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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.collections;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* @author Simon Thoresen Hult
*/
public abstract class LazySet<E> implements Set<E> {
private Set<E> delegate = newEmpty();
@Override
public final int size() {
return delegate.size();
}
@Override
public final boolean isEmpty() {
return delegate.isEmpty();
}
@Override
public final boolean contains(Object o) {
return delegate.contains(o);
}
@Override
public final Iterator<E> iterator() {
return delegate.iterator();
}
@Override
public final Object[] toArray() {
return delegate.toArray();
}
@Override
public final <T> T[] toArray(T[] a) {
// noinspection SuspiciousToArrayCall
return delegate.toArray(a);
}
@Override
public final boolean add(E e) {
return delegate.add(e);
}
@Override
public final boolean remove(Object o) {
return delegate.remove(o);
}
@Override
public final boolean containsAll(Collection<?> c) {
return delegate.containsAll(c);
}
@Override
public final boolean addAll(Collection<? extends E> c) {
return delegate.addAll(c);
}
@Override
public final boolean retainAll(Collection<?> c) {
return delegate.retainAll(c);
}
@Override
public final boolean removeAll(Collection<?> c) {
return delegate.removeAll(c);
}
@Override
public final void clear() {
delegate.clear();
}
@Override
public final int hashCode() {
return delegate.hashCode();
}
@Override
public final boolean equals(Object obj) {
return obj == this || (obj instanceof Set && delegate.equals(obj));
}
private Set<E> newEmpty() {
return new EmptySet();
}
private Set<E> newSingleton(E e) {
return new SingletonSet(e);
}
protected abstract Set<E> newDelegate();
final Set<E> getDelegate() {
return delegate;
}
class EmptySet extends AbstractSet<E> {
@Override
public Iterator<E> iterator() {
return Collections.emptyIterator();
}
@Override
public int size() {
return 0;
}
@Override
public boolean add(E e) {
delegate = newSingleton(e);
return true;
}
@Override
public boolean addAll(Collection<? extends E> c) {
switch (c.size()) {
case 0:
return false;
case 1:
add(c.iterator().next());
return true;
default:
delegate = newDelegate();
delegate.addAll(c);
return true;
}
}
}
class SingletonSet extends AbstractSet<E> {
final E element;
SingletonSet(E e) {
this.element = e;
}
@Override
public Iterator<E> iterator() {
return new Iterator<E>() {
boolean hasNext = true;
@Override
public boolean hasNext() {
return hasNext;
}
@Override
public E next() {
if (hasNext) {
hasNext = false;
return element;
} else {
throw new NoSuchElementException();
}
}
@Override
public void remove() {
if (hasNext) {
throw new IllegalStateException();
} else {
delegate = newEmpty();
}
}
};
}
@Override
public int size() {
return 1;
}
@Override
public boolean add(E e) {
if (contains(e)) {
return false;
} else {
delegate = newDelegate();
delegate.add(element);
delegate.add(e);
return true;
}
}
@Override
public boolean addAll(Collection<? extends E> c) {
switch (c.size()) {
case 0:
return false;
case 1:
return add(c.iterator().next());
default:
delegate = newDelegate();
delegate.add(element);
delegate.addAll(c);
return true;
}
}
}
public static <E> LazySet<E> newHashSet() {
return new LazySet<E>() {
@Override
protected Set<E> newDelegate() {
return new HashSet<>();
}
};
}
}
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