Package org.apache.commons.collections4.comparators

Class ComparableComparator<E extends java.lang.Comparable<? super E>>

  • Type Parameters:
    E - the type of objects compared by this comparator
    All Implemented Interfaces:
    java.io.Serializable, java.util.Comparator<E>
    public class ComparableComparator<E extends java.lang.Comparable<? super E>>
extends java.lang.Object
implements java.util.Comparator<E>, java.io.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(Comparable, Comparable) compare} were null, not Comparable, or for which compareTo gave inconsistent results. This is no longer the case. See compare(Comparable, Comparable) compare} for details.

    Since:
    2.0
    See Also:
    Collections.reverseOrder(), Serialized Form

    • Constructor Summary

      Constructors 
      Constructor Description
      ComparableComparator()
      Constructor whose use should be avoided.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static <E extends java.lang.Comparable<? super E>>
      ComparableComparator<E>      		 comparableComparator()
      Gets the singleton instance of a ComparableComparator.
      int compare​(E obj1, E obj2)
      Compare the two Comparable arguments.
      boolean equals​(java.lang.Object object)
      Returns true iff that Object is a Comparator whose ordering is known to be equivalent to mine.
      int hashCode()
      Implement a hash code for this comparator that is consistent with equals.

      • Methods inherited from class java.lang.Object

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

      • Methods inherited from interface java.util.Comparator

        reversed, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

    • Method Detail

      • comparableComparator

        public static <E extends java.lang.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 java.util.Comparator<E extends java.lang.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:
        java.lang.NullPointerException - if obj1 is null, or when ((Comparable)obj1).compareTo(obj2) does
        java.lang.ClassCastException - if obj1 is not a Comparable, or when ((Comparable)obj1).compareTo(obj2) does

      • equals

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

        This implementation returns true iff <em>object</em>.{@link Object#getClass() 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 java.util.Comparator<E extends java.lang.Comparable<? super E>>
        Overrides:
        equals in class java.lang.Object
        Parameters:
        object - the object to compare with
        Returns:
        true if equal
        Since:
        3.0

      • hashCode

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