Package org.apache.commons.collections.comparators

Class ComparableComparator

  • All Implemented Interfaces:
    java.io.Serializable, java.util.Comparator
    public class ComparableComparator
extends java.lang.Object
implements java.util.Comparator, 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 were null, not Comparable, or for which compareTo gave inconsistent results. This is no longer the case. See compare for details.

    Since:
    Commons Collections 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
      int compare​(java.lang.Object obj1, java.lang.Object obj2)
      Compare the two Comparable arguments.
      boolean equals​(java.lang.Object object)
      Returns true iff that Object is is a Comparator whose ordering is known to be equivalent to mine.
      static ComparableComparator getInstance()
      Gets the singleton instance of a ComparableComparator.
      int hashCode()
      Implement a hash code for this comparator that is consistent with equals.

      • Methods inherited from class java.lang.Object

        getClass, notify, notifyAll, toString, wait, wait, wait

      • Methods inherited from interface java.util.Comparator

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

    • Constructor Detail

      • ComparableComparator

        public ComparableComparator()
        Constructor whose use should be avoided.

        Please use the getInstance() method whenever possible.

    • Method Detail

      • getInstance

        public static ComparableComparator getInstance()
        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.

        Returns:
        the singleton ComparableComparator

      • compare

        public int compare​(java.lang.Object obj1,
                   java.lang.Object obj2)
        Compare the two Comparable arguments. This method is equivalent to: 
        ((Comparable)obj1).compareTo(obj2)
        Specified by:
        compare in interface java.util.Comparator
        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 - when obj1 is null, or when ((Comparable)obj1).compareTo(obj2) does
        java.lang.ClassCastException - when 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 java.lang.Object
        Returns:
        a hash code for this comparator.
        Since:
        Commons Collections 3.0

      • equals

        public boolean equals​(java.lang.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 java.util.Comparator
        Overrides:
        equals in class java.lang.Object
        Parameters:
        object - the object to compare with
        Returns:
        true if equal
        Since:
        Commons Collections 3.0