FastListソース分析

FastListは、HikariCPデータベース接続プールで使用されるカスタムリストです.実は特に何もありません.主にrange checkを消してデータを取るのがもっと速いです.
(1)クラス定義

public final class FastList extends ArrayList

ArrayListから引き継ぎ、
(2)メンバー変数

   private final Class> clazz;
   private T[] elementData;
   private int size;

clazz:listに格納されているデータ型class.
ElementData:データを格納するソース配列.
size:リストの現在のサイズ
(3)コンストラクタ

   @SuppressWarnings("unchecked")
   public FastList(Class> clazz)
   {
      this.elementData = (T[]) Array.newInstance(clazz, 32);
      this.clazz = clazz;
   }

   @SuppressWarnings("unchecked")
   public FastList(Class> clazz, int capacity)
   {
      this.elementData = (T[]) Array.newInstance(clazz, capacity);
      this.clazz = clazz;
   }

データ型と初期の配列容量を渡します.デフォルトの容量サイズは32で、sizeとは異なります.
(4)add要素の追加

@Override
   public boolean add(T element)
   {
      try {
         elementData[size++] = element;
      }
      catch (ArrayIndexOutOfBoundsException e) {
         // overflow-conscious code
         final int oldCapacity = elementData.length;
         final int newCapacity = oldCapacity << 1;
         @SuppressWarnings("unchecked")
         final T[] newElementData = (T[]) Array.newInstance(clazz, newCapacity);
         System.arraycopy(elementData, 0, newElementData, 0, oldCapacity);
         newElementData[size - 1] = element;
         elementData = newElementData;
      }

      return true;
   }

addメソッドを書き直しました.
配列に要素を挿入し、sizeを1増やし、配列が境界を越えている場合は、元の容量の2倍に拡張します.最後に、拡張された配列をソース配列に割り当てます.
(5)get指定された位置の要素を取得する

   @Override
   public T get(int index)
   {
      return elementData[index];
   }

getメソッドを書き直しました.
配列のindex下付きを直接取得し,境界を越えて異常を直接放出する.
(6)最後の要素を除去する

   public T removeLast()
   {
      T element = elementData[--size];
      elementData[size] = null;
      return element;
   }

size-1の位置要素を取り出し、空にし、sizeを1に減らします.
(7)指定した要素を除去する

   @Override
   public boolean remove(Object element)
   {
      for (int index = size - 1; index >= 0; index--) {
         if (element == elementData[index]) {
            final int numMoved = size - index - 1;
            if (numMoved > 0) {
               System.arraycopy(elementData, index + 1, elementData, index, numMoved);
            }
            elementData[--size] = null;
            return true;
         }
      }

      return false;
   }

配列の最后の面から前を探して、最初の同じ要素に出会った时に直接削除して、copyの元の配列、sizeは1を減らします.注意するのは、判断が等しいことが最も基本的な==であることです.
(8)すべての要素をクリア

@Override
   public void clear()
   {
      for (int i = 0; i < size; i++) {
         elementData[i] = null;
      }

      size = 0;
   }

最初から最後まで(size)を空に設定し、size=0にします.
(9)大きさを返し、空かどうかを判断し、多く言わない

 @Override
   public int size()
   {
      return size;
   }

   @Override
   public boolean isEmpty()
   {
      return size == 0;
   }

(10)最後にソースをそのまま貼り付けましょう

/*
 * Copyright (C) 2013, 2014 Brett Wooldridge
 *
 * Licensed 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 com.zaxxer.hikari.util;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;

/**
 * Fast list without range checking.
 *
 * @author Brett Wooldridge
 */
public final class FastList extends ArrayList
{
   private static final long serialVersionUID = -4598088075242913858L;

   private final Class> clazz;
   private T[] elementData;
   private int size;

   /**
    * Construct a FastList with a default size of 32.
    * @param clazz the Class stored in the collection
    */
   @SuppressWarnings("unchecked")
   public FastList(Class> clazz)
   {
      this.elementData = (T[]) Array.newInstance(clazz, 32);
      this.clazz = clazz;
   }

   /**
    * Construct a FastList with a specified size.
    * @param clazz the Class stored in the collection
    * @param capacity the initial size of the FastList
    */
   @SuppressWarnings("unchecked")
   public FastList(Class> clazz, int capacity)
   {
      this.elementData = (T[]) Array.newInstance(clazz, capacity);
      this.clazz = clazz;
   }

