org.javimmutable.collections.cursors.StandardCursor 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) 2017, 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.cursors;
import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Cursorable;
import org.javimmutable.collections.Func0;
import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.SplitCursor;
import org.javimmutable.collections.Tuple2;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
/**
* Utility class that implements standard Cursor behavior for classes that do not
* naturally start at a position before the first element. Such classes can pass
* a Source implementation to the of() method and this class will ensure that traversal
* does not start until the next() method is called and does not progress beyond the
* point where atEnd() is true.
*/
@Immutable
public abstract class StandardCursor
{
@SuppressWarnings("unchecked")
private static final Cursor EMPTY = new Start(new EmptySource());
/**
* Simple interface for classes that can iterate immediately (i.e. do not require a lazy start).
* A Source must start already pointing at a current value.
* Implementations of this interface must be immutable.
*/
public interface Source
{
/**
* @return true iff a call to advance() will fail
*/
boolean atEnd();
/**
* @return current value
*/
T currentValue();
/**
* @return new Source pointing at the next value or throw if no next value available
*/
Source advance();
default boolean isSplitAllowed()
{
return false;
}
default Tuple2, Source> splitSource()
{
throw new UnsupportedOperationException();
}
}
/**
* Creates an empty cursor that has no values.
*/
@SuppressWarnings("unchecked")
public static Cursor of()
{
return (Cursor)EMPTY;
}
/**
* Creates a Cursor for a Source created on demand using the supplied factory method.
* The Source will only be created when start() is called. This can be used to defer
* creation of a stateful Source object until necessary.
*/
public static Cursor of(Func0> sourceFactory)
{
return new FactoryStart<>(sourceFactory);
}
/**
* Creates a Cursor for the given Source. The Source must point to the first value to be iterated over
* or be empty.
*/
public static Cursor of(Source source)
{
return source.atEnd() ? of() : new Start<>(source);
}
/**
* Creates a Cursor for the given Indexed.
*/
public static Cursor of(Indexed source)
{
return new Start<>(new IndexedSource<>(source, 0, source.size()));
}
/**
* Creates a java.util.Iterator that iterates over values in the specified Source.
* The Source must point to the first value (i.e. cannot be
* be used for empty collections) to be iterated over.
*/
public static Iterator iterator(Source source)
{
return new SourceIterator<>(source);
}
/**
* Creates a Cursor over a range of integers. Useful for test purposes.
*/
public static Cursor forRange(int low,
int high)
{
return of(new RangeSource(low, high));
}
/**
* Creates a Cursor over a range of integers. Useful for test purposes.
*/
public static Cursor repeating(int count,
T value)
{
return of(new RepeatingValueCursorSource(count, value));
}
/**
* Utility method, useful in unit tests, that collects all of the values in the Cursor into a List
* and returns the List.
*/
public static List makeList(Cursor cursor)
{
List answer = new ArrayList<>();
for (cursor = cursor.start(); cursor.hasValue(); cursor = cursor.next()) {
answer.add(cursor.getValue());
}
return answer;
}
/**
* Utility method, useful in unit tests, that collects all of the values in the Iterator into a List
* and returns the List.
*/
public static List makeList(Iterator iterator)
{
List answer = new ArrayList<>();
while (iterator.hasNext()) {
answer.add(iterator.next());
}
return answer;
}
/**
* Creates a Cursorable that always returns an empty Cursor.
