org.javimmutable.collections.iterators.GenericIterator Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of javimmutable-collections Show documentation
Show all versions of javimmutable-collections Show documentation
Library providing immutable/persistent collection classes for
Java. While collections are immutable they provide methods for
adding and removing values by creating new modified copies of
themselves. Each copy shares almost all of its structure with
other copies to minimize memory consumption.
///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2019, Burton Computer Corporation
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
// distribution.
//
// Neither the name of the Burton Computer Corporation nor the names
// of its contributors may be used to endorse or promote products
// derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package org.javimmutable.collections.iterators;
import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.SplitIterator;
import org.javimmutable.collections.SplitableIterable;
import org.javimmutable.collections.SplitableIterator;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
import java.util.NoSuchElementException;
@ThreadSafe
public class GenericIterator
extends AbstractSplitableIterator
{
static final int MIN_SIZE_FOR_SPLIT = 32;
private final Iterable root;
private final int limit;
private int offset;
private boolean uninitialized;
private State state;
public GenericIterator(@Nonnull Iterable root,
int offset,
int limit)
{
assert offset <= limit;
this.root = root;
this.limit = limit;
this.offset = offset;
uninitialized = true;
}
public interface Iterable
extends SplitableIterable
{
@Nullable
State iterateOverRange(@Nullable State parent,
int offset,
int limit);
int iterableSize();
@Nonnull
default SplitableIterator iterator()
{
return new GenericIterator<>(this, 0, iterableSize());
}
}
public interface State
{
default boolean hasValue()
{
return false;
}
default T value()
{
throw new NoSuchElementException();
}
State advance();
}
@Override
public synchronized boolean hasNext()
{
return prepare();
}
@Override
public synchronized T next()
{
if (!prepare()) {
throw new NoSuchElementException();
}
final T answer = state.value();
offset += 1;
if (offset < limit) {
state = state.advance();
} else {
state = null;
}
assert offset <= limit;
return answer;
}
@Override
public synchronized boolean isSplitAllowed()
{
return (limit - offset) >= MIN_SIZE_FOR_SPLIT;
}
@Nonnull
@Override
public synchronized SplitIterator splitIterator()
{
final int splitIndex = offset + (limit - offset) / 2;
return new SplitIterator<>(new GenericIterator<>(root, offset, splitIndex),
new GenericIterator<>(root, splitIndex, limit));
}
private boolean prepare()
{
if (uninitialized) {
state = root.iterateOverRange(null, offset, limit);
uninitialized = false;
}
while (state != null) {
if (state.hasValue()) {
return true;
}
state = state.advance();
}
return false;
}
public static State valueState(State parent,
T value)
{
return new SingleValueState<>(parent, value);
}
public static Iterable valueIterable(T value)
{
return new Iterable()
{
@Override
public State iterateOverRange(@Nullable State parent,
int offset,
int limit)
{
assert offset >= 0 && offset <= limit && limit <= 1;
if (offset == limit) {
return parent;
} else {
return new SingleValueState(parent, value);
}
}
@Override
public int iterableSize()
{
return 1;
}
};
}
public static State multiValueState(@Nullable State parent,
@Nonnull Indexed values,
int offset,
int limit)
{
assert offset >= 0 && offset <= limit && limit <= values.size();
return new MultiValueState<>(parent, values, offset, limit);
}
public static State indexedState(State parent,
Indexed> children,
int offset,
int limit)
{
assert 0 <= offset && offset <= limit;
if (offset == limit) {
return parent;
} else {
return new IndexedState<>(parent, children, offset, limit);
}
}
private static class SingleValueState
implements State
{
private final State parent;
private final T value;
private boolean available;
private SingleValueState(State parent,
T value)
{
this.parent = parent;
this.value = value;
available = true;
}
@Override
public boolean hasValue()
{
return available;
}
@Override
public T value()
{
assert available;
available = false;
return value;
}
@Override
public State advance()
{
assert !available;
return parent;
}
}
private static class MultiValueState
implements GenericIterator.State
{
private final GenericIterator.State parent;
private final Indexed values;
private final int limit;
private int offset;
private MultiValueState(@Nullable GenericIterator.State parent,
@Nonnull Indexed values,
int offset,
int limit)
{
this.parent = parent;
this.values = values;
this.offset = offset;
this.limit = limit;
}
@Override
public boolean hasValue()
{
return offset < limit;
}
@Override
public T value()
{
return values.get(offset);
}
@Nullable
@Override
public GenericIterator.State advance()
{
offset += 1;
if (offset < limit) {
return this;
} else {
return parent;
}
}
}
private static class IndexedState
implements State
{
private final State parent;
private final Indexed> children;
private int offset;
private int limit;
private int index;
public IndexedState(State parent,
Indexed> children,
int offset,
int limit)
{
this.parent = parent;
this.children = children;
this.limit = limit;
this.offset = offset;
index = 0;
}
@Override
public State advance()
{
final Iterable child = children.get(index);
final int size = child.iterableSize();
if (offset >= size) {
index += 1;
offset -= size;
limit -= size;
return this;
} else if (limit <= size) {
return child.iterateOverRange(parent, offset, limit);
} else {
final State answer = child.iterateOverRange(this, offset, size);
index += 1;
offset = 0;
limit -= size;
return answer;
}
}
}
}