com.bigdata.bop.bindingSet

Class ListBindingSet

java.lang.Object

com.bigdata.bop.bindingSet.ListBindingSet

All Implemented Interfaces:

IBindingSet, Serializable, Cloneable

public class ListBindingSet
extends Object
implements IBindingSet

An IBindingSet based on a LinkedList. Since Vars may be compared using == this should be faster than a hash map for most operations unless the binding set has a large number of entries.

Note: #push() and #pop(boolean) are implemented by making a copy of the current symbol table with distinct Map.Entry objects. If the symbol table is saved when it is #pop(boolean) popped), then it simply replaces the pre-existing symbol table which was uncovered when it was popped off of the stack. This design has several advantages, including:

• Methods such as {@link #get(IVariable)}, {@link #set(IVariable, IConstant)}, and {@link #size()} can be written solely in terms of the current symbol table.
• {@link #clear(IVariable)} removes the {@link Map.Entry} from the current symbol table rather than introducing null values or delete markers.

The only down side to this approach is that the serialized representation of the {@link IBindingSet} is more complex. However, java default serialization will do a good job by providing back references for the object graph.

Version:

$Id: HashBindingSet.java 5123 2011-09-03 10:48:24Z thompsonbry $

Author:

Bryan Thompson

See Also:

Serialized Form

Constructor Summary

Constructors

Modifier	Constructor and Description
	ListBindingSet() Create an empty binding set.
	ListBindingSet(IVariable[] vars, IConstant[] vals) Alternative constructor.
protected	ListBindingSet(ListBindingSet src, IVariable[] variablesToKeep) Copy constructor (used by clone, copy).

Method Summary

Methods

Modifier and Type	Method and Description
void	clear(IVariable var) Clear any binding for the variable.
void	clearAll() Clear all bindings.
ListBindingSet	clone() Return a shallow copy of the binding set.
boolean	containsErrorValues()
IBindingSet	copy(IVariable[] variablesToKeep) Return a shallow copy of the binding set, eliminating unnecessary variables.
IBindingSet	copyMinusErrors(IVariable[] variablesToKeep) Return a shallow copy of the binding set, eliminating unnecessary variables and error values (equal to Constant.errorValueConstant()).
boolean	equals(Object t) True iff the variables and their bound values are the same for the two binding sets.
IConstant	get(IVariable var) Return the binding for the variable.
int	hashCode() The hash code of a binding is defined as the bit-wise XOR of the hash codes of the IConstants for its bound variables.
boolean	isBound(IVariable var) Return true iff the variable is bound.
boolean	isEmpty() true iff there are no variable bindings in the binding set.
Iterator<Map.Entry<IVariable,IConstant>>	iterator() Visits the bindings.
void	set(IVariable var, IConstant val) Bind the variable to the value.
int	size() The #of bound variables.
String	toString()
Iterator<IVariable>	vars() Visits the bound variables.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ListBindingSet

public ListBindingSet()

Create an empty binding set.

ListBindingSet

public ListBindingSet(IVariable[] vars,
              IConstant[] vals)

Alternative constructor.

Parameters:

vars - A copy is made of the data.

vals - A copy is made of the data.

ListBindingSet

protected ListBindingSet(ListBindingSet src,
              IVariable[] variablesToKeep)

Copy constructor (used by clone, copy).

Parameters:

src - The source to be copied.

variablesToKeep - The variables to be retained for the symbol table on the top of the stack (optional).

Method Detail

clone

public ListBindingSet clone()

Description copied from interface: IBindingSet

Return a shallow copy of the binding set.

Specified by:

clone in interface IBindingSet

Overrides:

clone in class Object

copy

public IBindingSet copy(IVariable[] variablesToKeep)

Description copied from interface: IBindingSet

Return a shallow copy of the binding set, eliminating unnecessary variables.

Specified by:

copy in interface IBindingSet

Parameters:

variablesToKeep - When non-null, only the listed variables are retained.

copyMinusErrors

public final IBindingSet copyMinusErrors(IVariable[] variablesToKeep)

Description copied from interface: IBindingSet

Return a shallow copy of the binding set, eliminating unnecessary variables and error values (equal to Constant.errorValueConstant()).

Specified by:

copyMinusErrors in interface IBindingSet

Parameters:

variablesToKeep - When non-null, only the listed variables are retained.

containsErrorValues

public final boolean containsErrorValues()

Specified by:

containsErrorValues in interface IBindingSet

Returns:

true if this IBindingSet contains an assignment of an error value

clear

public void clear(IVariable var)

Description copied from interface: IBindingSet

Clear any binding for the variable.

Specified by:

clear in interface IBindingSet

Parameters:

var - The variable.

clearAll

public void clearAll()

Description copied from interface: IBindingSet

Clear all bindings.

Specified by:

clearAll in interface IBindingSet

get

public IConstant get(IVariable var)

Description copied from interface: IBindingSet

Return the binding for the variable.

Specified by:

get in interface IBindingSet

Parameters:

var - The variable.

Returns:

the binding for the variable -or- null iff the variable is not bound.

isBound

public boolean isBound(IVariable var)

Description copied from interface: IBindingSet

Return true iff the variable is bound.

Specified by:

isBound in interface IBindingSet

Parameters:

var - The variable.

Returns:

true if the variable is bound.

iterator

public Iterator<Map.Entry<IVariable,IConstant>> iterator()

Description copied from interface: IBindingSet

Visits the bindings.

Specified by:

iterator in interface IBindingSet

set

public void set(IVariable var,
       IConstant val)

Description copied from interface: IBindingSet

Bind the variable to the value.

Specified by:

set in interface IBindingSet

Parameters:

var - The variable.

val - The value (MAY NOT be null).

isEmpty

public boolean isEmpty()

Description copied from interface: IBindingSet

true iff there are no variable bindings in the binding set.

Specified by:

isEmpty in interface IBindingSet

size

public int size()

Description copied from interface: IBindingSet

The #of bound variables.

Specified by:

size in interface IBindingSet

vars

public Iterator<IVariable> vars()

Description copied from interface: IBindingSet

Visits the bound variables.

Specified by:

vars in interface IBindingSet

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object t)

Description copied from interface: IBindingSet

True iff the variables and their bound values are the same for the two binding sets.

Specified by:

equals in interface IBindingSet

Overrides:

equals in class Object

Parameters:

t - Another binding set.

hashCode

public int hashCode()

Description copied from interface: IBindingSet

The hash code of a binding is defined as the bit-wise XOR of the hash codes of the IConstants for its bound variables. Unbound variables are ignored when computing the hash code. Binding sets are unordered collections, therefore the calculated hash code intentionally does not depend on the order in which the bindings are visited. The hash code reflects the current state of the bindings and must be recomputed if the bindings are changed.

Specified by:

hashCode in interface IBindingSet

Overrides:

hashCode in class Object