Java tutorial
/* * Copyright 2013 The Netty Project * * The Netty Project 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 io.netty.util.internal; import io.netty.util.internal.ObjectPool.Handle; import io.netty.util.internal.ObjectPool.ObjectCreator; import java.util.ArrayList; import java.util.Collection; import java.util.List; import java.util.RandomAccess; /** * A simple list which is recyclable. This implementation does not allow {@code null} elements to be added. */ public final class RecyclableArrayList extends ArrayList<Object> { private static final long serialVersionUID = -8605125654176467947L; private static final int DEFAULT_INITIAL_CAPACITY = 8; private static final ObjectPool<RecyclableArrayList> RECYCLER = ObjectPool .newPool(new ObjectCreator<RecyclableArrayList>() { @Override public RecyclableArrayList newObject(Handle<RecyclableArrayList> handle) { return new RecyclableArrayList(handle); } }); private boolean insertSinceRecycled; /** * Create a new empty {@link RecyclableArrayList} instance */ public static RecyclableArrayList newInstance() { return newInstance(DEFAULT_INITIAL_CAPACITY); } /** * Create a new empty {@link RecyclableArrayList} instance with the given capacity. */ public static RecyclableArrayList newInstance(int minCapacity) { RecyclableArrayList ret = RECYCLER.get(); ret.ensureCapacity(minCapacity); return ret; } private final Handle<RecyclableArrayList> handle; private RecyclableArrayList(Handle<RecyclableArrayList> handle) { this(handle, DEFAULT_INITIAL_CAPACITY); } private RecyclableArrayList(Handle<RecyclableArrayList> handle, int initialCapacity) { super(initialCapacity); this.handle = handle; } @Override public boolean addAll(Collection<?> c) { checkNullElements(c); if (super.addAll(c)) { insertSinceRecycled = true; return true; } return false; } @Override public boolean addAll(int index, Collection<?> c) { checkNullElements(c); if (super.addAll(index, c)) { insertSinceRecycled = true; return true; } return false; } private static void checkNullElements(Collection<?> c) { if (c instanceof RandomAccess && c instanceof List) { // produce less garbage List<?> list = (List<?>) c; int size = list.size(); for (int i = 0; i < size; i++) { if (list.get(i) == null) { throw new IllegalArgumentException("c contains null values"); } } } else { for (Object element : c) { if (element == null) { throw new IllegalArgumentException("c contains null values"); } } } } @Override public boolean add(Object element) { if (super.add(ObjectUtil.checkNotNull(element, "element"))) { insertSinceRecycled = true; return true; } return false; } @Override public void add(int index, Object element) { super.add(index, ObjectUtil.checkNotNull(element, "element")); insertSinceRecycled = true; } @Override public Object set(int index, Object element) { Object old = super.set(index, ObjectUtil.checkNotNull(element, "element")); insertSinceRecycled = true; return old; } /** * Returns {@code true} if any elements where added or set. This will be reset once {@link #recycle()} was called. */ public boolean insertSinceRecycled() { return insertSinceRecycled; } /** * Clear and recycle this instance. */ public boolean recycle() { clear(); insertSinceRecycled = false; handle.recycle(this); return true; } }