Module jdk.dynalink

Package jdk.dynalink

Class CompositeOperation

java.lang.Object

jdk.dynalink.CompositeOperation

All Implemented Interfaces:

Operation

public final class CompositeOperation
extends Object
implements Operation

Describes an operation that is composed of at least two other operations. The component operations are treated as alternatives to each other in order of preference. The semantics of the composite operation is "first successful". That is, a composite of GET_PROPERTY|GET_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.

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

Even if the language itself doesn't distinguish between some of the namespaces, it can be helpful to map different syntaxes to different compositions. E.g. the source expression obj.color could map to GET_PROPERTY|GET_ELEMENT|GET_METHOD:color, but a different source expression that looks like collection element access obj[key] could be expressed instead as GET_ELEMENT|GET_PROPERTY|GET_METHOD. Finally, if the retrieved value is subsequently called, then it makes sense to bring GET_METHOD to the front of the list: the getter part of the source expression obj.color() should be GET_METHOD|GET_PROPERTY|GET_ELEMENT:color and the one for obj[key]() should be GET_METHOD|GET_ELEMENT|GET_PROPERTY.

The elements of a composite operation can not be composites or named operations, but rather simple operations such are elements of StandardOperation. A composite operation itself can serve as the base operation of a named operation, though; a typical way to construct e.g. the GET_ELEMENT|GET_PROPERTY:empty from above would be:

 Operation getElementOrPropertyEmpty = new NamedOperation(
     new CompositeOperation(
         StandardOperation.GET_ELEMENT,
         StandardOperation.GET_PROPERTY),
     "empty");
 

Not all compositions make sense. Typically, any combination in any order of standard getter operations GET_PROPERTY, GET_ELEMENT, and GET_METHOD make sense, as do combinations of SET_PROPERTY and SET_ELEMENT; other standard operations should not be combined. The constructor will allow any combination of operations, though.

Constructor Summary

Constructors

Constructor and Description
CompositeOperation(Operation... operations) Constructs a new composite operation.

Method Summary

Modifier and Type	Method and Description
boolean	contains(Operation operation) Returns true if this composite operation contains an operation equal to the specified operation.
static boolean	contains(Operation composite, Operation operation) Returns true if the specified potentially composite operation is a CompositeOperation and contains an operation equal to the specified operation.
boolean	equals(Object obj) Returns true if the other object is also a composite operation and their component operations are equal.
Operation	getOperation(int i) Returns the i-th component operation in this composite operation.
int	getOperationCount() Returns the number of component operations in this composite operation.
Operation[]	getOperations() Returns the component operations in this composite operation.
static Operation[]	getOperations(Operation op) Returns the components of the passed operation if it is a composite operation, otherwise returns an array containing the operation itself.
int	hashCode() Returns the hash code of this composite operation.
String	toString() Returns the string representation of this composite operation.

Methods inherited from class java.lang.Object

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

Constructor Detail

CompositeOperation

public CompositeOperation(Operation... operations)

Constructs a new composite operation.

Parameters:

operations - the components for this composite operation. The passed array will be cloned.

Throws:

IllegalArgumentException - if less than two components are specified, or any component is itself a CompositeOperation or a NamedOperation.

NullPointerException - if either the operations array or any of its elements are null.

Method Detail

getOperations

public Operation[] getOperations()

Returns the component operations in this composite operation. The returned array is a copy and changes to it don't have effect on this object.

Returns:

the component operations in this composite operation.

getOperationCount

public int getOperationCount()

Returns the number of component operations in this composite operation.

Returns:

the number of component operations in this composite operation.

getOperation

public Operation getOperation(int i)

Returns the i-th component operation in this composite operation.

Parameters:

i - the operation index

Returns:

the i-th component operation in this composite operation.

Throws:

IndexOutOfBoundsException - if the index is out of range.

contains

public boolean contains(Operation operation)

Returns true if this composite operation contains an operation equal to the specified operation.

Parameters:

operation - the operation being searched for. Must not be null.

Returns:

true if the if this composite operation contains an operation equal to the specified operation.

equals

public boolean equals(Object obj)

Returns true if the other object is also a composite operation and their component operations are equal.

Overrides:

equals in class Object

Parameters:

obj - the object to compare to

Returns:

true if this object is equal to the other one, false otherwise.

See Also:

Object.hashCode(), HashMap

hashCode

public int hashCode()

Returns the hash code of this composite operation. Defined to be equal to java.util.Arrays.hashCode(operations).

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

toString

public String toString()

Returns the string representation of this composite operation. Defined to be the toString of its component operations, each separated by the vertical line character (e.g. "GET_PROPERTY|GET_ELEMENT").

Overrides:

toString in class Object

Returns:

the string representation of this composite operation.

getOperations

public static Operation[] getOperations(Operation op)

Returns the components of the passed operation if it is a composite operation, otherwise returns an array containing the operation itself. This allows for returning an array of component even if it is not known whether the operation is itself a composite (treating a non-composite operation as if it were a single-element composite of itself).

Parameters:

op - the operation whose components are retrieved.

Returns:

if the passed operation is a composite operation, returns its getOperations(), otherwise returns the operation itself.

contains

public static boolean contains(Operation composite,
                               Operation operation)

Returns true if the specified potentially composite operation is a CompositeOperation and contains an operation equal to the specified operation. If composite is not a CompositeOperation, then the two operations are compared for equality.

Parameters:

composite - the potentially composite operation. Must not be null.

operation - the operation being searched for. Must not be null.

Returns:

true if the if the passed operation is a CompositeOperation and contains a component operation equal to the specified operation, or if it is not a CompositeOperation and is equal to operation.