ElementKindVisitor9.java

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package javax.lang.model.util;

import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.ModuleElement;

import static javax.lang.model.SourceVersion.RELEASE_11;

/**
 * A visitor of program elements based on their {@linkplain
 * ElementKind kind} with default behavior appropriate for source
 * versions {@link SourceVersion#RELEASE_9 RELEASE_9} through {@link
 * SourceVersion#RELEASE_11 RELEASE_11}.
 *
 * For {@linkplain
 * Element elements} <code><i>Xyz</i></code> that may have more than one
 * kind, the <code>visit<i>Xyz</i></code> methods in this class delegate
 * to the <code>visit<i>Xyz</i>As<i>Kind</i></code> method corresponding to the
 * first argument's kind.  The <code>visit<i>Xyz</i>As<i>Kind</i></code> methods
 * call {@link #defaultAction defaultAction}, passing their arguments
 * to {@code defaultAction}'s corresponding parameters.
 *
 * <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 or the
 * {@code ElementKind} {@code enum} used in this case may have
 * constants added to it in the future to accommodate new, currently
 * unknown, language structures added to future versions of the
 * Java&trade; 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 abstract element kind
 * 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.
 *
 * @spec JPMS
 * @see ElementKindVisitor6
 * @see ElementKindVisitor7
 * @see ElementKindVisitor8
 * @since 9
 */
// 元素访问器的细化版本（JDK9）
@SupportedSourceVersion(RELEASE_11)
public class ElementKindVisitor9<R, P> extends ElementKindVisitor8<R, P> {
    /**
     * Constructor for concrete subclasses; uses {@code null} for the
     * default value.
     */
    protected ElementKindVisitor9() {
        super(null);
    }
    
    /**
     * Constructor for concrete subclasses; uses the argument for the
     * default value.
     *
     * @param defaultValue the value to assign to {@link #DEFAULT_VALUE}
     */
    protected ElementKindVisitor9(R defaultValue) {
        super(defaultValue);
    }
    
    /**
     * {@inheritDoc}
     *
     * @param e the element to visit
     * @param p a visitor-specified parameter
     *
     * @return the result of {@code defaultAction}
     *
     * @implSpec This implementation calls {@code defaultAction}.
     */
    // 访问模块元素
    @Override
    public R visitModule(ModuleElement e, P p) {
        return defaultAction(e, p);
    }
}