/*
* @(#)ElementScanner6.java 1.7 06/08/15
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package javax.lang.model.util;
import javax.lang.model.element.*;
import javax.annotation.processing.SupportedSourceVersion;
import static javax.lang.model.element.ElementKind.*;
import javax.lang.model.SourceVersion;
import static javax.lang.model.SourceVersion.*;
/**
* A scanning visitor of program elements with default behavior
* appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
* source version. The <tt>visit<i>XYZ</i></tt> methods in this
* class scan their component elements by calling {@code scan} on
* their {@linkplain Element#getEnclosedElements enclosed elements},
* {@linkplain ExecutableElement#getParameters parameters}, etc., as
* indicated in the individual method specifications. A subclass can
* control the order elements are visited by overriding the
* <tt>visit<i>XYZ</i></tt> methods. Note that clients of a scanner
* may get the desired behavior be invoking {@code v.scan(e, p)} rather
* than {@code v.visit(e, p)} on the root objects of interest.
*
* <p>When a subclass overrides a <tt>visit<i>XYZ</i></tt> method, the
* new method can cause the enclosed elements to be scanned in the
* default way by calling <tt>super.visit<i>XYZ</i></tt>. In this
* fashion, the concrete visitor can control the ordering of traversal
* over the component elements with respect to the additional
* processing; for example, consistently calling
* <tt>super.visit<i>XYZ</i></tt> at the start of the overridden
* methods will yield a preorder traversal, etc. If the component
* elements should be traversed in some other order, instead of
* calling <tt>super.visit<i>XYZ</i></tt>, an overriding visit method
* should call {@code scan} with the elements in the desired order.
*
* <p> Methods in this class may be overridden subject to their
* general contract. Note that annotating methods in concrete
* subclasses with {@link java.lang.Override @Override} will help
* ensure that methods are overridden as intended.
*
* <p> <b>WARNING:</b> The {@code ElementVisitor} interface
* implemented by this class may have methods added to it in the
* future to accommodate new, currently unknown, language structures
* added to future versions of the Java™ programming language.
* Therefore, methods whose names begin with {@code "visit"} may be
* added to this class in the future; to avoid incompatibilities,
* classes which extend this class should not declare any instance
* methods with names beginning with {@code "visit"}.
*
* <p>When such a new visit method is added, the default
* implementation in this class will be to call the {@link
* #visitUnknown visitUnknown} method. A new element scanner visitor
* class will also be introduced to correspond to the new language
* level; this visitor will have different default behavior for the
* visit method in question. When the new visitor is introduced, all
* or portions of this visitor may be deprecated.
*
* @param <R> the return type of this visitor's methods. Use {@link
* Void} for visitors that do not need to return results.
* @param <P> the type of the additional parameter to this visitor's
* methods. Use {@code Void} for visitors that do not need an
* additional parameter.
*
* @author Joseph D. Darcy
* @author Scott Seligman
* @author Peter von der Ahé
* @version 1.7 06/08/15
* @since 1.6
*/
@SupportedSourceVersion(RELEASE_6)
public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> {
/**
* The specified default value.
*/
protected final R DEFAULT_VALUE;
/**
* Constructor for concrete subclasses; uses {@code null} for the
* default value.
*/
protected ElementScanner6(){
DEFAULT_VALUE = null;
}
/**
* Constructor for concrete subclasses; uses the argument for the
* default value.
*/
protected ElementScanner6(R defaultValue){
DEFAULT_VALUE = defaultValue;
}
/**
* Iterates over the given elements and calls {@link
* #scan(Element, Object) scan(Element, P)} on each one. Returns
* the result of the last call to {@code scan} or {@code
* DEFAULT_VALUE} for an empty iterable.
*
* @param iterable the elements to scan
* @param p additional parameter
* @return the scan of the last element or {@code DEFAULT_VALUE} if no elements
*/
public final R scan(Iterable<? extends Element> iterable, P p) {
R result = DEFAULT_VALUE;
for(Element e : iterable)
result = scan(e, p);
return result;
}
/**
* Processes an element by calling {@code e.accept(this, p)};
* this method may be overridden by subclasses.
* @return the result of visiting {@code e}.
*/
public R scan(Element e, P p) {
return e.accept(this, p);
}
/**
* Convenience method equivalent to {@code v.scan(e, null)}.
* @return the result of scanning {@code e}.
*/
public final R scan(Element e) {
return scan(e, null);
}
/**
* {@inheritDoc} This implementation scans the enclosed elements.
*
* @param e the element to visit
* @param p a visitor-specified parameter
* @return the result of scanning
*/
public R visitPackage(PackageElement e, P p) {
return scan(e.getEnclosedElements(), p);
}
/**
* {@inheritDoc} This implementation scans the enclosed elements.
*
* @param e the element to visit
* @param p a visitor-specified parameter
* @return the result of scanning
*/
public R visitType(TypeElement e, P p) {
return scan(e.getEnclosedElements(), p);
}
/**
* {@inheritDoc} This implementation scans the enclosed elements.
*
* @param e the element to visit
* @param p a visitor-specified parameter
* @return the result of scanning
*/
public R visitVariable(VariableElement e, P p) {
return scan(e.getEnclosedElements(), p);
}
/**
* {@inheritDoc} This implementation scans the parameters.
*
* @param e the element to visit
* @param p a visitor-specified parameter
* @return the result of scanning
*/
public R visitExecutable(ExecutableElement e, P p) {
return scan(e.getParameters(), p);
}
/**
* {@inheritDoc} This implementation scans the enclosed elements.
*
* @param e the element to visit
* @param p a visitor-specified parameter
* @return the result of scanning
*/
public R visitTypeParameter(TypeParameterElement e, P p) {
return scan(e.getEnclosedElements(), p);
}
}
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