core/src/main/java/org/apache/calcite/util/UnmodifiableArrayList.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.calcite.util;

import java.util.AbstractList;
import java.util.Objects;
import java.util.RandomAccess;

/**
 * A view onto an array that cannot be modified by the client.
 *
 * <p>Since the array is not copied, modifications to the array will be
 * reflected in the list.
 *
 * <p>Null elements are allowed.
 *
 * <p>Quick and low-memory, like {@link java.util.Arrays#asList(Object[])}, but
 * unmodifiable.
 *
 * @param <E> Element type
 */
public class UnmodifiableArrayList<E>
    extends AbstractList<E>
    implements RandomAccess {
  private final E[] elements;

  private UnmodifiableArrayList(E[] elements) {
    this.elements = Objects.requireNonNull(elements, "elements");
  }

  public static <E> UnmodifiableArrayList<E> of(E... elements) {
    return new UnmodifiableArrayList<>(elements);
  }

  @Override public E get(int index) {
    return elements[index];
  }

  @Override public int size() {
    return elements.length;
  }
}