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 * 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
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 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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package org.apache.commons.configuration2;

import java.util.Collection;
import java.util.Map;

import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
import org.apache.commons.configuration2.interpol.Lookup;
import org.apache.commons.configuration2.sync.SynchronizerSupport;


The main Configuration interface.
This interface allows accessing and manipulating a configuration object. The major part of the methods defined in this interface deals with accessing properties of various data types. There is a generic getProperty() method, which returns the value of the queried property in its raw data type. Other getter methods try to convert this raw data type into a specific data type. If this fails, a ConversionException will be thrown.
For most of the property getter methods an overloaded version exists that allows to specify a default value, which will be returned if the queried property cannot be found in the configuration. The behavior of the methods that do not take a default value in case of a missing property is not defined by this interface and depends on a concrete implementation. E.g. the AbstractConfiguration class, which is the base class of most configuration implementations provided by this package, per default returns null if a property is not found, but provides the 
setThrowExceptionOnMissing() method, with which it can be configured to throw a NoSuchElementException exception in that case. (Note that getter methods for primitive types in AbstractConfiguration always throw an exception for missing properties because there is no way of overloading the return value.)
With the addProperty() and setProperty() methods new properties can be added to a configuration or the values of properties can be changed. With clearProperty() a property can be removed. Other methods allow to iterate over the contained properties or to create a subset configuration.
/**
 * <p>The main Configuration interface.</p>
 * <p>This interface allows accessing and manipulating a configuration object.
 * The major part of the methods defined in this interface deals with accessing
 * properties of various data types. There is a generic {@code getProperty()}
 * method, which returns the value of the queried property in its raw data
 * type. Other getter methods try to convert this raw data type into a specific
 * data type. If this fails, a {@code ConversionException} will be thrown.</p>
 * <p>For most of the property getter methods an overloaded version exists that
 * allows to specify a default value, which will be returned if the queried
 * property cannot be found in the configuration. The behavior of the methods
 * that do not take a default value in case of a missing property is not defined
 * by this interface and depends on a concrete implementation. E.g. the
 * {@link AbstractConfiguration} class, which is the base class
 * of most configuration implementations provided by this package, per default
 * returns <b>null</b> if a property is not found, but provides the
 * {@link AbstractConfiguration#setThrowExceptionOnMissing(boolean)
 * setThrowExceptionOnMissing()}
 * method, with which it can be configured to throw a {@code NoSuchElementException}
 * exception in that case. (Note that getter methods for primitive types in
 * {@code AbstractConfiguration} always throw an exception for missing
 * properties because there is no way of overloading the return value.)</p>
 * <p>With the {@code addProperty()} and {@code setProperty()} methods
 * new properties can be added to a configuration or the values of properties
 * can be changed. With {@code clearProperty()} a property can be removed.
 * Other methods allow to iterate over the contained properties or to create
 * a subset configuration.</p>
 *
 */
public interface Configuration extends ImmutableConfiguration, SynchronizerSupport
{
    
Return a decorator Configuration containing every key from the current
Configuration that starts with the specified prefix. The prefix is
removed from the keys in the subset. For example, if the configuration
contains the following properties:
   prefix.number = 1
   prefix.string = Apache
   prefixed.foo = bar
   prefix = Jakarta
 the Configuration returned by subset("prefix") will contain the properties: 
   number = 1
   string = Apache
   = Jakarta
(The key for the value "Jakarta" is an empty string)

Since the subset is a decorator and not a modified copy of the initial
Configuration, any change made to the subset is available to the
Configuration, and reciprocally.
Params:
prefix – The prefix used to select the properties.
See Also:
SubsetConfiguration
Returns:
a subset configuration/**
     * Return a decorator Configuration containing every key from the current
     * Configuration that starts with the specified prefix. The prefix is
     * removed from the keys in the subset. For example, if the configuration
     * contains the following properties:
     *
     * <pre>
     *    prefix.number = 1
     *    prefix.string = Apache
     *    prefixed.foo = bar
     *    prefix = Jakarta</pre>
     *
     * the Configuration returned by {@code subset("prefix")} will contain
     * the properties:
     *
     * <pre>
     *    number = 1
     *    string = Apache
     *    = Jakarta</pre>
     *
     * (The key for the value "Jakarta" is an empty string)
     * <p>
     * Since the subset is a decorator and not a modified copy of the initial
     * Configuration, any change made to the subset is available to the
     * Configuration, and reciprocally.
     *
     * @param prefix The prefix used to select the properties.
     * @return a subset configuration
     *
     * @see SubsetConfiguration
     */
    Configuration subset(String prefix);

