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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.apache.commons.configuration2.tree;

import java.util.List;
import java.util.Set;


Definition of an interface for accessing the data of a configuration node.

 Hierarchical configurations can deal with arbitrary node structures. In order to obtain information about a specific node object, a so-called NodeHandler is used. The handler provides a number of methods for querying the internal state of a node in a read-only way. 
Type parameters:
<T> – the type of the nodes this handler deals with/**
 * <p>
 * Definition of an interface for accessing the data of a configuration node.
 * </p>
 * <p>
 * Hierarchical configurations can deal with arbitrary node structures. In order
 * to obtain information about a specific node object, a so-called
 * {@code NodeHandler} is used. The handler provides a number of methods for
 * querying the internal state of a node in a read-only way.
 * </p>
 *
 * @param <T> the type of the nodes this handler deals with
 */
public interface NodeHandler<T>
{
    
Returns the name of the specified node
Params:
node – the node
Returns:
the name of this node/**
     * Returns the name of the specified node
     *
     * @param node the node
     * @return the name of this node
     */
    String nodeName(T node);

    
Returns the value of the specified node.
Params:
node – the node
Returns:
the value of this node/**
     * Returns the value of the specified node.
     *
     * @param node the node
     * @return the value of this node
     */
    Object getValue(T node);

    
Returns the parent of the specified node.
Params:
node – the node
Returns:
the parent node/**
     * Returns the parent of the specified node.
     *
     * @param node the node
     * @return the parent node
     */
    T getParent(T node);

    
Returns an unmodifiable list with all children of the specified node.
Params:
node – the node
Returns:
a list with the child nodes of this node/**
     * Returns an unmodifiable list with all children of the specified node.
     *
     * @param node the node
     * @return a list with the child nodes of this node
     */
    List<T> getChildren(T node);

    
Returns an unmodifiable list of all children of the specified node with
the given name.
Params:
node – the node
name – the name of the desired child nodes
Returns:
a list with all children with the given name/**
     * Returns an unmodifiable list of all children of the specified node with
     * the given name.
     *
     * @param node the node
     * @param name the name of the desired child nodes
     * @return a list with all children with the given name
     */
    List<T> getChildren(T node, String name);

    
Returns an unmodifiable list of all children of the specified node which are matched by the passed in NodeMatcher against the provided criterion. This method allows for advanced queries on a node's children. 
Params:
node – the node
matcher – the NodeMatcher defining filter criteria
criterion – the criterion to be matched against; this object is passed to the NodeMatcher
Type parameters:
<C> – the type of the criterion
Returns:
a list with all children matched by the matcher/**
     * Returns an unmodifiable list of all children of the specified node which
     * are matched by the passed in {@code NodeMatcher} against the provided
     * criterion. This method allows for advanced queries on a node's children.
     *
     * @param node the node
     * @param matcher the {@code NodeMatcher} defining filter criteria
     * @param criterion the criterion to be matched against; this object is
     *        passed to the {@code NodeMatcher}
     * @param <C> the type of the criterion
     * @return a list with all children matched by the matcher
     */
    <C> List<T> getMatchingChildren(T node, NodeMatcher<C> matcher, C criterion);

    
Returns the child with the given index of the specified node.
Params:
node – the node
index – the index (0-based)
Returns:
the child with the given index/**
     * Returns the child with the given index of the specified node.
     *
     * @param node the node
     * @param index the index (0-based)
     * @return the child with the given index
     */
    T getChild(T node, int index);

    
Returns the index of the given child node in the list of children of its parent. This method is the opposite operation of getChild(Object, int). This method returns 0 if the given node is the first child node with 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 returned. 
Params:
parent – the parent node
child – a child node whose index is to be retrieved
Returns:
the index of this child node/**
     * Returns the index of the given child node in the list of children of its
     * parent. This method is the opposite operation of
     * {@link #getChild(Object, int)}. This method returns 0 if the given node
     * is the first child node with 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
     * returned.
     *
     * @param parent the parent node
     * @param child a child node whose index is to be retrieved
     * @return the index of this child node
     */
    int indexOfChild(T parent, T child);

