Class ForwardingObject
- java.lang.Object
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- com.google.common.collect.ForwardingObject
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- Direct Known Subclasses:
ForwardingCache
,ForwardingCollection
,ForwardingExecutorService
,ForwardingFuture
,ForwardingIterator
,ForwardingMap
,ForwardingMapEntry
,ForwardingMultimap
,ForwardingTable
@GwtCompatible public abstract class ForwardingObject extends java.lang.Object
An abstract base class for implementing the decorator pattern. Thedelegate()
method must be overridden to return the instance being decorated.This class does not forward the
hashCode
andequals
methods through to the backing object, but relies onObject
's implementation. This is necessary to preserve the symmetry ofequals
. Custom definitions of equality are usually based on an interface, such asSet
orList
, so that the implementation ofequals
can cast the object being tested for equality to the custom interface.ForwardingObject
implements no such custom interfaces directly; they are implemented only in subclasses. Therefore, forwardingequals
would break symmetry, as the forwarding object might consider itself equal to the object being tested, but the reverse could not be true. This behavior is consistent with the JDK's collection wrappers, such asCollections.unmodifiableCollection(java.util.Collection<? extends T>)
. Use an interface-specific subclass ofForwardingObject
, such asForwardingList
, to preserve equality behavior, or overrideequals
directly.The
toString
method is forwarded to the delegate. Although this class does not implementSerializable
, a serializable subclass may be created since this class has a parameter-less constructor.- Since:
- 2.0
- Author:
- Mike Bostock
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Constructor Summary
Constructors Modifier Constructor Description protected
ForwardingObject()
Constructor for use by subclasses.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description protected abstract java.lang.Object
delegate()
Returns the backing delegate instance that methods are forwarded to.java.lang.String
toString()
Returns the string representation generated by the delegate'stoString
method.
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Constructor Detail
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ForwardingObject
protected ForwardingObject()
Constructor for use by subclasses.
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Method Detail
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delegate
protected abstract java.lang.Object delegate()
Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such asForwardingSet.delegate()
. Concrete subclasses override this method to supply the instance being decorated.
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toString
public java.lang.String toString()
Returns the string representation generated by the delegate'stoString
method.- Overrides:
toString
in classjava.lang.Object
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