src/java.compiler/share/classes/javax/lang/model/element/UnknownElementException.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package javax.lang.model.element;

import java.io.Serial;

import javax.lang.model.UnknownEntityException;

/**
 * Indicates that an unknown kind of element was encountered.  This
 * can occur if the language evolves and new kinds of elements are
 * added to the {@code Element} hierarchy.  May be thrown by an
 * {@linkplain ElementVisitor element visitor} to indicate that the
 * visitor was created for a prior version of the language.
 *
 * @see ElementVisitor#visitUnknown
 * @since 1.6
 */
public class UnknownElementException extends UnknownEntityException {

    @Serial
    private static final long serialVersionUID = 269L;

    private transient Element element;
    private transient Object parameter;

    /**
     * Creates a new {@code UnknownElementException}.  The {@code p}
     * parameter may be used to pass in an additional argument with
     * information about the context in which the unknown element was
     * encountered; for example, the visit methods of {@link
     * ElementVisitor} may pass in their additional parameter.
     *
     * @param e the unknown element, may be {@code null}
     * @param p an additional parameter, may be {@code null}
     */
    public UnknownElementException(Element e, Object p) {
        super("Unknown element: \"" + e + "\"");
        element = e;
        this.parameter = p;
    }

    /**
     * Returns the unknown element.
     * The value may be unavailable if this exception has been
     * serialized and then read back in.
     *
     * @return the unknown element, or {@code null} if unavailable
     */
    public Element getUnknownElement() {
        return element;
    }

    /**
     * Returns the additional argument.
     *
     * @return the additional argument, or {@code null} if unavailable
     */
    public Object getArgument() {
        return parameter;
    }
}