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## org.apache.xpath.compiler
Class Compiler

    java.lang.Object
      |
      +--org.apache.xpath.compiler.OpMap
            |
            +--org.apache.xpath.compiler.Compiler

public class Compiler
extends OpMap

**For advanced use only** An instance of this class compiles an XPath string expression into a Expression object. This class compiles the string into a sequence of operation codes (op map) and then builds from that into an Expression tree.

Fields inherited from class org.apache.xpath.compiler.OpMap
`MAPINDEX_LENGTH`

Constructor Summary
`Compiler()` Construct a Compiler instance that has a null error listener and a null source locator.
`Compiler(ErrorListener errorHandler, SourceLocator locator)` Construct a Compiler object with a specific ErrorListener and SourceLocator where the expression is located.

Method Summary
`void` | `assertion(boolean b, java.lang.String msg)` Tell the user of an assertion error, and probably throw an exception.
`Expression` | `compile(int opPos)` **For advanced use only** Execute the XPath object from a given opcode position.
`int` | `countPredicates(int opPos)` Count the number of predicates in the step.
`void` | `error(int msg, java.lang.Object[] args)` Tell the user of an error, and probably throw an exception.
`Expression[]` | `getCompiledPredicates(int opPos)` Compile a zero or more predicates for a given match pattern.
`int` | `getLocationPathDepth()` Get the level of the location path or union being constructed.
`PrefixResolver` | `getNamespaceContext()` Get the current namespace context for the xpath.
`int` | `getWhatToShow(int opPos)` Get a `NodeFilter` bit set that tells what to show for a given node test.
`Expression` | `locationPath(int opPos)` Compile a location path.
`Expression` | `locationPathPattern(int opPos)` Compile a location match pattern unit expression.
`Expression` | `predicate(int opPos)` Compile a location step predicate expression.
`void` | `setNamespaceContext(PrefixResolver pr)` Set the current namespace context for the xpath.
`void` | `warn(int msg, java.lang.Object[] args)` Warn the user of an problem.

Methods inherited from class org.apache.xpath.compiler.OpMap
`getArgLength, getArgLengthOfStep, getFirstChildPos, getFirstChildPosOfStep, getFirstPredicateOpPos, getNextOpPos, getNextOpPos, getNextStepPos, getOp, getOpMap, getPatternString, getStepLocalName, getStepNS, getStepTestType, getToken, getTokenQueue, getTokenQueueSize, setOp, toString`

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

Constructor Detail

### Compiler

    public Compiler(ErrorListener errorHandler,
                    SourceLocator locator)

  Construct a Compiler object with a specific ErrorListener and SourceLocator where the expression is located.
  Parameters:
    `errorHandler` - Error listener where messages will be sent, or null if messages should be sent to System err.
    `locator` - The location object where the expression lives, which may be null, but which, if not null, must be valid over the long haul, in other words, it will not be cloned.

### Compiler

    public Compiler()

  Construct a Compiler instance that has a null error listener and a null source locator.

Method Detail

### compile

    public Expression compile(int opPos)
                       throws TransformerException

  **For advanced use only** Execute the XPath object from a given opcode position.
  Parameters:
    `xctxt` - The execution context.
    `context` - The current source tree context node.
    `opPos` - The current position in the xpath.m_opMap array.
    `callback` - Interface that implements the processLocatedNode method.
    `callbackInfo` - Object that will be passed to the processLocatedNode method.
  Returns:
    The result of the XPath.
  Throws:
    TransformerException - if there is a syntax or other error.

### getLocationPathDepth

    public int getLocationPathDepth()

  Get the level of the location path or union being constructed.
  Returns:
    0 if it is a top-level path.

### locationPath

    public Expression locationPath(int opPos)
                            throws TransformerException

  Compile a location path. The LocPathIterator itself may create `AxesWalker` children.
  Parameters:
    `opPos` - The current position in the m_opMap array.
  Returns:
    reference to `LocPathIterator` instance.
  Throws:
    TransformerException - if a error occurs creating the Expression.

### predicate

    public Expression predicate(int opPos)
                         throws TransformerException

  Compile a location step predicate expression.
  Parameters:
    `opPos` - The current position in the m_opMap array.
  Returns:
    the contained predicate expression.
  Throws:
    TransformerException - if a error occurs creating the Expression.

### locationPathPattern

    public Expression locationPathPattern(int opPos)
                                   throws TransformerException

  Compile a location match pattern unit expression.
  Parameters:
    `opPos` - The current position in the m_opMap array.
  Returns:
    reference to `StepPattern` instance.
  Throws:
    TransformerException - if a error occurs creating the Expression.

### getWhatToShow

    public int getWhatToShow(int opPos)

  Get a `NodeFilter` bit set that tells what to show for a given node test.
  Parameters:
    `opPos` - the op map position for the location step.
  Returns:
    `NodeFilter` bit set that tells what to show for a given node test.

### getCompiledPredicates

    public Expression[] getCompiledPredicates(int opPos)
                                       throws TransformerException

  Compile a zero or more predicates for a given match pattern.
  Parameters:
    `opPos` - The position of the first predicate the m_opMap array.
  Returns:
    reference to array of `Expression` instances.
  Throws:
    TransformerException - if a error occurs creating the Expression.

### countPredicates

    public int countPredicates(int opPos)
                        throws TransformerException

  Count the number of predicates in the step.
  Parameters:
    `opPos` - The position of the first predicate the m_opMap array.
  Returns:
    The number of predicates for this step.
  Throws:
    TransformerException - if a error occurs creating the Expression.

### warn

    public void warn(int msg,
                     java.lang.Object[] args)
              throws TransformerException

  Warn the user of an problem.
  Parameters:
    `msg` - An error number that corresponds to one of the numbers found in `XPATHErrorResources`, which is a key for a format string.
    `args` - An array of arguments represented in the format string, which may be null.
  Throws:
    TransformerException - if the current ErrorListoner determines to throw an exception.

### assertion

    public void assertion(boolean b,
                          java.lang.String msg)

  Tell the user of an assertion error, and probably throw an exception.
  Parameters:
    `b` - If false, a runtime exception will be thrown.
    `msg` - The assertion message, which should be informative.
  Throws:
    java.lang.RuntimeException - if the b argument is false.

### error

    public void error(int msg,
                      java.lang.Object[] args)
               throws TransformerException

  Tell the user of an error, and probably throw an exception.
  Parameters:
    `msg` - An error number that corresponds to one of the numbers found in `XPATHErrorResources`, which is a key for a format string.
    `args` - An array of arguments represented in the format string, which may be null.
  Throws:
    TransformerException - if the current ErrorListoner determines to throw an exception.
  Overrides:
    error in class OpMap

### getNamespaceContext

    public PrefixResolver getNamespaceContext()

  Get the current namespace context for the xpath.
  Returns:
    The current prefix resolver, *may* be null, though hopefully not.

### setNamespaceContext

    public void setNamespaceContext(PrefixResolver pr)

  Set the current namespace context for the xpath.
  Parameters:
    `pr` - The resolver for prefixes in the XPath expression.

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