Expression (Apache Commons JXPath 1.4-SNAPSHOT API)

java.lang.Object
- org.apache.commons.jxpath.ri.compiler.Expression

Direct Known Subclasses:

Constant, Operation, Path, VariableReference
```
public abstract class Expression
extends Object
```
Common superclass for several types of nodes in the parse tree. Provides APIs for optimization of evaluation of expressions. Specifically, an expression only needs to executed once during the evaluation of an xpath if that expression is context-independent. Expression.isContextDependent() provides that hint.

Version:

$Revision: 652845 $ $Date: 2008-05-02 19:46:46 +0200 (Fr, 02 Mai 2008) $

Author:

Dmitri Plotnikov

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class Expression.PointerIterator
Pointer iterator

static class Expression.ValueIterator
Value Iterator

Nested Classes
Modifier and Type	Class and Description
`static class`	`Expression.PointerIterator` Pointer iterator
`static class`	`Expression.ValueIterator` Value Iterator

Field Summary

Fields
Modifier and Type Field and Description

protected static Double NOT_A_NUMBER
NaN

protected static Double ONE
one

protected static Double ZERO
zero

Fields
Modifier and Type	Field and Description
`protected static Double`	`NOT_A_NUMBER` NaN
`protected static Double`	`ONE` one
`protected static Double`	`ZERO` zero

Constructor Summary

Constructors
Constructor and Description

Expression()

Constructors
Constructor and Description
`Expression()`

Method Summary

Methods
Modifier and Type	Method and Description
`abstract Object`	`compute(EvalContext context)` Evaluates the expression.
`abstract boolean`	`computeContextDependent()` Implemented by subclasses and result is cached by isContextDependent()
`abstract Object`	`computeValue(EvalContext context)` Evaluates the expression.
`boolean`	`isContextDependent()` Returns true if this expression should be re-evaluated each time the current position in the context changes.
`Iterator`	`iterate(EvalContext context)` Iterate over the values from the specified context.
`Iterator`	`iteratePointers(EvalContext context)` Iterate over the pointers from the specified context.

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

- Field Detail
  - ZERO
```
protected static final Double ZERO
```
    zero
  - ONE
```
protected static final Double ONE
```
    one
  - NOT_A_NUMBER
```
protected static final Double NOT_A_NUMBER
```
    NaN
- Constructor Detail
  - Expression
```
public Expression()
```
- Method Detail
  - isContextDependent
```
public boolean isContextDependent()
```
    Returns true if this expression should be re-evaluated each time the current position in the context changes.
    
    Returns:
    boolean
  - computeContextDependent
```
public abstract boolean computeContextDependent()
```
    Implemented by subclasses and result is cached by isContextDependent()
    
    Returns:
    calculated context-dependentness as boolean
  - computeValue
```
public abstract Object computeValue(EvalContext context)
```
    Evaluates the expression. If the result is a node set, returns the first element of the node set.
    
    Parameters:
    context - evaluation context
    
    Returns:
    Object
  - compute
```
public abstract Object compute(EvalContext context)
```
    Evaluates the expression. If the result is a node set, returns the first element of the node set.
    
    Parameters:
    context - evaluation context
    
    Returns:
    Object
  - iterate
```
public Iterator iterate(EvalContext context)
```
    Iterate over the values from the specified context.
    
    Parameters:
    context - evaluation context
    
    Returns:
    value Iterator
  - iteratePointers
```
public Iterator iteratePointers(EvalContext context)
```
    Iterate over the pointers from the specified context.
    
    Parameters:
    context - evaluation context
    
    Returns:
    pointer Iterator

Class Expression

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

ZERO

ONE

NOT_A_NUMBER

Constructor Detail

Expression

Method Detail

isContextDependent

computeContextDependent

computeValue

compute

iterate

iteratePointers