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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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package com.sun.tools.internal.xjc.reader.gbind;

/**

 * {@link Expression} that represents a concatanation of two expressions

 * "A,B".

 *

 * @author Kohsuke Kawaguchi

 */

public final class Sequence extends Expression {

    /**

     * 'A' of 'A,B'

     */

    private final Expression lhs;

    /**

     * 'B' of 'A,B'

     */

    private final Expression rhs;

    /**

     * Compute this value eagerly for better performance

     */

    private final boolean isNullable;

    /**

     * Cached value of {@link #lastSet()} for better performance.

     * Sequence tends to be where the recursive lastSet computation occurs.

     */

    private ElementSet lastSet;

    public Sequence(Expression lhs, Expression rhs) {

        this.lhs = lhs;

        this.rhs = rhs;

        isNullable = lhs.isNullable() && rhs.isNullable();

    }

    ElementSet lastSet() {

        if(lastSet==null) {

            if(rhs.isNullable())

                lastSet = ElementSets.union(lhs.lastSet(),rhs.lastSet());

            else

                lastSet = rhs.lastSet();

        }

        return lastSet;

    }

    boolean isNullable() {

        return isNullable;

    }

    void buildDAG(ElementSet incoming) {

        lhs.buildDAG(incoming);

        if(lhs.isNullable())

            rhs.buildDAG(ElementSets.union(incoming,lhs.lastSet()));

        else

            rhs.buildDAG(lhs.lastSet());

    }

    public String toString() {

        return '('+lhs.toString()+','+rhs.toString()+')';

    }

}