FactoryPools类

android源码已经为我们提供了一个对象池。

Pools.java

public final class Pools {

    /**
     * Interface for managing a pool of objects.
     *
     * @param <T> The pooled type.
     */
    public static interface Pool<T> {

        /**
         * @return An instance from the pool if such, null otherwise.
         */
        @Nullable
        public T acquire();

        /**
         * Release an instance to the pool.
         *
         * @param instance The instance to release.
         * @return Whether the instance was put in the pool.
         *
         * @throws IllegalStateException If the instance is already in the pool.
         */
        public boolean release(@NonNull T instance);
    }

    private Pools() {
        /* do nothing - hiding constructor */
    }

    /**
     * Simple (non-synchronized) pool of objects.
     *
     * @param <T> The pooled type.
     */
    public static class SimplePool<T> implements Pool<T> {
        private final Object[] mPool;

        private int mPoolSize;

        /**
         * Creates a new instance.
         *
         * @param maxPoolSize The max pool size.
         *
         * @throws IllegalArgumentException If the max pool size is less than zero.
         */
        public SimplePool(int maxPoolSize) {
            if (maxPoolSize <= 0) {
                throw new IllegalArgumentException("The max pool size must be > 0");
            }
            mPool = new Object[maxPoolSize];
        }

        @Override
        @SuppressWarnings("unchecked")
        public T acquire() {
            if (mPoolSize > 0) {
                final int lastPooledIndex = mPoolSize - 1;
                T instance = (T) mPool[lastPooledIndex];
                mPool[lastPooledIndex] = null;
                mPoolSize--;
                return instance;
            }
            return null;
        }

        @Override
        public boolean release(@NonNull T instance) {
            if (isInPool(instance)) {
                throw new IllegalStateException("Already in the pool!");
            }
            if (mPoolSize < mPool.length) {
                mPool[mPoolSize] = instance;
                mPoolSize++;
                return true;
            }
            return false;
        }

        private boolean isInPool(@NonNull T instance) {
            for (int i = 0; i < mPoolSize; i++) {
                if (mPool[i] == instance) {
                    return true;
                }
            }
            return false;
        }
    }

    /**
     * Synchronized) pool of objects.
     *
     * @param <T> The pooled type.
     */
    public static class SynchronizedPool<T> extends SimplePool<T> {
        private final Object mLock = new Object();

        /**
         * Creates a new instance.
         *
         * @param maxPoolSize The max pool size.
         *
         * @throws IllegalArgumentException If the max pool size is less than zero.
         */
        public SynchronizedPool(int maxPoolSize) {
            super(maxPoolSize);
        }

        @Override
        public T acquire() {
            synchronized (mLock) {
                return super.acquire();
            }
        }

        @Override
        public boolean release(@NonNull T element) {
            synchronized (mLock) {
                return super.release(element);
            }
        }
    }
}

它是个逆向池，就是说，池子大小是固定的，但是池子是空的，如果直接去accquire()的话，则获取不到数据。池子中的数据是通过release()调用，不算加入到池子中的。

我觉得，这有个问题，就是池子中的每个对象可能都不一样，会打上使用者的烙印。

FactoryPools池

FactoryPools是在上面Pools的基础上进行的改造。

它相当于是个工具类，对外提供池子的接口：

• simple(int size, @NonNull Factory factory)：提供的是线程不安全的池子，对于性能要求高而不会出现数据冲突的
• threadSafe(int size, @NonNull Factory factory)：线程安全的池子
• threadSafeList()：List对象
• threadSafeList(int size)：List对象