core/src/main/java/org/apache/accumulo/core/util/PreAllocatedArray.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.accumulo.core.util;

import java.util.ArrayList;
import java.util.Iterator;

import com.google.common.collect.Iterators;

/**
 * An {@link ArrayList} implementation that represents a type-safe pre-allocated array. This should
 * be used exactly like an array, but helps avoid type-safety issues when mixing arrays with
 * generics. The iterator is unmodifiable.
 */
public class PreAllocatedArray<T> implements Iterable<T> {

  private final ArrayList<T> internal;
  public final int length;

  /**
   * Creates an instance of the given capacity, with all elements initialized to null
   */
  public PreAllocatedArray(final int capacity) {
    length = capacity;
    internal = new ArrayList<>(capacity);
    for (int i = 0; i < capacity; i++) {
      internal.add(null);
    }
  }

  /**
   * Set the element at the specified index, and return the old value.
   */
  public T set(final int index, final T element) {
    return internal.set(index, element);
  }

  /**
   * Get the item stored at the specified index.
   */
  public T get(final int index) {
    return internal.get(index);
  }

  @Override
  public Iterator<T> iterator() {
    return Iterators.unmodifiableIterator(internal.iterator());
  }
}