   /**
    * Add an element to the tail of the FastList.
    *
    * @param element the element to add
    */
   @Override
   public boolean add(T element)
   {
      try {
         elementData[size++] = element;
      }
      catch (ArrayIndexOutOfBoundsException e) {
         // overflow-conscious code
         final int oldCapacity = elementData.length;
         final int newCapacity = oldCapacity << 1;
         @SuppressWarnings("unchecked")
         final T[] newElementData = (T[]) Array.newInstance(clazz, newCapacity);
         System.arraycopy(elementData, 0, newElementData, 0, oldCapacity);
         newElementData[size - 1] = element;
         elementData = newElementData;
      }

      return true;
   }

   /**
    * Get the element at the specified index.
    *
    * @param index the index of the element to get
    * @return the element, or ArrayIndexOutOfBounds is thrown if the index is invalid
    */
   @Override
   public T get(int index)
   {
      return elementData[index];
   }

   /**
    * Remove the last element from the list.  No bound check is performed, so if this
    * method is called on an empty list and ArrayIndexOutOfBounds exception will be
    * thrown.
    *
    * @return the last element of the list
    */
   public T removeLast()
   {
      T element = elementData[--size];
      elementData[size] = null;
      return element;
   }

   /**
    * This remove method is most efficient when the element being removed
    * is the last element.  Equality is identity based, not equals() based.
    * Only the first matching element is removed.
    *
    * @param element the element to remove
    */
   @Override
   public boolean remove(Object element)
   {
      for (int index = size - 1; index >= 0; index--) {
         if (element == elementData[index]) {
            final int numMoved = size - index - 1;
            if (numMoved > 0) {
               System.arraycopy(elementData, index + 1, elementData, index, numMoved);
            }
            elementData[--size] = null;
            return true;
         }
      }

      return false;
   }

   /**
    * Clear the FastList.
    */
   @Override
   public void clear()
   {
      for (int i = 0; i < size; i++) {
         elementData[i] = null;
      }

      size = 0;
   }

   /**
    * Get the current number of elements in the FastList.
    *
    * @return the number of current elements
    */
   @Override
   public int size()
   {
      return size;
   }

   /** {@inheritDoc} */
   @Override
   public boolean isEmpty()
   {
      return size == 0;
   }

   /** {@inheritDoc} */
   @Override
   public T set(int index, T element)
   {
      T old = elementData[index];
      elementData[index] = element;
      return old;
   }

   /** {@inheritDoc} */
   @Override
   public T remove(int index)
   {
      if (size == 0) {
         return null;
      }

      final T old = elementData[index];

      final int numMoved = size - index - 1;
      if (numMoved > 0) {
         System.arraycopy(elementData, index + 1, elementData, index, numMoved);
      }

      elementData[--size] = null;

      return old;
   }

   /** {@inheritDoc} */
   @Override
   public boolean contains(Object o)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public Iterator iterator()
   {
      return new Iterator() {
         private int index;

         @Override
         public boolean hasNext()
         {
            return index < size;
         }

         @Override
         public T next()
         {
            if (index < size) {
               return elementData[index++];
            }

            throw new NoSuchElementException("No more elements in FastList"); 
         }
      };
   }

   /** {@inheritDoc} */
   @Override
   public Object[] toArray()
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public  E[] toArray(E[] a)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public boolean containsAll(Collection> c)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public boolean addAll(Collection extends T> c)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public boolean addAll(int index, Collection extends T> c)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public boolean removeAll(Collection> c)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public boolean retainAll(Collection> c)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public void add(int index, T element)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public int indexOf(Object o)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public int lastIndexOf(Object o)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public ListIterator listIterator()
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public ListIterator listIterator(int index)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public List subList(int fromIndex, int toIndex)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public void trimToSize()
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public void ensureCapacity(int minCapacity)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   public Object clone()
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   @Override
   protected void removeRange(int fromIndex, int toIndex)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   public void forEach(Consumer super T> action)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   public Spliterator spliterator()
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   public boolean removeIf(Predicate super T> filter)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   public void replaceAll(UnaryOperator operator)
   {
      throw new UnsupportedOperationException();
   }

   /** {@inheritDoc} */
   public void sort(Comparator super T> c)
   {
      throw new UnsupportedOperationException();
   }
}