org.apache.commons.configuration.tree
Class NodeCombiner

java.lang.Object
  org.apache.commons.configuration.tree.NodeCombiner

Direct Known Subclasses:

OverrideCombiner, UnionCombiner

public abstract class NodeCombiner
extends Object

A base class for node combiner implementations.

A node combiner is an object that knows how two hierarchical node structures can be combined into a single one. Of course, there are many possible ways of implementing such a combination, e.g. constructing a union, an intersection, or an "override" structure (were nodes in the first hierarchy take precedence over nodes in the second hierarchy). This abstract base class only provides some helper methods and defines the common interface for node combiners. Concrete sub classes will implement the diverse combination algorithms.

For some concrete combiner implementations it is important to distinguish whether a node is a single node or whether it belongs to a list structure. Alone from the input structures, the combiner will not always be able to make this decision. So sometimes it may be necessary for the developer to configure the combiner and tell it, which nodes should be treated as list nodes. For this purpose the addListNode() method exists. It can be passed the name of a node, which should be considered a list node.

Since:

1.3

Version:

$Id: NodeCombiner.java 561230 2007-07-31 04:17:09Z rahul $

Author:

Commons Configuration team

Field Summary

protected Set

listNodes Stores a list with node names that are known to be list nodes.

Constructor Summary

NodeCombiner()
Creates a new instance of NodeCombiner.

Method Summary

void	addListNode(String nodeName) Adds the name of a node to the list of known list nodes.
abstract ConfigurationNode	combine(ConfigurationNode node1, ConfigurationNode node2) Combines the hierarchies represented by the given root nodes.
protected ViewNode	createViewNode() Creates a new view node.
Set	getListNodes() Returns a set with the names of nodes that are known to be list nodes.
boolean	isListNode(ConfigurationNode node) Checks if a node is a list node.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

listNodes

protected Set listNodes

Stores a list with node names that are known to be list nodes.

Constructor Detail

NodeCombiner

public NodeCombiner()

Creates a new instance of NodeCombiner.

Method Detail

addListNode

public void addListNode(String nodeName)

Adds the name of a node to the list of known list nodes. This means that nodes with this name will never be combined.

Parameters:

nodeName - the name to be added

getListNodes

public Set getListNodes()

Returns a set with the names of nodes that are known to be list nodes.

Returns:

a set with the names of list nodes

isListNode

public boolean isListNode(ConfigurationNode node)

Checks if a node is a list node. This implementation tests if the given node name is contained in the set of known list nodes. Derived classes which use different criteria may overload this method.

Parameters:

node - the node to be tested

Returns:

a flag whether this is a list node

combine

public abstract ConfigurationNode combine(ConfigurationNode node1,
                                          ConfigurationNode node2)

Combines the hierarchies represented by the given root nodes. This method must be defined in concrete sub classes with the implementation of a specific combination algorithm.

Parameters:

node1 - the first root node

node2 - the second root node

Returns:

the resulting combined node structure

createViewNode

protected ViewNode createViewNode()

Creates a new view node. This method will be called whenever a new view node is to be created. It can be overriden to create special view nodes. This base implementation returns a new instance of ViewNode.

Returns:

the new view node