common/org.eclipse.tracecompass.common.core/src/org/eclipse/tracecompass/common/core/collect/StreamFlattener.java

   1 /*******************************************************************************
   2  * Copyright (c) 2015 EfficiOS Inc., Alexandre Montplaisir
   3  *
   4  * All rights reserved. This program and the accompanying materials
   5  * are made available under the terms of the Eclipse Public License v1.0
   6  * which accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *******************************************************************************/
   9
  10 package org.eclipse.tracecompass.common.core.collect;
  11
  12 import static org.eclipse.tracecompass.common.core.NonNullUtils.checkNotNull;
  13
  14 import java.util.function.Function;
  15 import java.util.stream.Stream;
  16
  17 /**
  18  * Generic utility class to "flatten" a data structure using the {@link Stream}
  19  * API.
  20  *
  21  * @author Alexandre Montplaisir
  22  *
  23  * @param <T>
  24  *            The type of container, or "node" in the tree
  25  * @since 2.0
  26  */
  27 public class StreamFlattener<T> {
  28
  29     private final Function<T, Stream<T>> fGetChildrenFunction;
  30
  31     /**
  32      * Constructor
  33      *
  34      * @param getChildrenFunction
  35      *            The function to use to get each element's children. Should
  36      *            return a {@link Stream} of those children.
  37      */
  38     public StreamFlattener(Function<T, Stream<T>> getChildrenFunction) {
  39         fGetChildrenFunction = getChildrenFunction;
  40     }
  41
  42     /**
  43      * Do an in-order flattening of the data structure, starting at the given
  44      * element (or node).
  45      *
  46      * @param element
  47      *            The tree node or similar from which to start
  48      * @return A unified Stream of all the children that were found,
  49      *         recursively.
  50      */
  51     public Stream<T> flatten(T element) {
  52         Stream<T> ret = Stream.concat(
  53                 Stream.of(element),
  54                 fGetChildrenFunction.apply(element).flatMap(this::flatten));
  55         return checkNotNull(ret);
  56     }
  57 }