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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) 2014, Burton Computer Corporation
// All rights reserved.
//
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//
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//
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// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
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// Neither the name of the Burton Computer Corporation nor the names
// of its contributors may be used to endorse or promote products
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//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package org.javimmutable.collections.cursors;
import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.common.IteratorAdaptor;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* 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.
*/
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.
*
* @param
*/
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();
}
/**
* Creates an empty cursor that has no values.
*
* @param
* @return
*/
@SuppressWarnings("unchecked")
public static Cursor of()
{
return (Cursor)EMPTY;
}
/**
* Creates a Cursor for the given Source. The Source must point to the first value (i.e. cannot be
* be used for empty collections) to be iterated over.
*
* @param source
* @param
* @return
*/
public static Cursor of(Source source)
{
return new Start(source);
}
/**
* 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.
*
* @param source
* @param
* @return
*/
public static Iterator iterator(Source source)
{
return new SourceIterator(source);
}
/**
* Creates a Cursor over a range of integers. Useful for test purposes.
*
* @param low
* @param high
* @return
*/
public static Cursor forRange(int low,
int high)
{
return StandardCursor.of(new RangeSource(low, high));
}
/**
* Utility method, useful in unit tests, that collects all of the values in the Cursor into a List
* and returns the List.
*
* @param cursor
* @param
* @return
*/
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;
}
private static class Start
extends AbstractStartCursor
{
private final Source source;
private Start(Source source)
{
this.source = source;
}
@Override
public Cursor next()
{
return new Started(source);
}
@Override
public Iterator iterator()
{
return IteratorAdaptor.of(this);
}
}
private static class Started
extends AbstractStartedCursor
{
private final Source source;
private Started(Source source)
{
this.source = source;
}
@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 Iterator iterator()
{
return IteratorAdaptor.of(this);
}
}
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();
}
}
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);
}
}
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()
{
final T value = source.currentValue();
source = source.advance();
return value;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
}
}