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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* ASM: a very small and fast Java bytecode manipulation framework
* Copyright (c) 2000-2011 INRIA, France Telecom
* All rights reserved.
*
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* modification, are permitted provided that the following conditions
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* notice, this list of conditions and the following disclaimer in the
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* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
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package jdk.internal.org.objectweb.asm.tree.analysis;
import java.util.AbstractSet;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
An immutable set of at most two elements, optimized for speed compared to a generic set
implementation.
Author: Eric Bruneton
/**
* An immutable set of at most two elements, optimized for speed compared to a generic set
* implementation.
*
* @author Eric Bruneton
*/
final class SmallSet<T> extends AbstractSet<T> {
The first element of this set, maybe null. /** The first element of this set, maybe {@literal null}. */
private final T element1;
The second element of this set, maybe null. If SmallSet<T>.element1 is null then this field must be null, otherwise it must be different from SmallSet<T>.element1. /**
* The second element of this set, maybe {@literal null}. If {@link #element1} is {@literal null}
* then this field must be {@literal null}, otherwise it must be different from {@link #element1}.
*/
private final T element2;
// -----------------------------------------------------------------------------------------------
// Constructors
// -----------------------------------------------------------------------------------------------
Constructs an empty set. /** Constructs an empty set. */
SmallSet() {
this.element1 = null;
this.element2 = null;
}
Constructs a set with exactly one element.
Params: - element – the unique set element.
/**
* Constructs a set with exactly one element.
*
* @param element the unique set element.
*/
SmallSet(final T element) {
this.element1 = element;
this.element2 = null;
}
Constructs a new SmallSet. Params: - element1 – see
SmallSet<T>.element1. - element2 – see
SmallSet<T>.element2.
/**
* Constructs a new {@link SmallSet}.
*
* @param element1 see {@link #element1}.
* @param element2 see {@link #element2}.
*/
private SmallSet(final T element1, final T element2) {
this.element1 = element1;
this.element2 = element2;
}
// -----------------------------------------------------------------------------------------------
// Implementation of the inherited abstract methods
// -----------------------------------------------------------------------------------------------
@Override
public Iterator<T> iterator() {
return new IteratorImpl<>(element1, element2);
}
@Override
public int size() {
if (element1 == null) {
return 0;
} else if (element2 == null) {
return 1;
} else {
return 2;
}
}
// -----------------------------------------------------------------------------------------------
// Utility methods
// -----------------------------------------------------------------------------------------------
Returns the union of this set and of the given set.
Params: - otherSet – another small set.
Returns: the union of this set and of otherSet.
/**
* Returns the union of this set and of the given set.
*
* @param otherSet another small set.
* @return the union of this set and of otherSet.
*/
Set<T> union(final SmallSet<T> otherSet) {
// If the two sets are equal, return this set.
if ((otherSet.element1 == element1 && otherSet.element2 == element2)
|| (otherSet.element1 == element2 && otherSet.element2 == element1)) {
return this;
}
// If one set is empty, return the other.
if (otherSet.element1 == null) {
return this;
}
if (element1 == null) {
return otherSet;
}
// At this point we know that the two sets are non empty and are different.
// If otherSet contains exactly one element:
if (otherSet.element2 == null) {
// If this set also contains exactly one element, we have two distinct elements.
if (element2 == null) {
return new SmallSet<>(element1, otherSet.element1);
}
// If otherSet is included in this set, return this set.
if (otherSet.element1 == element1 || otherSet.element1 == element2) {
return this;
}
}
// If this set contains exactly one element, then otherSet contains two elements (because of the
// above tests). Thus, if otherSet contains this set, return otherSet:
if (element2 == null && (element1 == otherSet.element1 || element1 == otherSet.element2)) {
return otherSet;
}
// At this point we know that there are at least 3 distinct elements, so we need a generic set
// to store the result.
HashSet<T> result = new HashSet<>(4);
result.add(element1);
if (element2 != null) {
result.add(element2);
}
result.add(otherSet.element1);
if (otherSet.element2 != null) {
result.add(otherSet.element2);
}
return result;
}
static class IteratorImpl<T> implements Iterator<T> {
The next element to return in next. Maybe null. /** The next element to return in {@link #next}. Maybe {@literal null}. */
private T firstElement;
The element to return in next, after IteratorImpl<T>.firstElement is returned. If IteratorImpl<T>.firstElement is null then this field must be null, otherwise it must be different from IteratorImpl<T>.firstElement. /**
* The element to return in {@link #next}, after {@link #firstElement} is returned. If {@link
* #firstElement} is {@literal null} then this field must be {@literal null}, otherwise it must
* be different from {@link #firstElement}.
*/
private T secondElement;
IteratorImpl(final T firstElement, final T secondElement) {
this.firstElement = firstElement;
this.secondElement = secondElement;
}
@Override
public boolean hasNext() {
return firstElement != null;
}
@Override
public T next() {
if (firstElement == null) {
throw new NoSuchElementException();
}
T element = firstElement;
firstElement = secondElement;
secondElement = null;
return element;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
}