MapIteratorHelper.java

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

package com.facebook.jni;

import javax.annotation.Nullable;

import java.util.Iterator;
import java.util.Map;

import com.facebook.proguard.annotations.DoNotStrip;

/**
 * To iterate over a Map from C++ requires four calls per entry: hasNext(),
 * next(), getKey(), getValue().  This helper reduces it to one call and two
 * field gets per entry.  It does not use a generic argument, since in C++, the
 * types will be erased, anyway.  This is *not* a {@link java.util.Iterator}.
 */
@DoNotStrip
public class MapIteratorHelper {
  @DoNotStrip private final Iterator<Map.Entry> mIterator;
  @DoNotStrip private @Nullable Object mKey;
  @DoNotStrip private @Nullable Object mValue;

  @DoNotStrip
  public MapIteratorHelper(Map map) {
    mIterator = map.entrySet().iterator();
  }

  /**
   * Moves the helper to the next entry in the map, if any.  Returns true iff
   * there is an entry to read.
   */
  @DoNotStrip
  boolean hasNext() {
    if (mIterator.hasNext()) {
      Map.Entry entry = mIterator.next();
      mKey = entry.getKey();
      mValue = entry.getValue();
      return true;
    } else {
      mKey = null;
      mValue = null;
      return false;
    }
  }
}