    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
    028 * to obtain information about a specific node object, a so-called
    029 * {@code NodeHandler} is used. The handler provides a number of methods for
    030 * querying the internal state of a node in a read-only way.
    031 * </p>
    032 *
    033 * @param <T> the type of the nodes this handler deals with
    034 */
    035public interface NodeHandler<T>
    036{
    037    /**
    038     * Returns the name of the specified node
    039     *
    040     * @param node the node
    041     * @return the name of this node
    042     */
    043    String nodeName(T node);
    044
    045    /**
    046     * Returns the value of the specified node.
    047     *
    048     * @param node the node
    049     * @return the value of this node
    050     */
    051    Object getValue(T node);
    052
    053    /**
    054     * Returns the parent of the specified node.
    055     *
    056     * @param node the node
    057     * @return the parent node
    058     */
    059    T getParent(T node);
    060
    061    /**
    062     * Returns an unmodifiable list with all children of the specified node.
    063     *
    064     * @param node the node
    065     * @return a list with the child nodes of this node
    066     */
    067    List<T> getChildren(T node);
    068
    069    /**
    070     * Returns an unmodifiable list of all children of the specified node with
    071     * 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     * Returns an unmodifiable list of all children of the specified node which
    081     * are matched by the passed in {@code NodeMatcher} against the provided
    082     * criterion. This method allows for advanced queries on a node's children.
    083     *
    084     * @param node the node
    085     * @param matcher the {@code NodeMatcher} defining filter criteria
    086     * @param criterion the criterion to be matched against; this object is
    087     *        passed to the {@code NodeMatcher}
    088     * @param <C> the type of the criterion
    089     * @return a list with all children matched by the matcher
    090     */
    091    <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);
    092
    093    /**
    094     * Returns the child with the given index of the specified node.
    095     *
    096     * @param node the node
    097     * @param index the index (0-based)
    098     * @return the child with the given index
    099     */
    100    T getChild(T node, int index);
    101
    102    /**
    103     * Returns the index of the given child node in the list of children of its
    104     * parent. This method is the opposite operation of
    105     * {@link #getChild(Object, int)}. This method returns 0 if the given node
    106     * is the first child node with this name, 1 for the second child node and
    107     * so on. If the node has no parent node or if it is an attribute, -1 is
    108     * returned.
    109     *
    110     * @param parent the parent node
    111     * @param child a child node whose index is to be retrieved
    112     * @return the index of this child node
    113     */
    114    int indexOfChild(T parent, T child);
    115
    116    /**
    117     * Returns the number of children of the specified node with the given name.
    118     * This method exists for performance reasons: for some node implementations
    119     * it may be by far more efficient to count the children than to query a
    120     * list of all children and determine its size. A concrete implementation
    121     * can choose the most efficient way to determine the number of children. If
    122     * a child name is passed in, only the children with this name are taken
    123     * into account. If the name <b>null</b> is passed, the total number of
    124     * children must be returned.
    125     *
    126     * @param node the node
    127     * @param name the name of the children in question (can be <b>null</b> for
    128     *        all children)
    129     * @return the number of the selected children
    130     */
    131    int getChildrenCount(T node, String name);
    132
    133    /**
    134     * Returns the number of children of the specified node which are matched by
    135     * the given {@code NodeMatcher}. This is a more generic version of
    136     * {@link #getChildrenCount(Object, String)}. It allows checking for
    137     * arbitrary filter conditions.
    138     *
    139     * @param node the node
    140     * @param matcher the {@code NodeMatcher}
    141     * @param criterion the criterion to be passed to the {@code NodeMatcher}
    142     * @param <C> the type of the criterion
    143     * @return the number of matched children
    144     */
    145    <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);
    146
    147    /**
    148     * Returns an unmodifiable set with the names of all attributes of the
    149     * specified node.
    150     *
    151     * @param node the node
    152     * @return a set with the names of all attributes of this node
    153     */
    154    Set<String> getAttributes(T node);
    155
    156    /**
    157     * Returns a flag whether the passed in node has any attributes.
    158     *
    159     * @param node the node
    160     * @return a flag whether this node has any attributes
    161     */
    162    boolean hasAttributes(T node);
    163
    164    /**
    165     * Returns the value of the specified attribute from the given node. If a
    166     * concrete {@code NodeHandler} supports attributes with multiple values,
    167     * result might be a collection.
    168     *
    169     * @param node the node
    170     * @param name the name of the attribute
    171     * @return the value of this attribute
    172     */
    173    Object getAttributeValue(T node, String name);
    174
    175    /**
    176     * Checks whether the specified node is defined. Nodes are
    177     * &quot;defined&quot; if they contain any data, e.g. a value, or
    178     * attributes, or defined children.
    179     *
    180     * @param node the node to test
    181     * @return a flag whether the passed in node is defined
    182     */
    183    boolean isDefined(T node);
    184
    185    /**
    186     * Returns the root node of the underlying hierarchy.
    187     *
    188     * @return the current root node
    189     */
    190    T getRootNode();
    191}