*/
public static Cursorable emptyCursorable()
{
return new Cursorable()
{
@Nonnull
@Override
public Cursor cursor()
{
return StandardCursor.of();
}
};
}
public static Source emptySource()
{
return new EmptySource<>();
}
@Immutable
private static class Start
extends AbstractStartCursor
{
private final Source source;
private Start(Source source)
{
this.source = source;
}
@Nonnull
@Override
public Cursor next()
{
return new Started<>(source);
}
}
@Immutable
private static class FactoryStart
extends AbstractStartCursor
{
private final Func0> factory;
private FactoryStart(Func0> factory)
{
this.factory = factory;
}
@Nonnull
@Override
public Cursor next()
{
return new Started<>(factory.apply());
}
}
@Immutable
private static class Started
extends AbstractStartedCursor
{
private final Source source;
private Started(Source source)
{
this.source = source;
}
@Nonnull
@Override
public Cursor next()
{
return source.atEnd() ? super.next() : new Started<>(source.advance());
}
@Override
public boolean hasValue()
{
return !source.atEnd();
}
@Override
public T getValue()
{
if (source.atEnd()) {
throw new NoValueException();
}
return source.currentValue();
}
@Override
public boolean isSplitAllowed()
{
return source.isSplitAllowed();
}
@Override
public SplitCursor splitCursor()
{
Tuple2, Source> split = source.splitSource();
return new SplitCursor<>(of(split.getFirst()), of(split.getSecond()));
}
}
@Immutable
private static class EmptySource
implements Source
{
@Override
public boolean atEnd()
{
return true;
}
@Override
public T currentValue()
{
throw new Cursor.NoValueException();
}
@Override
public Source advance()
{
throw new IllegalStateException();
}
}
@Immutable
static class RangeSource
implements Source
{
private final int low;
private final int high;
RangeSource(int low,
int high)
{
this.low = low;
this.high = high;
}
@Override
public boolean atEnd()
{
return low > high;
}
@Override
public Integer currentValue()
{
return low;
}
@Override
public Source advance()
{
return new RangeSource(low + 1, high);
}
@Override
public boolean isSplitAllowed()
{
return high > low;
}
@Override
public Tuple2, Source> splitSource()
{
if (low >= high) {
throw new UnsupportedOperationException();
}
final int middle = low + 1 + (high - low) / 2;
return Tuple2.of(new RangeSource(low, middle - 1), new RangeSource(middle, high));
}
}
@Immutable
private static class RepeatingValueCursorSource
implements StandardCursor.Source
{
private int count;
private final T value;
private RepeatingValueCursorSource(int count,
T value)
{
this.count = count;
this.value = value;
}
@Override
public boolean atEnd()
{
return count <= 0;
}
@Override
public T currentValue()
{
return value;
}
@Override
public StandardCursor.Source advance()
{
return new RepeatingValueCursorSource<>(count - 1, value);
}
@Override
public boolean isSplitAllowed()
{
return count >= 2;
}
@Override
public Tuple2, Source> splitSource()
{
if (count < 2) {
throw new UnsupportedOperationException();
}
final int left = count / 2;
final int right = count - left;
return Tuple2.of(new RepeatingValueCursorSource<>(left, value), new RepeatingValueCursorSource<>(right, value));
}
}
private static class SourceIterator
implements Iterator
{
private Source source;
private SourceIterator(Source source)
{
this.source = source;
}
@Override
public boolean hasNext()
{
return !source.atEnd();
}
@Override
public T next()
{
if (source.atEnd()) {
throw new NoSuchElementException();
}
final T value = source.currentValue();
source = source.advance();
return value;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
}
@Immutable
private static class IndexedSource
implements Source
{
private final Indexed list;
private final int index;
private final int limit;
private IndexedSource(Indexed list,
int index,
int limit)
{
this.list = list;
this.index = index;
this.limit = limit;
}
@Override
public boolean atEnd()
{
return index >= limit;
}
@Override
public T currentValue()
{
return list.get(index);
}
@Override
public Source advance()
{
return new IndexedSource<>(list, index + 1, limit);
}
@Override
public boolean isSplitAllowed()
{
return (limit - index) > 1;
}
@Override
public Tuple2, Source> splitSource()
{
final int splitIndex = index + (limit - index) / 2;
if (splitIndex == index) {
throw new UnsupportedOperationException();
}
return Tuple2.of(new IndexedSource<>(list, index, splitIndex), new IndexedSource<>(list, splitIndex, limit));
}
}
}