android/guava/src/com/google/common/util/concurrent/CycleDetectingLockFactory.java
@VisibleForTesting
  static <E extends Enum<E>> Map<E, LockGraphNode> createNodes(Class<E> clazz) {
    EnumMap<E, LockGraphNode> map = Maps.newEnumMap(clazz);
    E[] keys = clazz.getEnumConstants();
    final int numKeys = keys.length;
    ArrayList<LockGraphNode> nodes = Lists.newArrayListWithCapacity(numKeys);
    // Create a LockGraphNode for each enum value.
    for (E key : keys) {
      LockGraphNode node = new LockGraphNode(getLockName(key));
      nodes.add(node);
      map.put(key, node);
    }
    // Pre-populate all allowedPriorLocks with nodes of smaller ordinal.
    for (int i = 1; i < numKeys; i++) {
      nodes.get(i).checkAcquiredLocks(Policies.THROW, nodes.subList(0, i));
    }
    // Pre-populate all disallowedPriorLocks with nodes of larger ordinal.
    for (int i = 0; i < numKeys - 1; i++) {
      nodes.get(i).checkAcquiredLocks(Policies.DISABLED, nodes.subList(i + 1, numKeys));
    }
    return Collections.unmodifiableMap(map);
  }
@VisibleForTesting
  static <E extends Enum<E>> Map<E, LockGraphNode> createNodes(Class<E> clazz) {
    EnumMap<E, LockGraphNode> map = Maps.newEnumMap(clazz);
    E[] keys = clazz.getEnumConstants();
    final int numKeys = keys.length;
    ArrayList<LockGraphNode> nodes = Lists.newArrayListWithCapacity(numKeys);
    // Create a LockGraphNode for each enum value.
    for (E key : keys) {
      LockGraphNode node = new LockGraphNode(getLockName(key));
      nodes.add(node);
      map.put(key, node);
    }
    // Pre-populate all allowedPriorLocks with nodes of smaller ordinal.
    for (int i = 1; i < numKeys; i++) {
      nodes.get(i).checkAcquiredLocks(Policies.THROW, nodes.subList(0, i));
    }
    // Pre-populate all disallowedPriorLocks with nodes of larger ordinal.
    for (int i = 0; i < numKeys - 1; i++) {
      nodes.get(i).checkAcquiredLocks(Policies.DISABLED, nodes.subList(i + 1, numKeys));
    }
    return Collections.unmodifiableMap(map);
  }
For a given Enum type, creates an immutable map from each of the Enum's values to a
corresponding LockGraphNode, with the {@code allowedPriorLocks} and {@code
disallowedPriorLocks} prepopulated with nodes according to the natural ordering of the
associated Enum values.