modules/core/src/main/java/org/apache/ignite/internal/util/MutableSingletonList.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.AbstractList;

/**
 * List that can contain maximum of one element. Does not allow null element to be added.
 */
public class MutableSingletonList<E> extends AbstractList<E> {

    /** The only element of collection. */
    private E element;

    /** {@inheritDoc} */
    @Override public E get(int index) {
        if (index != 0 || element == null)
            throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size());

        return element;
    }

    /** {@inheritDoc} */
    @Override public void add(int index, E element) {
        if (element == null)
            throw new IllegalArgumentException("Cannot add null element to list");
        else if (index != 0)
            throw new IllegalStateException("Element already added to singleton list");
        else
            this.element = element;
    }

    /** {@inheritDoc} */
    @Override public int size() {
        return element == null ? 0 : 1;
    }
}