
    - If `getResult()` returns `null`, then this method should return `null`.
    - If `getResult()` returns an instance of `AttributeType`, then this method shall return an instance of `Attribute` and the `Attribute​.getType() == getResult()` relation should hold.
    - If `getResult()` returns an instance of `FeatureAssociationRole`, then this method shall return an instance of `FeatureAssociation` and the `FeatureAssociation​.getRole() == getResult()` relation should hold.
    Analogy: if we compare `Operation` to `Method` in the Java language, then this method is equivalent to `Method​.invoke(Object, Object...)`. The `Feature` argument is equivalent to `this` in the Java language, and may be `null` if the operation does not need a feature instance (like static methods in the Java language).
    Warning: In a future SIS version, the parameter type and return value may be changed to `org​.opengis​.feature​.Feature` and `org​.opengis​.feature​.Property` respectively. This change is pending GeoAPI revision.
    Specified by:
      `apply` in interface `BiFunction<AbstractFeature, ParameterValueGroup, Object>`
    Parameters:
      `instance` - the feature instance on which to execute the operation. Can be `null` if the operation does not need feature instance.
      `parameters` - the parameters to use for executing the operation. Can be `null` if the operation does not take any parameters.
    Returns:
      the operation result, or `null` if this operation does not produce any result.

  - ### getDependencies

    public Set<String> getDependencies()
    Returns the names of feature properties that this operation needs for performing its task. This method does not resolve transitive dependencies, i.e. if a dependency is itself an operation having other dependencies, the returned set will contain the name of that operation but not the names of the dependencies of that operation (unless they are the same that the direct dependencies of `this`).

    #### Purpose

    This information is needed for writing the `SELECT` SQL statement to send to a database server. The requested columns will typically be all attributes declared in a `FeatureType`, but also any additional columns needed for the operation while not necessarily included in the `FeatureType`.

    #### Default implementation

    The default implementation returns an empty set.
    Returns:
      the names of feature properties needed by this operation for performing its task.

  - ### updateDependencies

    public AbstractOperation updateDependencies(Map<String, AbstractIdentifiedType> dependencies)
    Returns the same operation but using different properties as inputs. The keys in the given map should be values returned by `getDependencies()`, and the associated values shall be the properties to use instead of the current dependencies. If any key in the given map is not a member of the dependency set, then the entry is ignored. Conversely, if any member of the dependency set is not contained in the given map, then the associated dependency is unchanged.
    Warning: In a future SIS version, the return type may be changed to `org​.opengis​.feature​.Operation`. This change is pending GeoAPI revision.

    #### Purpose

    This method is needed by `FeatureTypeBuilder` when some properties are operations inherited from another feature type. Even if the dependencies are properties of the same name, some `characteristics` may be different. For example, the CRS may change as a result of a change of CRS.

    #### Default implementation

    The default implementation returns `this`. This is consistent with the default implementation of `getDependencies()` returning an empty set.
    Parameters:
      `dependencies` - the new properties to use as operation inputs.
    Returns:
      the new operation, or `this` if unchanged.
    Since:
      1.5
    See Also:
      - `AbstractIdentifiedType​.INHERIT_FROM_KEY`

  - ### hashCode

    public int hashCode()
    Returns a hash code value for this operation. The default implementation computes a hash code from the parameters descriptor and result type.
    Overrides:
      `hashCode` in class `AbstractIdentifiedType`
    Returns:
      the hash code for this type.

  - ### equals

    public boolean equals(Object obj)
    Compares this operation with the given object for equality. The default implementation compares the parameters descriptor and result type.
    Overrides:
      `equals` in class `AbstractIdentifiedType`
    Parameters:
      `obj` - the object to compare with this type.
    Returns:
      `true` if the given object is equal to this type.

  - ### toString

    public String toString()
    Returns a string representation of this operation. The returned string is for debugging purpose and may change in any future SIS version.
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of this operation for debugging purpose.