Class DescendingComparer

java.lang.Object
net.sf.saxon.sort.DescendingComparer
All Implemented Interfaces:
Serializable, AtomicComparer

public class DescendingComparer extends Object implements AtomicComparer, Serializable
A Comparer used for comparing descending keys. This simply returns the inverse of the result delivered by the base comparer.
See Also:
  • Constructor Details

  • Method Details

    • getBaseComparer

      public AtomicComparer getBaseComparer()
      Get the underlying (ascending) comparer
      Returns:
      the underlying (ascending) comparer
    • 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
      Throws:
      NoDynamicContextException - if the context is an "early evaluation" (compile-time) context
    • compareAtomicValues

      public int compareAtomicValues(AtomicValue a, AtomicValue b) throws NoDynamicContextException
      Compare two objects.
      Specified by:
      compareAtomicValues in interface AtomicComparer
      Parameters:
      a - the first object to be compared. It is intended that this should 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:
      invalid input: '<'0 if ainvalid input: '<'b, 0 if a=b, >0 if a>b
      Throws:
      ClassCastException - if the objects are of the wrong type for this Comparer
      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. It is intended that this should 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 equals() method.
      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:
      true if the values are equal, false if not
      Throws:
      ClassCastException - if the objects are not comparable
      NoDynamicContextException
    • getComparisonKey

      public ComparisonKey getComparisonKey(AtomicValue a) throws NoDynamicContextException
      Get a comparison key for an object. This must satisfy the rule that if two objects are equal according to the XPath eq operator, then their comparison keys are equal according to the Java equals() method, and vice versa. There is no requirement that the comparison keys should reflect the ordering of the underlying objects.
      Specified by:
      getComparisonKey in interface AtomicComparer
      Throws:
      NoDynamicContextException