    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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns 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     * Returns the root node of the underlying hierarchy.
    172     *
    173     * @return the current root node
    174     */
    175    T getRootNode();
    176}