content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.collections;
  
  import com.google.common.base.Preconditions;
  
  import java.util.ArrayList;
  import java.util.List;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * A Directed Acyclic Graph (DAG) node.
   *
   * @param <T> payload
   */
  @NotThreadSafe
  public class DirectedAcyclicGraphNode<T> {
    private final T mPayload;
    private final List<DirectedAcyclicGraphNode<T>> mParents;
    private final List<DirectedAcyclicGraphNode<T>> mChildren;
  
    /**
     * A Directed Acyclic Graph (DAG) node.
     *
     * @param payload the payload of the node
     * @param parents the parents of the node
     * @param children the children of the node
     */
    public DirectedAcyclicGraphNode(T payload, List<DirectedAcyclicGraphNode<T>> parents,
        List<DirectedAcyclicGraphNode<T>> children) {
      mPayload = Preconditions.checkNotNull(payload, "payload");
      mParents = Preconditions.checkNotNull(parents, "parents");
      mChildren = Preconditions.checkNotNull(children, "children");
    }
  
    /**
     * A Directed Acyclic Graph (DAG) node.
     *
     * @param payload the payload of the node
     */
    public DirectedAcyclicGraphNode(T payload) {
      this(payload, new ArrayList<DirectedAcyclicGraphNode<T>>(),
        new ArrayList<DirectedAcyclicGraphNode<T>>());
    }
  
    /**
     * Gets the payload of the node.
     *
     * @return the payload of the node
     */
    public T getPayload() {
      return mPayload;
    }
  
    /**
     * Gets the parent nodes of the node.
     *
     * @return the parents of the node
     */
    public List<DirectedAcyclicGraphNode<T>> getParents() {
      return mParents;
    }
  
    /**
     * Gets the children nodes of the node.
     *
     * @return the children of the node
     */
    public List<DirectedAcyclicGraphNode<T>> getChildren() {
      return mChildren;
    }
  
    /**
     * Adds a parent node to the node.
     *
     * @param parent the node to be added as a parent
     */
    public void addParent(DirectedAcyclicGraphNode<T> parent) {
      mParents.add(parent);
    }
  
    /**
     * Adds a child node to the node.
     *
     * @param child the node to be added as a child
     */
    public void addChild(DirectedAcyclicGraphNode<T> child) {
      mChildren.add(child);
    }
  
    /**
     * Removes a child node from the node.
     *
     * @param child the child node to be removed
     */
    public void removeChild(DirectedAcyclicGraphNode<T> child) {
      Preconditions.checkState(mChildren.contains(child));
      mChildren.remove(child);
    }
  }
  