    
Returns the number of children of the specified node with the given name.
This method exists for performance reasons: for some node implementations
it may be by far more efficient to count the children than to query a
list of all children and determine its size. A concrete implementation
can choose the most efficient way to determine the number of children. If
a child name is passed in, only the children with this name are taken
into account. If the name null is passed, the total number of
children must be returned.
Params:
node – the node
name – the name of the children in question (can be null for
       all children)
Returns:
the number of the selected children/**
     * Returns the number of children of the specified node with the given name.
     * This method exists for performance reasons: for some node implementations
     * it may be by far more efficient to count the children than to query a
     * list of all children and determine its size. A concrete implementation
     * can choose the most efficient way to determine the number of children. If
     * a child name is passed in, only the children with this name are taken
     * into account. If the name <b>null</b> is passed, the total number of
     * children must be returned.
     *
     * @param node the node
     * @param name the name of the children in question (can be <b>null</b> for
     *        all children)
     * @return the number of the selected children
     */
    int getChildrenCount(T node, String name);

    
Returns the number of children of the specified node which are matched by the given NodeMatcher. This is a more generic version of getChildrenCount(Object, String). It allows checking for arbitrary filter conditions. 
Params:
node – the node
matcher – the NodeMatcher
criterion – the criterion to be passed to the NodeMatcher
Type parameters:
<C> – the type of the criterion
Returns:
the number of matched children/**
     * Returns the number of children of the specified node which are matched by
     * the given {@code NodeMatcher}. This is a more generic version of
     * {@link #getChildrenCount(Object, String)}. It allows checking for
     * arbitrary filter conditions.
     *
     * @param node the node
     * @param matcher the {@code NodeMatcher}
     * @param criterion the criterion to be passed to the {@code NodeMatcher}
     * @param <C> the type of the criterion
     * @return the number of matched children
     */
    <C> int getMatchingChildrenCount(T node, NodeMatcher<C> matcher, C criterion);

    
Returns an unmodifiable set with the names of all attributes of the
specified node.
Params:
node – the node
Returns:
a set with the names of all attributes of this node/**
     * Returns an unmodifiable set with the names of all attributes of the
     * specified node.
     *
     * @param node the node
     * @return a set with the names of all attributes of this node
     */
    Set<String> getAttributes(T node);

    
Returns a flag whether the passed in node has any attributes.
Params:
node – the node
Returns:
a flag whether this node has any attributes/**
     * Returns a flag whether the passed in node has any attributes.
     *
     * @param node the node
     * @return a flag whether this node has any attributes
     */
    boolean hasAttributes(T node);

    
Returns the value of the specified attribute from the given node. If a concrete NodeHandler supports attributes with multiple values, result might be a collection. 
Params:
node – the node
name – the name of the attribute
Returns:
the value of this attribute/**
     * Returns the value of the specified attribute from the given node. If a
     * concrete {@code NodeHandler} supports attributes with multiple values,
     * result might be a collection.
     *
     * @param node the node
     * @param name the name of the attribute
     * @return the value of this attribute
     */
    Object getAttributeValue(T node, String name);

    
Checks whether the specified node is defined. Nodes are
"defined" if they contain any data, e.g. a value, or
attributes, or defined children.
Params:
node – the node to test
Returns:
a flag whether the passed in node is defined/**
     * Checks whether the specified node is defined. Nodes are
     * &quot;defined&quot; if they contain any data, e.g. a value, or
     * attributes, or defined children.
     *
     * @param node the node to test
     * @return a flag whether the passed in node is defined
     */
    boolean isDefined(T node);

    
Returns the root node of the underlying hierarchy.
Returns:
the current root node/**
     * Returns the root node of the underlying hierarchy.
     *
     * @return the current root node
     */
    T getRootNode();
}