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package javax.lang.model.util;

import javax.lang.model.type.*;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import static javax.lang.model.SourceVersion.*;

/**
 * A simple visitor of types with default behavior appropriate for the
 * {@link SourceVersion#RELEASE_7 RELEASE_7} source version.
 *
 * Visit methods corresponding to {@code RELEASE_7} and earlier
 * language constructs 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 TypeVisitor} 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&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 simple type 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.
 *
 * <p>Note that adding a default implementation of a new visit method
 * in a visitor class will occur instead of adding a <em>default
 * method</em> directly in the visitor interface since a Java SE 8
 * language feature cannot be used to this version of the API since
 * this version is required to be runnable on Java SE 7
 * implementations.  Future versions of the API that are only required
 * to run on Java SE 8 and later may take advantage of default methods
 * in this situation.
 *
 * @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.
 *
 * @see SimpleTypeVisitor6
 * @see SimpleTypeVisitor8
 * @since 1.7
 */
@SupportedSourceVersion(RELEASE_7)
public class SimpleTypeVisitor7<R, P> extends SimpleTypeVisitor6<R, P> {
    /**
     * Constructor for concrete subclasses; uses {@code null} for the
     * default value.
     */
    protected SimpleTypeVisitor7(){
        super(null);
    }

    /**
     * Constructor for concrete subclasses; uses the argument for the
     * default value.
     *
     * @param defaultValue the value to assign to {@link #DEFAULT_VALUE}
     */
    protected SimpleTypeVisitor7(R defaultValue){
        super(defaultValue);
    }

    /**
     * This implementation visits a {@code UnionType} by calling
     * {@code defaultAction}.
     *
     * @param t  {@inheritDoc}
     * @param p  {@inheritDoc}
     * @return the result of {@code defaultAction}
     */
    @Override
    public R visitUnion(UnionType t, P p) {
        return defaultAction(t, p);
    }
}
