001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.tree;
018
019import java.util.List;
020import java.util.Set;
021
022/**
023 * <p>
024 * Definition of an interface for accessing the data of a configuration node.
025 * </p>
026 * <p>
027 * Hierarchical configurations can deal with arbitrary node structures. In order to obtain information about a specific
028 * node object, a so-called {@code NodeHandler} is used. The handler provides a number of methods for querying the
029 * internal state of a node in a read-only way.
030 * </p>
031 *
032 * @param <T> the type of the nodes this handler deals with
033 */
034public interface NodeHandler<T> {
035    /**
036     * Gets an unmodifiable set with the names of all attributes of the specified node.
037     *
038     * @param node the node
039     * @return a set with the names of all attributes of this node
040     */
041    Set<String> getAttributes(T node);
042
043    /**
044     * Gets the value of the specified attribute from the given node. If a concrete {@code NodeHandler} supports
045     * attributes with multiple values, result might be a collection.
046     *
047     * @param node the node
048     * @param name the name of the attribute
049     * @return the value of this attribute
050     */
051    Object getAttributeValue(T node, String name);
052
053    /**
054     * Gets the child with the given index of the specified node.
055     *
056     * @param node the node
057     * @param index the index (0-based)
058     * @return the child with the given index
059     */
060    T getChild(T node, int index);
061
062    /**
063     * Gets an unmodifiable list with all children of the specified node.
064     *
065     * @param node the node
066     * @return a list with the child nodes of this node
067     */
068    List<T> getChildren(T node);
069
070    /**
071     * Gets an unmodifiable list of all children of the specified node with the given name.
072     *
073     * @param node the node
074     * @param name the name of the desired child nodes
075     * @return a list with all children with the given name
076     */
077    List<T> getChildren(T node, String name);
078
079    /**
080     * Gets the number of children of the specified node with the given name. This method exists for performance reasons:
081     * for some node implementations it may be by far more efficient to count the children than to query a list of all
082     * children and determine its size. A concrete implementation can choose the most efficient way to determine the number
083     * of children. If a child name is passed in, only the children with this name are taken into account. If the name
084     * <b>null</b> is passed, the total number of children must be returned.
085     *
086     * @param node the node
087     * @param name the name of the children in question (can be <b>null</b> for all children)
088     * @return the number of the selected children
089     */
090    int getChildrenCount(T node, String name);
091
092    /**
093     * Gets an unmodifiable list of all children of the specified node which are matched by the passed in
094     * {@code NodeMatcher} against the provided criterion. This method allows for advanced queries on a node's children.
095     *
096     * @param node the node
097     * @param matcher the {@code NodeMatcher} defining filter criteria
098     * @param criterion the criterion to be matched against; this object is passed to the {@code NodeMatcher}
099     * @param <C> the type of the criterion
100     * @return a list with all children matched by the matcher
101     */
102    <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
103
104    /**
105     * Gets the number of children of the specified node which are matched by the given {@code NodeMatcher}. This is a
106     * more generic version of {@link #getChildrenCount(Object, String)}. It allows checking for arbitrary filter
107     * conditions.
108     *
109     * @param node the node
110     * @param matcher the {@code NodeMatcher}
111     * @param criterion the criterion to be passed to the {@code NodeMatcher}
112     * @param <C> the type of the criterion
113     * @return the number of matched children
114     */
115    <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
116
117    /**
118     * Gets the parent of the specified node.
119     *
120     * @param node the node
121     * @return the parent node
122     */
123    T getParent(T node);
124
125    /**
126     * Gets the root node of the underlying hierarchy.
127     *
128     * @return the current root node
129     */
130    T getRootNode();
131
132    /**
133     * Gets the value of the specified node.
134     *
135     * @param node the node
136     * @return the value of this node
137     */
138    Object getValue(T node);
139
140    /**
141     * Returns a flag whether the passed in node has any attributes.
142     *
143     * @param node the node
144     * @return a flag whether this node has any attributes
145     */
146    boolean hasAttributes(T node);
147
148    /**
149     * Returns the index of the given child node in the list of children of its parent. This method is the opposite
150     * operation of {@link #getChild(Object, int)}. This method returns 0 if the given node is the first child node with
151     * this name, 1 for the second child node and so on. If the node has no parent node or if it is an attribute, -1 is
152     * returned.
153     *
154     * @param parent the parent node
155     * @param child a child node whose index is to be retrieved
156     * @return the index of this child node
157     */
158    int indexOfChild(T parent, T child);
159
160    /**
161     * Checks whether the specified node is defined. Nodes are &quot;defined&quot; if they contain any data, e.g. a value,
162     * or attributes, or defined children.
163     *
164     * @param node the node to test
165     * @return a flag whether the passed in node is defined
166     */
167    boolean isDefined(T node);
168
169    /**
170     * Returns the name of the specified node
171     *
172     * @param node the node
173     * @return the name of this node
174     */
175    String nodeName(T node);
176}