com.adobe.granite.ui.components.PagingIterator Maven / Gradle / Ivy

Go to download
/*************************************************************************
 *
 * ADOBE CONFIDENTIAL
 * __________________
 *
 *  Copyright 2014 Adobe Systems Incorporated
 *  All Rights Reserved.
 *
 * NOTICE:  All information contained herein is, and remains
 * the property of Adobe Systems Incorporated and its suppliers,
 * if any.  The intellectual and technical concepts contained
 * herein are proprietary to Adobe Systems Incorporated and its
 * suppliers and are protected by trade secret or copyright law.
 * Dissemination of this information or reproduction of this material
 * is strictly forbidden unless prior written permission is obtained
 * from Adobe Systems Incorporated.
 **************************************************************************/
package com.adobe.granite.ui.components;

import java.util.Iterator;

import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;

/**
 * A wrapper iterator to supports paging.
 * 
 * If you have access to Collection 4.1, it is recommended to use
 * {@code IteratorUtils#boundedIterator(Iterator, long, long)} instead.
 */
public class PagingIterator implements Iterator {
    private Iterator it;

    private Integer offset;

    private Integer limit;

    private int limitCounter = 0;

    /**
     * Instantiates a new paging wrapper of the given iterator.
     * 
     * The iterator is iterated immediately as per {@code offset}.
     *
     * @param it
     *            The iterator to wrap
     * @param offset
     *            The offset of the paging; {@code null} to do paging without
     *            offset.
     * @param limit
     *            The limit of the paging; {@code null} to do paging without limit.
     * @throws IllegalArgumentException
     *             When either offset or limit is negative
     */
    public PagingIterator(@Nonnull Iterator it, @CheckForNull Integer offset, @CheckForNull Integer limit)
            throws IllegalArgumentException {
        this.it = it;
        this.offset = offset;
        this.limit = limit;

        if (offset != null && offset < 0) {
            throw new IllegalArgumentException("offset is negative");
        }

        if (limit != null && limit < 0) {
            throw new IllegalArgumentException("limit is negative");
        }

        doOffset();
    }

    private void doOffset() {
        if (offset == null) {
            return;
        }

        for (int i = 0; i < offset && it.hasNext(); i++) {
            it.next();
        }
    }

    @Override
    public boolean hasNext() {
        if (limit == null) {
            return it.hasNext();
        }

        return limitCounter < limit && it.hasNext();
    }

    @Override
    public E next() {
        E next = it.next();
        limitCounter++;
        return next;
    }

    @Override
    public void remove() {
        it.remove();
    }
}