modules/core/src/main/java/org/apache/ignite/internal/util/IgniteCursor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.ignite.internal.util;

import java.util.Iterator;
import org.apache.ignite.lang.IgniteInternalCheckedException;

/**
 * Simple cursor abstraction. Initial state must be "before first".
 */
public interface IgniteCursor<T> {
    /**
     * Attempt to move cursor position forward.
     *
     * @return {@code true} If we were able to move position of cursor forward.
     * @throws IgniteInternalCheckedException If failed.
     */
    boolean next() throws IgniteInternalCheckedException;

    /**
     * Gets element at current position. Must be called only after successful {@link #next()} call.
     *
     * @return Element at current position.
     * @throws IgniteInternalCheckedException If failed.
     */
    T get() throws IgniteInternalCheckedException;

    /**
     * Returns a wrapped {@link IgniteCursor cursor} over an {@link Iterator iterator}.
     *
     * @param iterator Iterator.
     */
    static <T> IgniteCursor<T> wrap(Iterator<T> iterator) {
        return new IgniteCursor<>() {
            T next;

            /** {@inheritDoc} */
            @Override
            public boolean next() {
                next = iterator.hasNext() ? iterator.next() : null;

                return next != null;
            }

            /** {@inheritDoc} */
            @Override
            public T get() {
                return next;
            }
        };
    }
}