src/android/src/com/google/android/inputmethod/japanese/view/WeakDrawableCache.java

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package org.mozc.android.inputmethod.japanese.view;

import com.google.common.base.Optional;
import com.google.common.base.Preconditions;

import android.graphics.drawable.Drawable;
import android.util.SparseArray;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;

/**
 * Simple cache implementation of {@code Drawable}.
 * This class uses WeakReference mechanism. So, drawables in this instance will be
 * released when gc runs and there are no strong references for them.
 *
 */
public class WeakDrawableCache {

  private static class WeakEntry extends WeakReference<Drawable> {

    final Integer key;
    WeakEntry(Integer key, Drawable value, ReferenceQueue<? super Drawable> queue) {
      super(value, queue);
      this.key = key;
    }
  }

  private final ReferenceQueue<Drawable> queue = new ReferenceQueue<Drawable>();
  private final SparseArray<WeakEntry> map = new SparseArray<WeakEntry>(128);

  private void cleanUp() {
    while (true) {
      WeakEntry reference = WeakEntry.class.cast(queue.poll());
      if (reference == null) {
        return;
      }
      map.remove(reference.key);
    }
  }

  /**
   * Put the {@code drawable} to this cache whose resource id is {@code key}.
   */
  public void put(Integer key, Drawable value) {
    Preconditions.checkNotNull(key);
    Preconditions.checkNotNull(value);
    cleanUp();
    map.put(key, new WeakEntry(key, value, queue));
  }

  /**
   * Returns {@code Drawable} instance for the {@code key}, or {@code null} if this doesn't
   * contain the corresponding {@code Drawable}.
   */
  public Optional<Drawable> get(Integer key) {
    cleanUp();
    WeakEntry entry = map.get(Preconditions.checkNotNull(key));
    // entry.get() may return null.
    return Optional.fromNullable(entry == null ? null : entry.get());
  }

  /**
   * Clears the cache content.
   */
  public void clear() {
    map.clear();

    // Clear the queue.
    while (true) {
      if (queue.poll() == null) {
        break;
      }
    }
  }
}