com.sun.tools.xjc.reader.gbind.Sequence Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2021 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;
/**
* {@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();
}
@Override
ElementSet lastSet() {
if(lastSet==null) {
if(rhs.isNullable())
lastSet = ElementSets.union(lhs.lastSet(),rhs.lastSet());
else
lastSet = rhs.lastSet();
}
return lastSet;
}
@Override
boolean isNullable() {
return isNullable;
}
@Override
void buildDAG(ElementSet incoming) {
lhs.buildDAG(incoming);
if(lhs.isNullable())
rhs.buildDAG(ElementSets.union(incoming,lhs.lastSet()));
else
rhs.buildDAG(lhs.lastSet());
}
@Override
public String toString() {
return '('+lhs.toString()+','+rhs.toString()+')';
}
}