com.icl.saxon.expr

## Class SingletonExpression

- java.lang.Object
- - com.icl.saxon.expr.Expression
  - - com.icl.saxon.expr.NodeSetExpression
    - - com.icl.saxon.expr.SingletonExpression

- Direct Known Subclasses:
    ContextNodeExpression, ParentNodeExpression, RootExpression

      public abstract class SingletonExpression
      extends NodeSetExpression

  A node set expression that will always return zero or one nodes

- - ### Field Summary

    - ### Fields inherited from class com.icl.saxon.expr.Expression

      `staticContext`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SingletonExpression()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `NodeEnumeration` | `enumerate(Context context, boolean sort)` Evaluate the expression in a given context to return a Node enumeration
    `boolean` | `evaluateAsBoolean(Context context)` Evaluate as a boolean.
    `NodeSetValue` | `evaluateAsNodeSet(Context context)` Evaluate an expression as a NodeSet.
    `java.lang.String` | `evaluateAsString(Context context)` Evaluate as a string.
    `abstract NodeInfo` | `getNode(Context context)` Get the single node to which this expression refers
    `boolean` | `isContextDocumentNodeSet()` Determine, in the case of an expression whose data type is Value.NODESET, whether all the nodes in the node-set are guaranteed to come from the same document as the context node.
    `NodeInfo` | `selectFirst(Context context)` Return the first node selected by this Expression when evaluated in the current context

    - ### Methods inherited from class com.icl.saxon.expr.NodeSetExpression

      `evaluate, getDataType, outputStringValue`

    - ### Methods inherited from class com.icl.saxon.expr.Expression

      `containsReferences, display, evaluateAsNumber, getDependencies, getStaticContext, indent, make, reduce, setStaticContext, simplify, usesCurrent`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### SingletonExpression

          public SingletonExpression()

  - ### Method Detail

    - #### isContextDocumentNodeSet

          public boolean isContextDocumentNodeSet()

      Determine, in the case of an expression whose data type is Value.NODESET, whether all the nodes in the node-set are guaranteed to come from the same document as the context node. Used for optimization.
      Overrides:
        `isContextDocumentNodeSet` in class `Expression`

    - #### getNode

          public abstract NodeInfo getNode(Context context)
                                    throws XPathException

      Get the single node to which this expression refers
      Throws:
        `XPathException`

    - #### selectFirst

          public NodeInfo selectFirst(Context context)
                               throws XPathException

      Return the first node selected by this Expression when evaluated in the current context
      Overrides:
        `selectFirst` in class `NodeSetExpression`
      Parameters:
        `context` - The context for the evaluation
      Returns:
        the NodeInfo of the first node in document order, or null if the node-set is empty.
      Throws:
        `XPathException`

    - #### enumerate

          public NodeEnumeration enumerate(Context context,
                                  boolean sort)
                                    throws XPathException

      Evaluate the expression in a given context to return a Node enumeration
      Specified by:
        `enumerate` in class `NodeSetExpression`
      Parameters:
        `context` - the evaluation context
        `sort` - Indicates result must be in document order
      Throws:
        `XPathException` - when the expression does not return a nodeset.

    - #### evaluateAsNodeSet

          public NodeSetValue evaluateAsNodeSet(Context context)
                                         throws XPathException

      Evaluate an expression as a NodeSet.
      Overrides:
        `evaluateAsNodeSet` in class `NodeSetExpression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        the value of the expression, evaluated in the current context
      Throws:
        `XPathException` - when the expression does not return a nodeset.

    - #### evaluateAsString

          public java.lang.String evaluateAsString(Context context)
                                            throws XPathException

      Evaluate as a string. Returns the string value of the node if it exists
      Overrides:
        `evaluateAsString` in class `NodeSetExpression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        true if there are any nodes selected by the NodeSetExpression
      Throws:
        `XPathException`

    - #### evaluateAsBoolean

          public boolean evaluateAsBoolean(Context context)
                                    throws XPathException

      Evaluate as a boolean. Returns true if there are any nodes selected by the NodeSetExpression
      Overrides:
        `evaluateAsBoolean` in class `NodeSetExpression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        true if there are any nodes selected by the NodeSetExpression
      Throws:
        `XPathException`