    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     * 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     * <strong>null</strong> 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 <strong>null</strong> 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, for example 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}