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

import java.util.Set;

This builds content models.
Author:
Kohsuke Kawaguchi/**
 * This builds content models.
 *
 * @author Kohsuke Kawaguchi
 */
public abstract class Expression {

    
Computes LAST(exp) /**
     * Computes {@code LAST(exp)}
     */
    abstract ElementSet lastSet();

    
True of \epsilon \in L(exp) /**
     * True of {@code \epsilon \in L(exp)}
     */
    abstract boolean isNullable();

    
Builds up a DAG among Elements in this expression. /**
     * Builds up a DAG among {@link Element}s in this expression.
     */
    abstract void buildDAG(ElementSet incoming);

    
Expression that represents epsilon, the length-0 string. /**
     * {@link Expression} that represents epsilon, the length-0 string.
     */
    public static final Expression EPSILON = new Expression() {
        ElementSet lastSet() {
            return ElementSet.EMPTY_SET;
        }

        boolean isNullable() {
            return true;
        }

        void buildDAG(ElementSet incoming) {
            // noop
        }

        public String toString() {
            return "-";
        }
    };
}