Class EmptyGreatestComparer

  • All Implemented Interfaces:
    AtomicComparer

    public class EmptyGreatestComparer
    extends java.lang.Object
    implements AtomicComparer
    A Comparer that modifies a base comparer by sorting empty key values and NaN values last (greatest), as opposed to the default which sorts them first.
    • Constructor Detail

      • EmptyGreatestComparer

        public EmptyGreatestComparer​(AtomicComparer baseComparer)
        Create an EmptyGreatestComparer
        Parameters:
        baseComparer - the comparer used to compare non-empty values (which typically sorts empty as least)
    • Method Detail

      • getBaseComparer

        public AtomicComparer getBaseComparer()
        Get the underlying comparer (which compares empty least)
        Returns:
        the base comparer
      • getCollator

        public StringCollator getCollator()
        Description copied from interface: AtomicComparer
        Get the collation used by this AtomicComparer if any
        Specified by:
        getCollator in interface AtomicComparer
        Returns:
        the collation used for comparing strings, or null if not applicable
      • provideContext

        public AtomicComparer provideContext​(XPathContext context)
        Supply the dynamic context in case this is needed for the comparison
        Specified by:
        provideContext in interface AtomicComparer
        Parameters:
        context - the dynamic evaluation context
        Returns:
        either the original AtomicComparer, or a new AtomicComparer in which the context is known. The original AtomicComparer is not modified
      • compareAtomicValues

        public int compareAtomicValues​(AtomicValue a,
                                       AtomicValue b)
                                throws NoDynamicContextException
        Compare two AtomicValue objects according to the rules for their data type. UntypedAtomic values are compared as if they were strings; if different semantics are wanted, the conversion must be done by the caller.
        Specified by:
        compareAtomicValues in interface AtomicComparer
        Parameters:
        a - the first object to be compared. It is intended that this should normally be an instance of AtomicValue, though this restriction is not enforced. If it is a StringValue, the collator is used to compare the values, otherwise the value must implement the java.util.Comparable interface.
        b - the second object to be compared. This must be comparable with the first object: for example, if one is a string, they must both be strings.
        Returns:
        <0 if a<b, 0 if a=b, >0 if a>b
        Throws:
        java.lang.ClassCastException - if the objects are not comparable
        NoDynamicContextException - if this comparer required access to dynamic context information, notably the implicit timezone, and this information is not available. In general this happens if a context-dependent comparison is attempted at compile-time, and it signals the compiler to generate code that tries again at run-time.
      • comparesEqual

        public boolean comparesEqual​(AtomicValue a,
                                     AtomicValue b)
                              throws NoDynamicContextException
        Compare two AtomicValue objects for equality according to the rules for their data type. UntypedAtomic values are compared by converting to the type of the other operand.
        Specified by:
        comparesEqual in interface AtomicComparer
        Parameters:
        a - the first object to be compared.
        b - the second object to be compared.
        Returns:
        true if the values are equal, false if not
        Throws:
        java.lang.ClassCastException - if the objects are not comparable
        NoDynamicContextException - if no dynamic context has been supplied, and a dynamic context is needed (for example, because the comparison uses the implicit timezone)
      • save

        public java.lang.String save()
        Create a string representation of this AtomicComparer that can be saved in a compiled package and used to reconstitute the AtomicComparer when the package is reloaded
        Specified by:
        save in interface AtomicComparer
        Returns:
        a string representation of the AtomicComparer