    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}