NamespaceOperation (Java SE 15 & JDK 15) (original) (raw)

All Implemented Interfaces:

[Operation](Operation.html "interface in jdk.dynalink")

public final class NamespaceOperation extends Object implements Operation

Describes an operation that operates on at least one Namespace of an object. E.g. a property getter would be described as

Operation propertyGetter = new NamespaceOperation( StandardOperation.GET, StandardNamespace.PROPERTY);

They are often combined with NamedOperation, e.g. to express a property getter for a property named "color", you would construct:

Operation colorPropertyGetter = new NamedOperation( new NamespaceOperation( StandardOperation.GET, StandardNamespace.PROPERTY), "color");

While NamespaceOperation can be constructed directly, it is often convenient to use the Operation.withNamespace(Namespace) and Operation.withNamespaces(Namespace...) factory methods instead, e.g.:

Operation getElementOrPropertyEmpty = StandardOperation.GET .withNamespace(StandardNamespace.PROPERTY) .named("color");

Operations on multiple namespaces

If multiple namespaces are specified, the namespaces are treated as alternatives to each other in order of preference. The semantics of such operation is "first applicable". That is, a composite of GET:PROPERTY|ELEMENT:color should be interpreted as get the property named "color" on the object, but if the property does not exist, then get the collection element named "color" instead.

Operations with multiple namespaces are helpful in implementation of languages that don't distinguish between one or more of the namespaces, or when expressing operations against objects that can be considered both ordinary objects and collections, e.g. JavaMap objects. A GET:PROPERTY|ELEMENT:empty operation against a Java map will always match the Map.isEmpty() property, butGET:ELEMENT|PROPERTY:empty will actually match a map element with key "empty" if the map contains that key, and only fall back to theisEmpty() property getter if the map does not contain the key. If the source language mandates this semantics, it can be easily achieved using operations on multiple namespaces.

Even if the language itself doesn't distinguish between some of the namespaces, it can be helpful to map different syntaxes to different namespace orderings. E.g. the source expression obj.color could map toGET:PROPERTY|ELEMENT|METHOD:color, but a different source expression that looks like collection element access obj[key] could be expressed instead as GET:ELEMENT|PROPERTY|METHOD in order to favor the element semantics. Finally, if the retrieved value is subsequently called, then it makes sense to bring METHOD to the front of the namespace list: the getter part of the source expression obj.color() could beGET:METHOD|PROPERTY|ELEMENT:color and the one forobj[key]() could be GET:METHOD|ELEMENT|PROPERTY.

The base operation of a namespace operation can not itself be a namespace or named operation, but rather one of simple operations such are elements ofStandardOperation. A namespace operation itself can serve as the base operation of a named operation, though; a typical way to construct e.g. theGET:ELEMENT|PROPERTY:empty from above would be:

Operation getElementOrPropertyEmpty = StandardOperation.GET .withNamespaces( StandardNamespace.ELEMENT, StandardNamespace.PROPERTY) .named("empty");

Constructors

Constructor Description
NamespaceOperation​(Operation baseOperation,Namespace... namespaces) Constructs a new namespace operation.
Modifier and Type Method Description
boolean contains​(Namespace namespace) Returns true if this namespace operation contains a namespace equal to the specified namespace.
static boolean contains​(Operation op,Operation baseOperation,Namespace namespace) Returns true if the specified operation is a NamespaceOperation and its base operation is equal to the specified operation, and it contains the specified namespace.
boolean equals​(Object obj) Returns true if the other object is also a namespace operation and their base operation and namespaces are equal.
Operation getBaseOperation() Returns the base operation of this named operation.
static Operation getBaseOperation​(Operation op) If the passed operation is a namespace operation, returns itsgetBaseOperation(), otherwise returns the operation as is.
Namespace getNamespace​(int i) Returns the i-th namespace in this namespace operation.
int getNamespaceCount() Returns the number of namespaces in this namespace operation.
Namespace[] getNamespaces() Returns the namespaces in this namespace operation.
static Namespace[] getNamespaces​(Operation op) If the passed operation is a namespace operation, returns itsgetNamespaces(), otherwise returns an empty array.
int hashCode() Returns the hash code of this namespace operation.
String toString() Returns the string representation of this namespace operation.