com.sun.tools.xjc.reader.gbind.Expression Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2022 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package com.sun.tools.xjc.reader.gbind;
/**
* This builds content models.
*
* @author Kohsuke Kawaguchi
*/
public abstract class Expression {
/**
* Default constructor.
*/
protected Expression() {}
/**
* Computes {@code LAST(exp)}
*/
abstract ElementSet lastSet();
/**
* True of {@code \epsilon \in L(exp)}
*/
abstract boolean isNullable();
/**
* Builds up a DAG among {@link Element}s in this expression.
*/
abstract void buildDAG(ElementSet incoming);
/**
* {@link Expression} that represents epsilon, the length-0 string.
*/
public static final Expression EPSILON = new Expression() {
@Override
ElementSet lastSet() {
return ElementSet.EMPTY_SET;
}
@Override
boolean isNullable() {
return true;
}
@Override
void buildDAG(ElementSet incoming) {
// noop
}
@Override
public String toString() {
return "-";
}
};
}