Package java.util

Interface Comparator<T>

  • public interface Comparator<T>

    • Method Detail

      • compare

        int compare​(T o1,
            T o2)
        Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

        In the foregoing description, the notation sgn(expression ) designates the mathematical signum function, which is defined to return one of -1, 0, or 1 according to whether the value of expression is negative, zero or positive.

        The implementor must ensure that sgn(compare(x, y)) == -sgn(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.)

        The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.

        Finally, the implementor must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.

        It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals."

        Parameters:
        o1 - the first object to be compared.
        o2 - the second object to be compared.
        Returns:
        a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
        Throws:
        NullPointerException - if an argument is null and this comparator does not permit null arguments
        ClassCastException - if the arguments' types prevent them from being compared by this comparator.

      • equals

        boolean equals​(@Nullable
               Object obj)
        Indicates whether some other object is "equal to" this comparator. This method must obey the general contract of Object.equals(Object). Additionally, this method can return true only if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, comp1.equals(comp2) implies that sgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2)) for every object reference o1 and o2.

        Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct comparators impose the same order.

        Overrides:
        equals in class Object
        Parameters:
        obj - the reference object with which to compare.
        Returns:
        true only if the specified object is also a comparator and it imposes the same ordering as this comparator.
        See Also:
        Object.equals(Object), Object.hashCode()