Package org.apache.commons.collections4.comparators

Class ComparableComparator<E extends Comparable<? super E>>

java.lang.Object
org.apache.commons.collections4.comparators.ComparableComparator<E>
Type Parameters:
E - the type of objects compared by this comparator
All Implemented Interfaces:
Serializable, Comparator<E>
public class ComparableComparator<E extends Comparable<? super E>> extends Object implements Comparator<E>, Serializable
A Comparator that compares Comparable objects.

This Comparator is useful, for example, for enforcing the natural order in custom implementations of SortedSet and SortedMap.

Note: In the 2.0 and 2.1 releases of Commons Collections, this class would throw a ClassCastException if either of the arguments to compare were null, not Comparable, or for which compareTo gave inconsistent results. This is no longer the case. See compare for details.

Since:
2.0
See Also:

  • Field Details

  • Constructor Details

  • Method Details

    • comparableComparator

      public static <E extends Comparable<? super E>> ComparableComparator<E> comparableComparator()
      Gets the singleton instance of a ComparableComparator.

      Developers are encouraged to use the comparator returned from this method instead of constructing a new instance to reduce allocation and GC overhead when multiple comparable comparators may be used in the same VM.

      Type Parameters:
      E - the element type
      Returns:
      the singleton ComparableComparator
      Since:
      4.0

    • compare

      public int compare(E obj1, E obj2)
      Compare the two Comparable arguments. This method is equivalent to: 
      ((Comparable)obj1).compareTo(obj2)
      Specified by:
      compare in interface Comparator<E extends Comparable<? super E>>
      Parameters:
      obj1 - the first object to compare
      obj2 - the second object to compare
      Returns:
      negative if obj1 is less, positive if greater, zero if equal
      Throws:
      NullPointerException - if obj1 is null, or when ((Comparable)obj1).compareTo(obj2) does
      ClassCastException - if obj1 is not a Comparable, or when ((Comparable)obj1).compareTo(obj2) does

    • hashCode

      public int hashCode()
      Implement a hash code for this comparator that is consistent with equals.
      Overrides:
      hashCode in class Object
      Returns:
      a hash code for this comparator.
      Since:
      3.0

    • equals

      public boolean equals(Object object)
      Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.

      This implementation returns true iff object.getClass() equals this.getClass(). Subclasses may want to override this behavior to remain consistent with the Comparator.equals(Object) contract.

      Specified by:
      equals in interface Comparator<E extends Comparable<? super E>>
      Overrides:
      equals in class Object
      Parameters:
      object - the object to compare with
      Returns:
      true if equal
      Since:
      3.0