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 *     https://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    /**
037     * Gets an unmodifiable set with the names of all attributes of the specified node.
038     *
039     * @param node the node
040     * @return a set with the names of all attributes of this node
041     */
042    Set<String> getAttributes(T node);
043
044    /**
045     * Gets the value of the specified attribute from the given node. If a concrete {@code NodeHandler} supports
046     * attributes with multiple values, result might be a collection.
047     *
048     * @param node the node
049     * @param name the name of the attribute
050     * @return the value of this attribute
051     */
052    Object getAttributeValue(T node, String name);
053
054    /**
055     * Gets the child with the given index of the specified node.
056     *
057     * @param node the node
058     * @param index the index (0-based)
059     * @return the child with the given index
060     */
061    T getChild(T node, int index);
062
063    /**
064     * Gets an unmodifiable list with all children of the specified node.
065     *
066     * @param node the node
067     * @return a list with the child nodes of this node
068     */
069    List<T> getChildren(T node);
070
071    /**
072     * Gets an unmodifiable list of all children of the specified node with the given name.
073     *
074     * @param node the node
075     * @param name the name of the desired child nodes
076     * @return a list with all children with the given name
077     */
078    List<T> getChildren(T node, String name);
079
080    /**
081     * Gets the number of children of the specified node with the given name. This method exists for performance reasons:
082     * for some node implementations it may be by far more efficient to count the children than to query a list of all
083     * children and determine its size. A concrete implementation can choose the most efficient way to determine the number
084     * of children. If a child name is passed in, only the children with this name are taken into account. If the name
085     * <strong>null</strong> is passed, the total number of children must be returned.
086     *
087     * @param node the node
088     * @param name the name of the children in question (can be <strong>null</strong> for all children)
089     * @return the number of the selected children
090     */
091    int getChildrenCount(T node, String name);
092
093    /**
094     * Gets an unmodifiable list of all children of the specified node which are matched by the passed in
095     * {@code NodeMatcher} against the provided criterion. This method allows for advanced queries on a node's children.
096     *
097     * @param node the node
098     * @param matcher the {@code NodeMatcher} defining filter criteria
099     * @param criterion the criterion to be matched against; this object is passed to the {@code NodeMatcher}
100     * @param <C> the type of the criterion
101     * @return a list with all children matched by the matcher
102     */
103    <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
104
105    /**
106     * Gets the number of children of the specified node which are matched by the given {@code NodeMatcher}. This is a
107     * more generic version of {@link #getChildrenCount(Object, String)}. It allows checking for arbitrary filter
108     * conditions.
109     *
110     * @param node the node
111     * @param matcher the {@code NodeMatcher}
112     * @param criterion the criterion to be passed to the {@code NodeMatcher}
113     * @param <C> the type of the criterion
114     * @return the number of matched children
115     */
116    <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
117
118    /**
119     * Gets the parent of the specified node.
120     *
121     * @param node the node
122     * @return the parent node
123     */
124    T getParent(T node);
125
126    /**
127     * Gets the root node of the underlying hierarchy.
128     *
129     * @return the current root node
130     */
131    T getRootNode();
132
133    /**
134     * Gets the value of the specified node.
135     *
136     * @param node the node
137     * @return the value of this node
138     */
139    Object getValue(T node);
140
141    /**
142     * Returns a flag whether the passed in node has any attributes.
143     *
144     * @param node the node
145     * @return a flag whether this node has any attributes
146     */
147    boolean hasAttributes(T node);
148
149    /**
150     * Returns the index of the given child node in the list of children of its parent. This method is the opposite
151     * operation of {@link #getChild(Object, int)}. This method returns 0 if the given node is the first child node with
152     * 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
153     * returned.
154     *
155     * @param parent the parent node
156     * @param child a child node whose index is to be retrieved
157     * @return the index of this child node
158     */
159    int indexOfChild(T parent, T child);
160
161    /**
162     * Checks whether the specified node is defined. Nodes are &quot;defined&quot; if they contain any data, for example a value,
163     * or attributes, or defined children.
164     *
165     * @param node the node to test
166     * @return a flag whether the passed in node is defined
167     */
168    boolean isDefined(T node);
169
170    /**
171     * Returns the name of the specified node
172     *
173     * @param node the node
174     * @return the name of this node
175     */
176    String nodeName(T node);
177}