com.bigdata.bop.Constant Maven / Gradle / Ivy
/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
[email protected]
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package com.bigdata.bop;
import java.util.Collections;
/**
* A constant.
*
* @author Bryan Thompson
* @version $Id$
*/
final public class Constant extends ImmutableBOp implements IConstant {
/**
*
*/
private static final long serialVersionUID = -2967861242470442497L;
final private E value;
public interface Annotations extends ImmutableBOp.Annotations {
/**
* The {@link IVariable} which is bound to that constant value
* (optional).
*
* {@link BOpContext#bind(IPredicate, IConstraint[], Object, IBindingSet)}
* takes care of propagating the binding onto the variable for solutions
* which join.
*
* Note: The {@link Var} class in bigdata provides a guarantee of
* reference testing for equality, which is why we can not simply attach
* the constant to the variable and have the variable report its bound
* value. *
*/
String VAR = Constant.class.getName() + ".var";
}
final public boolean isVar() {
return false;
}
final public boolean isConstant() {
return true;
}
// /**
// * Required shallow copy constructor.
// *
// * @param op
// */
// public Constant(final BOp[] args, final Map ann) {
// super(args,ann);
// this.value = null;
// }
/**
* Constructor required for {@link com.bigdata.bop.BOpUtility#deepCopy(FilterNode)}.
*
* @param op
*/
public Constant(final Constant op) {
super(op);
this.value = op.value;
}
/**
* Create a constant which models a variable bound to that constant. This
* may be used when a variable has an external binding, such as when a
* single binding set is provided as input to a query. By pairing the
* {@link Constant} with the {@link IVariable} and handling this case when
* solutions are joined the resulting solutions will have the variable with
* its constant bound value.
*
* Note: The {@link Var} class in bigdata provides a guarantee of reference
* testing for equality, which is why we can not simply attach the constant
* to the variable and have the variable report its bound value. *
*
* Note: A very similar effect may be achieved by simply binding the
* variable on the {@link IBindingSet} to the constant. However, there are
* some (few) cases where we can not do that because the binding must be
* applied for all solutions and we lack access to the input solutions.
*
* See
* {@link BOpContext#bind(IPredicate, IConstraint[], Object, IBindingSet)},
* which takes care of propagating the binding onto the variable for
* solutions which join.
*
* @param var
* The variable.
* @param value
* The bound value.
*/
public Constant(final IVariable var, final E value) {
super(BOp.NOARGS, Collections.singletonMap(Annotations.VAR,
(Object) var));
// NV.asMap(new NV(Annotations.VAR, var)));
if (var == null)
throw new IllegalArgumentException();
if (value == null)
throw new IllegalArgumentException();
if(value instanceof IConstant) {
// Recursive nesting of Constant is not allowed.
throw new IllegalArgumentException();
}
this.value = value;
}
/**
* Create a constant for the value.
*
* @param value
* The value (may not be null).
*/
public Constant(final E value) {
super(BOp.NOARGS, BOp.NOANNS);
if (value == null)
throw new IllegalArgumentException();
if(value instanceof IConstant) {
// Recursive nesting of Constant is not allowed.
throw new IllegalArgumentException();
}
this.value = value;
}
/**
* Clone is overridden to reduce heap churn.
*/
final public Constant clone() {
return this;
}
public String toString() {
@SuppressWarnings("unchecked")
final IVariable var = (IVariable) getProperty(Annotations.VAR);
if(var != null) {
// A constant which is really an as-bound variable.
return value.toString() + "[var=" + var + "]";
}
return value.toString();
}
final public boolean equals(final IVariableOrConstant o) {
if (o.isConstant() && value.equals(o.get())) {
return true;
}
return false;
}
final public boolean equals(final Object o) {
if (this == o)
return true;
if(!(o instanceof IConstant)) {
/*
* Incomparable types.
*
* Note: This used to permit IVariableOrConstant, but it is not
* possible to invoke get() on an IVariable without a bindingSet
* against which to resolve its asBound value.
*
* See https://sourceforge.net/apps/trac/bigdata/ticket/276
*/
return false;
}
final Object otherValue = ((IConstant) o).get();
// handles reference equality, including when both are null.
if (value == otherValue)
return true;
// handles value null when other is non-null.
if (value == null)
return false;
// compares non-null value with the other value.
if(value.equals(otherValue))
return true;
return false;
}
final public int hashCode() {
// return (int) (id ^ (id >>> 32));
return value.hashCode();
}
final public E get() {
return value;
}
final public E get(final IBindingSet bindingSet) {
return value;
}
final public String getName() {
throw new UnsupportedOperationException();
}
@SuppressWarnings("unchecked")
final public IVariable getVar() {
return (IVariable) getProperty(Annotations.VAR);
}
}