Class ForwardingMapEntry<K extends @Nullable Object,V extends @Nullable Object>
- java.lang.Object
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- com.google.common.collect.ForwardingObject
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- com.google.common.collect.ForwardingMapEntry<K,V>
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- All Implemented Interfaces:
Map.Entry<K,V>
@GwtCompatible public abstract class ForwardingMapEntry<K extends @Nullable Object,V extends @Nullable Object> extends ForwardingObject implements Map.Entry<K,V>
A map entry which forwards all its method calls to another map entry. Subclasses should override one or more methods to modify the behavior of the backing map entry as desired per the decorator pattern.Warning: The methods of
ForwardingMapEntry
forward indiscriminately to the methods of the delegate. For example, overridinggetValue()
alone will not change the behavior ofequals(java.lang.Object)
, which can lead to unexpected behavior. In this case, you should overrideequals
as well, either providing your own implementation, or delegating to the providedstandardEquals
method.Each of the
standard
methods, where appropriate, useObjects.equal(java.lang.Object, java.lang.Object)
to test equality for both keys and values. This may not be the desired behavior for map implementations that use non-standard notions of key equality, such as the entry of aSortedMap
whose comparator is not consistent withequals
.The
standard
methods are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.- Since:
- 2.0
- Author:
- Mike Bostock, Louis Wasserman
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Constructor Summary
Constructors Modifier Constructor Description protected
ForwardingMapEntry()
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 Map.Entry<K,V>
delegate()
Returns the backing delegate instance that methods are forwarded to.boolean
equals(Object object)
Indicates whether some other object is "equal to" this one.K
getKey()
Returns the key corresponding to this entry.V
getValue()
Returns the value corresponding to this entry.int
hashCode()
Returns a hash code value for the object.V
setValue(V value)
Replaces the value corresponding to this entry with the specified value (optional operation).protected boolean
standardEquals(Object object)
protected int
standardHashCode()
protected String
standardToString()
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Methods inherited from class com.google.common.collect.ForwardingObject
toString
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Constructor Detail
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ForwardingMapEntry
protected ForwardingMapEntry()
Constructor for use by subclasses.
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Method Detail
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delegate
protected abstract Map.Entry<K,V> delegate()
Description copied from class:ForwardingObject
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.- Specified by:
delegate
in classForwardingObject
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getKey
public K getKey()
Description copied from interface:java.util.Map.Entry
Returns the key corresponding to this entry.
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getValue
public V getValue()
Description copied from interface:java.util.Map.Entry
Returns the value corresponding to this entry. If the mapping has been removed from the backing map (by the iterator'sremove
operation), the results of this call are undefined.
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setValue
public V setValue(V value)
Description copied from interface:java.util.Map.Entry
Replaces the value corresponding to this entry with the specified value (optional operation). (Writes through to the map.) The behavior of this call is undefined if the mapping has already been removed from the map (by the iterator'sremove
operation).
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equals
public boolean equals(@CheckForNull Object object)
Description copied from class:java.lang.Object
Indicates whether some other object is "equal to" this one.The
equals
method implements an equivalence relation on non-null object references:- It is reflexive: for any non-null reference value
x
,x.equals(x)
should returntrue
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified. - For any non-null reference value
x
,x.equals(null)
should returnfalse
.
The
equals
method for classObject
implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference valuesx
andy
, this method returnstrue
if and only ifx
andy
refer to the same object (x == y
has the valuetrue
).Note that it is generally necessary to override the
hashCode
method whenever this method is overridden, so as to maintain the general contract for thehashCode
method, which states that equal objects must have equal hash codes.- Specified by:
equals
in interfaceMap.Entry<K extends @Nullable Object,V extends @Nullable Object>
- Overrides:
equals
in classObject
- Parameters:
object
- the reference object with which to compare.- Returns:
true
if this object is the same as the obj argument;false
otherwise.- See Also:
Object.hashCode()
,HashMap
- It is reflexive: for any non-null reference value
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hashCode
public int hashCode()
Description copied from class:java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided byHashMap
.The general contract of
hashCode
is:- Whenever it is invoked on the same object more than once during
an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application. - If two objects are equal according to the
equals(Object)
method, then calling thehashCode
method on each of the two objects must produce the same integer result. - It is not required that if two objects are unequal
according to the
Object.equals(java.lang.Object)
method, then calling thehashCode
method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by class
Object
does return distinct integers for distinct objects. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.) - Whenever it is invoked on the same object more than once during
an execution of a Java application, the
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standardEquals
protected boolean standardEquals(@CheckForNull Object object)
A sensible definition ofequals(Object)
in terms ofgetKey()
andgetValue()
. If you override either of these methods, you may wish to overrideequals(Object)
to forward to this implementation.- Since:
- 7.0
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standardHashCode
protected int standardHashCode()
A sensible definition ofhashCode()
in terms ofgetKey()
andgetValue()
. If you override either of these methods, you may wish to overridehashCode()
to forward to this implementation.- Since:
- 7.0
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standardToString
@Beta protected String standardToString()
A sensible definition ofForwardingObject.toString()
in terms ofgetKey()
andgetValue()
. If you override either of these methods, you may wish to overrideequals(java.lang.Object)
to forward to this implementation.- Since:
- 7.0
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