org.javimmutable.collections.Cursor 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

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.

There is a newer version: 3.2.1

Show newest version

///###////////////////////////////////////////////////////////////////////////
//
// 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;

import javax.annotation.Nonnull;

/**
 * Implemented by objects used to traverse persistent data structures.
 * The iterators themselves must be immutable and always create a new
 * iterator when start() or next() is called.
 */
public interface Cursor
    extends Iterable
{
    /**
     * Thrown by hasValue() and getValue() if the cursor has not been started by calling next() yet.
     */
    class NotStartedException
        extends IllegalStateException
    {
    }

    /**
     * Thrown by getValue() if the Cursor's hasValue() method returns false.
     */
    class NoValueException
        extends IllegalStateException
    {
    }

    /**
     * All Cursors are created in a pre-start position pointing "before" the first element.  Once traversal has begun a
     * Cursor points to some element in the collection or to end ("after" the last element).  The start() method
     * advances to the first element if traversal has not yet started or does nothing if traversal has
     * already started.  Either next() or start() can be used to initiate a traversal however start() is
     * safer since it can be used safely on already started cursors as well as not-started ones.  This distinction
     * is useful when passing a Cursor as parameter to a method that will traverse from the Cursor's current position
     * forward and using start() prevents it from skipping the current value.
     * 
     * Must always return a non-null Cursor.
     *
     * @return Cursor for first position or this if already started
     */
    @Nonnull
    Cursor start();

    /**
     * Advances to the next (possibly first) value.  Must always return a non-null Cursor.
     * A newly created Cursor must always point to "before" the first value because next() (or start()) must
     * always be called once before retrieving the first value.  If the Cursor is already at the end
     * of its sequence then it should return a Cursor that will always return false for hasValue().
     *
     * @return Cursor for next position
     */
    @Nonnull
    Cursor next();

    /**
     * Read-only method with no side effects that determines if the Cursor currently has a value.
     * Users of the Cursor will always call this after calling next() to see if they have reached
     * the end of the sequence.  If hasValue() returns true then next() will be called.  If hasValue()
     * returns false then next() must not be called.
     *
     * @return true iff getValue() can be called
     */
    boolean hasValue();

    /**
     * Return the value at the Cursor's position.  Only valid if a call to hasValue() would return true.
     *
     * @return current value
     * @throws IllegalStateException if getValue() is not allowed for this iterator
     */
    T getValue();

    default boolean isSplitAllowed()
    {
        return false;
    }

    default SplitCursor splitCursor()
    {
        throw new UnsupportedOperationException();
    }
}