## net.sf.saxon.instruct
Class Block

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.instruct.Instruction
              net.sf.saxon.instruct.Block

All Implemented Interfaces:
  Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfoProvider

    public class Block

extends Instruction

Implements an imaginary xsl:block instruction which simply evaluates its contents. Used for top-level templates, xsl:otherwise, etc.

See Also:
  Serialized Form

Field Summary

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

Constructor Summary
`Block()`

Method Summary
`void` `checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole)` Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
`boolean` `createsNewNodes()` Determine whether this instruction creates new nodes.
`void` `display(int level, PrintStream out, Configuration config)` Diagnostic print of expression structure.
`static void` `displayChildren(Expression[] children, int level, Configuration config, PrintStream out)` Display the children of an instruction for diagostics
`int` `getCardinality()` Determine the cardinality of the expression
`Expression[]` `getChildren()` Get the children of this instruction
`int` `getImplementationMethod()` An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
`ItemType` `getItemType(TypeHierarchy th)` Determine the data type of the items returned by this expression
`SequenceIterator` `iterate(XPathContext context)` Iterate over the results of all the child expressions
`Iterator` `iterateSubExpressions()` Get the immediate sub-expressions of this expression.
`static Expression` `makeBlock(Expression e1, Expression e2)`
`Expression` `optimize(Optimizer opt, StaticContext env, ItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
`TailCall` `processLeavingTail(XPathContext context)` ProcessLeavingTail: called to do the real work of this instruction.
`boolean` `replaceSubExpression(Expression original, Expression replacement)` Replace one subexpression by a replacement subexpression
`void` `setChildren(Expression[] children)` Set the children of this instruction
`Expression` `simplify(StaticContext env)` Simplify an expression.
`Expression` `typeCheck(StaticContext env, ItemType contextItemType)` Perform type checking of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.instruct.Instruction
`appendItem, computeCardinality, computeSpecialProperties, evaluateAsString, evaluateItem, getInstructionInfo, getInstructionNameCode, getSourceLocator, isXSLT, process, promote`

Methods inherited from class net.sf.saxon.expr.Expression

`adoptChildExpression, computeDependencies, computeStaticProperties, doPromotion, effectiveBooleanValue, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation`

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Methods inherited from interface javax.xml.transform.SourceLocator
`getColumnNumber, getLineNumber, getPublicId, getSystemId`

Constructor Detail

### Block

    public Block()

Method Detail

### makeBlock

    public static Expression makeBlock(Expression e1,
                                       Expression e2)

### setChildren

    public void setChildren(Expression[] children)

  Set the children of this instruction

  Parameters:
    `children` - The instructions that are children of this instruction

### getChildren

    public Expression[] getChildren()

  Get the children of this instruction

  Returns:
    the children of this instruction, as an array of Instruction objects. May return either a zero-length array or null if there are no children

### iterateSubExpressions

    public Iterator iterateSubExpressions()

  Description copied from class: `Expression`
  Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

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

### replaceSubExpression

    public boolean replaceSubExpression(Expression original,
                                        Expression replacement)

  Replace one subexpression by a replacement subexpression

  Specified by:
    `replaceSubExpression` in interface `Container`
  Overrides:
    `replaceSubExpression` in class `Expression`
  Parameters:
    `original` - the original subexpression
    `replacement` - the replacement subexpression
  Returns:
    true if the original subexpression is found

### getItemType

    public final ItemType getItemType(TypeHierarchy th)

  Determine the data type of the items returned by this expression

  Overrides:
    `getItemType` in class `Instruction`
  Parameters:
    `th` -
  Returns:
    the data type

### getCardinality

    public final int getCardinality()

  Determine the cardinality of the expression

  Overrides:
    `getCardinality` in class `Expression`
  Returns:
    one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

### createsNewNodes

    public final boolean createsNewNodes()

  Determine whether this instruction creates new nodes. This implementation returns true if any child instruction returns true.

  Overrides:
    `createsNewNodes` in class `Instruction`

### simplify

    public Expression simplify(StaticContext env)
                        throws XPathException

  Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

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

### typeCheck

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

  Description copied from class: `Expression`
  Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

  This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

  This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

  If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

  Overrides:
    `typeCheck` in class `Expression`
  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:
    `StaticError` - if an error is discovered during this phase (typically a type error)
    `XPathException`

### optimize

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

  Description copied from class: `Expression`
  Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

  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.

  Overrides:
    `optimize` in class `Expression`
  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`

### checkPermittedContents

    public void checkPermittedContents(SchemaType parentType,
                                       StaticContext env,
                                       boolean whole)
                                throws XPathException

  Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.

  Overrides:
    `checkPermittedContents` in class `Expression`
  Throws:
    `XPathException`

### display

    public void display(int level,
                        PrintStream out,
                        Configuration config)

  Diagnostic print of expression structure. The expression is written to the System.err output stream

  Specified by:
    `display` in class `Expression`
  Parameters:
    `level` - indentation level for this expression
    `out` -
    `config` -

### displayChildren

    public static void displayChildren(Expression[] children,
                                       int level,
                                       Configuration config,
                                       PrintStream out)

  Display the children of an instruction for diagostics

### processLeavingTail

    public TailCall processLeavingTail(XPathContext context)
                                throws XPathException

  Description copied from class: `Instruction`
  ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

  Specified by:
    `processLeavingTail` in interface `TailCallReturner`
  Specified by:
    `processLeavingTail` in class `Instruction`
  Parameters:
    `context` - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
  Returns:
    null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
  Throws:
    `XPathException`

### getImplementationMethod

    public int getImplementationMethod()

  An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively.

  Overrides:
    `getImplementationMethod` in class `Instruction`

### iterate

    public SequenceIterator iterate(XPathContext context)
                             throws XPathException

  Iterate over the results of all the child expressions

  Specified by:
    `iterate` in interface `SequenceIterable`
  Overrides:
    `iterate` in class `Instruction`
  Parameters:
    `context` - supplies the context for evaluation
  Returns:
    a SequenceIterator that can be used to iterate over the result of the expression
  Throws:
    `XPathException` - if any dynamic error occurs evaluating the expression

Copyright (C) Michael H. Kay. All rights reserved.