    
Add a property to the configuration. If it already exists then the value
stated here will be added to the configuration entry. For example, if
the property:
resource.loader = file
is already present in the configuration and you call
addProperty("resource.loader", "classpath")
Then you will end up with a List like the following:
["file", "classpath"]
Params:
key – The key to add the property to.
value – The value to add./**
     * Add a property to the configuration. If it already exists then the value
     * stated here will be added to the configuration entry. For example, if
     * the property:
     *
     * <pre>resource.loader = file</pre>
     *
     * is already present in the configuration and you call
     *
     * <pre>addProperty("resource.loader", "classpath")</pre>
     *
     * Then you will end up with a List like the following:
     *
     * <pre>["file", "classpath"]</pre>
     *
     * @param key The key to add the property to.
     * @param value The value to add.
     */
    void addProperty(String key, Object value);

    
Set a property, this will replace any previously set values. Set values
is implicitly a call to clearProperty(key), addProperty(key, value).
Params:
key – The key of the property to change
value – The new value/**
     * Set a property, this will replace any previously set values. Set values
     * is implicitly a call to clearProperty(key), addProperty(key, value).
     *
     * @param key The key of the property to change
     * @param value The new value
     */
    void setProperty(String key, Object value);

    
Remove a property from the configuration.
Params:
key – the key to remove along with corresponding value./**
     * Remove a property from the configuration.
     *
     * @param key the key to remove along with corresponding value.
     */
    void clearProperty(String key);

    
Remove all properties from the configuration.
/**
     * Remove all properties from the configuration.
     */
    void clear();

    
Returns the ConfigurationInterpolator object used by this Configuration. This object is responsible for variable substitution. 
Returns:
the ConfigurationInterpolator (can be null)/**
     * Returns the {@code ConfigurationInterpolator} object used by this
     * {@code Configuration}. This object is responsible for variable
     * substitution.
     *
     * @return the {@code ConfigurationInterpolator} (can be <b>null</b>)
     */
    ConfigurationInterpolator getInterpolator();

    
Sets the ConfigurationInterpolator object to be used by this Configuration. This object is invoked for each access of a string property in order to substitute variables which may be contained. The argument can be null to disable interpolation at all.
Params:
ci – the new ConfigurationInterpolator/**
     * Sets the {@code ConfigurationInterpolator} object to be used by this
     * {@code Configuration}. This object is invoked for each access of a string
     * property in order to substitute variables which may be contained. The
     * argument can be <b>null</b> to disable interpolation at all.
     *
     * @param ci the new {@code ConfigurationInterpolator}
     */
    void setInterpolator(ConfigurationInterpolator ci);

    
Creates and installs a new ConfigurationInterpolator for this Configuration based on the passed in arguments. This method creates a default ConfigurationInterpolator instance and initializes it with the passed in Lookup objects. It also adds a special default Lookup object that tries to resolve variables by matching them with properties contained in this Configuration. This is also the main difference to the setInterpolator(ConfigurationInterpolator) method which sets the passed in object as is without adding this special lookup. 
Params:
prefixLookups – the map with Lookup objects associated with specific prefixes (can be null)
defLookups – a collection with default Lookup objects (can be null)
See Also:
ConfigurationInterpolator/**
     * Creates and installs a new {@code ConfigurationInterpolator} for this
     * {@code Configuration} based on the passed in arguments. This method
     * creates a default {@code ConfigurationInterpolator} instance and
     * initializes it with the passed in {@code Lookup} objects. It also adds a
     * special default {@code Lookup} object that tries to resolve variables by
     * matching them with properties contained in this {@code Configuration}.
     * This is also the main difference to the
     * {@link #setInterpolator(ConfigurationInterpolator)} method
     * which sets the passed in object as is without adding this special lookup.
     *
     * @param prefixLookups the map with {@code Lookup} objects associated with
     *        specific prefixes (can be <b>null</b>)
     * @param defLookups a collection with default {@code Lookup} objects (can
     *        be <b>null</b>)
     * @see ConfigurationInterpolator
     */
    void installInterpolator(Map<String, ? extends Lookup> prefixLookups,
            Collection<? extends Lookup> defLookups);
}