Add a general-purpose tree node data structure

This will come in handy for the ImageJ-OMERO project's ROI support.

Author: ctrueden

pom.xml

@@ -10,7 +10,7 @@
 	</parent>
 
 	<artifactId>scijava-common</artifactId>
-	<version>2.72.1-SNAPSHOT</version>
+	<version>2.73.0-SNAPSHOT</version>
 
 	<name>SciJava Common</name>
 	<description>SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.</description>

src/main/java/org/scijava/util/DefaultTreeNode.java

@@ -0,0 +1,82 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
+ * Institute of Molecular Cell Biology and Genetics, University of
+ * Konstanz, and KNIME GmbH.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.util;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Default implementation of {@link TreeNode}.
+ *
+ * @author Alison Walter
+ * @param <T> type of data associated with the node
+ */
+public class DefaultTreeNode<T> implements TreeNode<T> {
+
+	private TreeNode<?> parent;
+	private final List<TreeNode<?>> children;
+	private final T data;
+
+	/**
+	 * Creates a new tree node wrapping the given data, located in the tree
+	 * beneath the specified parent.
+	 * 
+	 * @param data The data to wrap.
+	 * @param parent The parent node of the tree.
+	 */
+	public DefaultTreeNode(final T data, final TreeNode<?> parent) {
+		this.data = data;
+		this.parent = parent;
+		children = new ArrayList<>();
+	}
+
+	@Override
+	public T data() {
+		return data;
+	}
+
+	@Override
+	public TreeNode<?> parent() {
+		return parent;
+	}
+
+	@Override
+	public void setParent(final TreeNode<?> parent) {
+		this.parent = parent;
+	}
+
+	@Override
+	public List<TreeNode<?>> children() {
+		return children;
+	}
+}

src/main/java/org/scijava/util/TreeNode.java

@@ -0,0 +1,67 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
+ * Institute of Molecular Cell Biology and Genetics, University of
+ * Konstanz, and KNIME GmbH.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.util;
+
+import java.util.List;
+
+/**
+ * A wrapper around a data object, for storing it in a tree structure.
+ *
+ * @author Alison Walter
+ * @param <T> type of data associated with the node
+ */
+public interface TreeNode<T> {
+
+	/** Gets the data associated with the node. */
+	T data();
+
+	/** Gets the parent of this node. */
+	TreeNode<?> parent();
+
+	void setParent(TreeNode<?> parent);
+
+	/**
+	 * Gets the node's children. If this list is mutated, the children will be
+	 * affected accordingly. It is the responsibility of the caller to ensure
+	 * continued integrity, particularly of parent linkages.
+	 */
+	List<TreeNode<?>> children();
+
+	/** Adds the given list of children to this node. */
+	default void addChildren(final List<? extends TreeNode<?>> nodes) {
+		for (final TreeNode<?> child : nodes) {
+			child.setParent(parent());
+		}
+		children().addAll(nodes);
+	}
+}