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