Package net.sf.saxon.expr.sort
Class DescendingComparer
- java.lang.Object
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- net.sf.saxon.expr.sort.DescendingComparer
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- All Implemented Interfaces:
java.io.Serializable
,AtomicComparer
public class DescendingComparer extends java.lang.Object implements AtomicComparer, java.io.Serializable
A Comparer used for comparing descending keys. This simply returns the inverse of the result delivered by the base comparer.- See Also:
- Serialized Form
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Constructor Summary
Constructors Constructor Description DescendingComparer(AtomicComparer base)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
compareAtomicValues(AtomicValue a, AtomicValue b)
Compare two objects.boolean
comparesEqual(AtomicValue a, AtomicValue b)
Compare two AtomicValue objects for equality according to the rules for their data type.AtomicComparer
getBaseComparer()
Get the underlying (ascending) comparerStringCollator
getCollator()
Get the collation used by this AtomicComparer if anyComparisonKey
getComparisonKey(AtomicValue a)
Get a comparison key for an object.AtomicComparer
provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison
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Constructor Detail
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DescendingComparer
public DescendingComparer(AtomicComparer base)
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Method Detail
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getBaseComparer
public AtomicComparer getBaseComparer()
Get the underlying (ascending) comparer- Returns:
- the underlying (ascending) comparer
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getCollator
public StringCollator getCollator()
Description copied from interface:AtomicComparer
Get the collation used by this AtomicComparer if any- Specified by:
getCollator
in interfaceAtomicComparer
- Returns:
- the collation used for comparing strings, or null if not applicable
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provideContext
public AtomicComparer provideContext(XPathContext context)
Supply the dynamic context in case this is needed for the comparison- Specified by:
provideContext
in interfaceAtomicComparer
- 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
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compareAtomicValues
public int compareAtomicValues(AtomicValue a, AtomicValue b) throws NoDynamicContextException
Compare two objects.- Specified by:
compareAtomicValues
in interfaceAtomicComparer
- 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:
- <0 if a0 if a>b
- Throws:
java.lang.ClassCastException
- if the objects are of the wrong type for this ComparerNoDynamicContextException
- 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.
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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 interfaceAtomicComparer
- 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:
java.lang.ClassCastException
- if the objects are not comparableNoDynamicContextException
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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 interfaceAtomicComparer
- Throws:
NoDynamicContextException
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