msv.msv.src.com.sun.msv.grammar.ReferenceExp Maven / Gradle / Ivy
/*
* @(#)$Id: ReferenceExp.java 1620 2003-12-12 21:36:38Z kohsuke $
*
* Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
*
* This software is the proprietary information of Sun Microsystems, Inc.
* Use is subject to license terms.
*
*/
package com.sun.msv.grammar;
/**
* Reference to the other expression.
*
*
* In RELAX grammar, this class is used as a base class of elementRule reference
* and hedgeRule reference.
* TREX uses this class directly.
*
*
* This object is created and controlled by TREXGrammar/RELAXModule object,
* rather than ExpressionPool. Therefore, this object is not a subject to unification.
*
*
* This class can be derived. In fact, many classes derive this class.
*
* @author Kohsuke KAWAGUCHI
*/
public class ReferenceExp extends Expression {
/** child expression. Due to the possible forward reference,
* this variable is not available when the object is instanciated.
*
* Actual expression will be set once if the definition is parsed.
*/
public Expression exp = null;
/** name of the referenced expression.
*
* can be null for anonymously referenced expression.
*/
public final String name;
public ReferenceExp( String name ) {
this.name = name;
}
public ReferenceExp( String name, Expression exp ) {
this(name);
this.exp = exp;
}
protected final int calcHashCode() {
return System.identityHashCode(this);
}
/**
* checks if this ReferenceExp is properly defined.
* this method is used to detect undeclared definitions.
* Derived classes can override this method.
*/
public boolean isDefined() {
return exp!=null;
}
public boolean equals( Object o ) {
return this==o;
}
protected boolean calcEpsilonReducibility() {
if(exp==null)
// // actual expression is not supplied yet.
// // actual definition of the referenced expression must be supplied
// // before any computation over the grammar.
// throw new Error(); // assertion failed.
return false;
// this method can be called while parsing a grammar.
// in that case, epsilon reducibility is just used for approximation.
// therefore we can safely return false.
return exp.isEpsilonReducible();
}
// derived class must be able to behave as a ReferenceExp
public final Object visit( ExpressionVisitor visitor ) { return visitor.onRef(this); }
public final Expression visit( ExpressionVisitorExpression visitor ){ return visitor.onRef(this); }
public final boolean visit( ExpressionVisitorBoolean visitor ) { return visitor.onRef(this); }
public final void visit( ExpressionVisitorVoid visitor ) { visitor.onRef(this); }
// serialization support
private static final long serialVersionUID = 1;
}