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## net.sf.saxon.expr
Class UnaryExpression

    java.lang.Object
      net.sf.saxon.expr.ComputedExpression
          net.sf.saxon.expr.UnaryExpression

All Implemented Interfaces:
  Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

Direct Known Subclasses:
  AtomicSequenceConverter, Atomizer, CardinalityChecker, CastableExpression, CastExpression, DocumentSorter, FirstItemExpression, InstanceOfExpression, ItemChecker, LazyExpression, NumericPromoter, Reverser, SingletonAtomizer, StringMirrorExpression, UntypedAtomicConverter

public abstract class UnaryExpression
extends ComputedExpression

Unary Expression: an expression taking a single operand expression

See Also:
  Serialized Form

Field Summary
`protected Expression` | `operand`

Fields inherited from class net.sf.saxon.expr.ComputedExpression
`locationId, staticProperties`

Fields inherited from interface net.sf.saxon.expr.Expression
`EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD`

Constructor Summary
`UnaryExpression(Expression p0)`

Method Summary
`int` | `computeCardinality()` Determine the static cardinality.
`int` | `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`void` | `display(int level, NamePool pool, java.io.PrintStream out)` Diagnostic print of expression structure
`protected abstract java.lang.String` | `displayOperator(NamePool pool)` Give a string representation of the operator for use in diagnostics
`boolean` | `equals(java.lang.Object other)` Is this expression the same as another expression?
`Expression` | `getBaseExpression()`
`ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the expression, if possible.
`int` | `hashCode()` get HashCode for comparing two expressions.
`java.util.Iterator` | `iterateSubExpressions()` Get the immediate subexpressions of this expression
`Expression` | `optimize(Optimizer opt, StaticContext env, ItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
`Expression` | `promote(PromotionOffer offer)` Promote this expression if possible
`Expression` | `simplify(StaticContext env)` Simplify an expression
`Expression` | `typeCheck(StaticContext env, ItemType contextItemType)` Type-check the expression.

Methods inherited from class net.sf.saxon.expr.ComputedExpression
`adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### operand

    protected Expression operand

Constructor Detail

### UnaryExpression

    public UnaryExpression(Expression p0)

Method Detail

### getBaseExpression

    public Expression getBaseExpression()

### simplify

    public Expression simplify(StaticContext env)
                        throws XPathException

  Simplify an expression

  Specified by:
    `simplify` in interface `Expression`
  Overrides:
    `simplify` in class `ComputedExpression`
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### typeCheck

    public Expression typeCheck(StaticContext env,
                                ItemType contextItemType)
                         throws XPathException

  Type-check the expression. Default implementation for unary operators that accept any kind of operand

  Parameters:
    `env` - the static context of the expression
    `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
  Returns:
    the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
  Throws:
    `XPathException`

### optimize

    public Expression optimize(Optimizer opt,
                               StaticContext env,
                               ItemType contextItemType)
                        throws XPathException

  Perform optimisation of an expression and its subexpressions.

  This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

  Parameters:
    `opt` - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
    `env` - the static context of the expression
    `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
  Returns:
    the original expression, rewritten if appropriate to optimize execution
  Throws:
    `StaticError` - if an error is discovered during this phase (typically a type error)
    `XPathException`

### promote

    public Expression promote(PromotionOffer offer)
                       throws XPathException

  Promote this expression if possible

  Specified by:
    `promote` in interface `Expression`
  Overrides:
    `promote` in class `ComputedExpression`
  Parameters:
    `offer` - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
  Returns:
    if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
  Throws:
    `XPathException` - if any error is detected

### iterateSubExpressions

    public java.util.Iterator iterateSubExpressions()

  Get the immediate subexpressions of this expression

  Specified by:
    `iterateSubExpressions` in interface `Expression`
  Overrides:
    `iterateSubExpressions` in class `ComputedExpression`
  Returns:
    an iterator containing the sub-expressions of this expression

### computeSpecialProperties

    public int computeSpecialProperties()

  Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

  Overrides:
    `computeSpecialProperties` in class `ComputedExpression`

### computeCardinality

    public int computeCardinality()

  Determine the static cardinality. Default implementation returns the cardinality of the operand

  Specified by:
    `computeCardinality` in class `ComputedExpression`

### getItemType

    public ItemType getItemType(TypeHierarchy th)

  Determine the data type of the expression, if possible. The default implementation for unary expressions returns the item type of the operand

  Parameters:
    `th` -
  Returns:
    the item type of the items in the result sequence, insofar as this is known statically.

### equals

    public boolean equals(java.lang.Object other)

  Is this expression the same as another expression?

### hashCode

    public int hashCode()

  get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

### display

    public void display(int level,
                        NamePool pool,
                        java.io.PrintStream out)

  Diagnostic print of expression structure

  Parameters:
    `level` - indentation level for this expression
    `pool` - NamePool used to expand any names appearing in the expression
    `out` - Output destination

### displayOperator

    protected abstract java.lang.String displayOperator(NamePool pool)

  Give a string representation of the operator for use in diagnostics

  Returns:
    the operator, as a string

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