IComparator Interface

Definition

Namespace:

Java.Util

Assembly:

Mono.Android.dll

A comparison function, which imposes a total ordering on some collection of objects.

[Android.Runtime.Register("java/util/Comparator", "", "Java.Util.IComparatorInvoker")]
[Java.Interop.JavaTypeParameters(new System.String[] { "T" })]
public interface IComparator : Android.Runtime.IJavaObject, IDisposable, Java.Interop.IJavaPeerable

[<Android.Runtime.Register("java/util/Comparator", "", "Java.Util.IComparatorInvoker")>]
[<Java.Interop.JavaTypeParameters(new System.String[] { "T" })>]
type IComparator = interface
    interface IJavaObject
    interface IDisposable
    interface IJavaPeerable

Derived

Android.Content.PM.ApplicationInfo.DisplayNameComparator

Android.Content.PM.PackageItemInfo.DisplayNameComparator

Android.Content.PM.ResolveInfo.DisplayNameComparator

Android.Icu.Text.Collator

Java.Text.Collator

Attributes

RegisterAttribute JavaTypeParametersAttribute

Implements

IJavaObject IJavaPeerable IDisposable

Remarks

A comparison function, which imposes a total ordering on some collection of objects. Comparators can be passed to a sort method (such as Collections#sort(List,Comparator) Collections.sort or Arrays#sort(Object[],Comparator) Arrays.sort) to allow precise control over the sort order. Comparators can also be used to control the order of certain data structures (such as SortedSet sorted sets or SortedMap sorted maps), or to provide an ordering for collections of objects that don't have a Comparable natural ordering.

The ordering imposed by a comparator c on a set of elements S is said to be consistent with equals if and only if c.compare(e1, e2)==0 has the same boolean value as e1.equals(e2) for every e1 and e2 in S.

Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals.

For example, suppose one adds two elements a and b such that (a.equals(b) && c.compare(a, b) != 0) to an empty TreeSet with comparator c. The second add operation will return true (and the size of the tree set will increase) because a and b are not equivalent from the tree set's perspective, even though this is contrary to the specification of the Set#add Set.add method.

Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like TreeSet, TreeMap). In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.

For the mathematically inclined, the relation that defines the imposed ordering that a given comparator c imposes on a given set of objects S is:

{(x, y) such that c.compare(x, y) <= 0}.

The quotient for this total order is:

{(x, y) such that c.compare(x, y) == 0}.

It follows immediately from the contract for compare that the quotient is an equivalence relation on S, and that the imposed ordering is a total order on S. When we say that the ordering imposed by c on S is consistent with equals, we mean that the quotient for the ordering is the equivalence relation defined by the objects' Object#equals(Object) equals(Object) method(s):

{(x, y) such that x.equals(y)}.

In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same.

Unlike Comparable, a comparator may optionally permit comparison of null arguments, while maintaining the requirements for an equivalence relation.

This interface is a member of the Java Collections Framework.

Added in 1.2.

Java documentation for java.util.Comparator.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Properties

Handle	Gets the JNI value of the underlying Android object. (Inherited from IJavaObject)
JniIdentityHashCode	Returns the value of java.lang.System.identityHashCode() for the wrapped instance. (Inherited from IJavaPeerable)
JniManagedPeerState	State of the managed peer. (Inherited from IJavaPeerable)
JniPeerMembers	Member access and invocation support. (Inherited from IJavaPeerable)
PeerReference	Returns a JniObjectReference of the wrapped Java object instance. (Inherited from IJavaPeerable)

Methods

Compare(Object, Object)	Compares its two arguments for order.
Comparing(IFunction)	Accepts a function that extracts a java.lang.Comparable Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key.
Comparing(IFunction, IComparator)	Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Comparator.
ComparingDouble(IToDoubleFunction)	Accepts a function that extracts a double sort key from a type T, and returns a Comparator<T> that compares by that sort key.
ComparingInt(IToIntFunction)	Accepts a function that extracts an int sort key from a type T, and returns a Comparator<T> that compares by that sort key.
ComparingLong(IToLongFunction)	Accepts a function that extracts a long sort key from a type T, and returns a Comparator<T> that compares by that sort key.
Disposed()	Called when the instance has been disposed. (Inherited from IJavaPeerable)
DisposeUnlessReferenced()	If there are no outstanding references to this instance, then calls Dispose(); otherwise, does nothing. (Inherited from IJavaPeerable)
Equals(Object)	Indicates whether some other object is &quot;equal to&quot; this comparator.
Finalized()	Called when the instance has been finalized. (Inherited from IJavaPeerable)
NaturalOrder()	Returns a comparator that compares Comparable objects in natural order.
NullsFirst(IComparator)	Returns a null-friendly comparator that considers null to be less than non-null.
NullsLast(IComparator)	Returns a null-friendly comparator that considers null to be greater than non-null.
Reversed()	Returns a comparator that imposes the reverse ordering of this comparator.
ReverseOrder()	Returns a comparator that imposes the reverse of the <em>natural ordering</em>.
SetJniIdentityHashCode(Int32)	Set the value returned by JniIdentityHashCode. (Inherited from IJavaPeerable)
SetJniManagedPeerState(JniManagedPeerStates)	(Inherited from IJavaPeerable)
SetPeerReference(JniObjectReference)	Set the value returned by PeerReference. (Inherited from IJavaPeerable)
ThenComparing(IComparator)	Returns a lexicographic-order comparator with another comparator.
ThenComparing(IFunction)	Returns a lexicographic-order comparator with a function that extracts a Comparable sort key.
ThenComparing(IFunction, IComparator)	Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator.
ThenComparingDouble(IToDoubleFunction)	Returns a lexicographic-order comparator with a function that extracts a double sort key.
ThenComparingInt(IToIntFunction)	Returns a lexicographic-order comparator with a function that extracts an int sort key.
ThenComparingLong(IToLongFunction)	Returns a lexicographic-order comparator with a function that extracts a long sort key.
UnregisterFromRuntime()	Unregister this instance so that the runtime will not return it from future Java.Interop.JniRuntime+JniValueManager.PeekValue invocations. (Inherited from IJavaPeerable)

Extension Methods

JavaCast<TResult>(IJavaObject)	Performs an Android runtime-checked type conversion.
JavaCast<TResult>(IJavaObject)
GetJniTypeName(IJavaPeerable)