/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * 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
 * limitations under the License.
 */
package org.apache.commons.configuration2;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Properties;

The main interface for accessing configuration data in a read-only fashion.
 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.)
Since:
2.0/**
 * <p>The main interface for accessing configuration data in a read-only fashion.</p>
 * <p>
 * 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>
 *
 * @since 2.0
 */
public interface ImmutableConfiguration
{
    
Check if the configuration is empty.
Returns:
true if the configuration contains no property, false otherwise./**
     * Check if the configuration is empty.
     *
     * @return {@code true} if the configuration contains no property,
     *         {@code false} otherwise.
     */
    boolean isEmpty();

    
Returns the number of keys stored in this configuration. Note that a concrete implementation is not guaranteed to be efficient; for some implementations it may be expensive to determine the size. Especially, if you just want to check whether a configuration is empty, it is preferable to use the isEmpty() method. 
Returns:
the number of keys stored in this configuration/**
     * Returns the number of keys stored in this configuration. Note that a
     * concrete implementation is not guaranteed to be efficient; for some
     * implementations it may be expensive to determine the size. Especially, if
     * you just want to check whether a configuration is empty, it is preferable
     * to use the {@link #isEmpty()} method.
     *
     * @return the number of keys stored in this configuration
     */
    int size();

    
Check if the configuration contains the specified key.
Params:
key – the key whose presence in this configuration is to be tested
Returns:
true if the configuration contains a value for this key, false otherwise/**
     * Check if the configuration contains the specified key.
     *
     * @param key the key whose presence in this configuration is to be tested
     *
     * @return {@code true} if the configuration contains a value for this
     *         key, {@code false} otherwise
     */
    boolean containsKey(String key);

    
Gets a property from the configuration. This is the most basic get method for retrieving values of properties. In a typical implementation of the Configuration interface the other get methods (that return specific data types) will internally make use of this method. On this level variable substitution is not yet performed. The returned object is an internal representation of the property value for the passed in key. It is owned by the Configuration object. So a caller should not modify this object. It cannot be guaranteed that this object will stay constant over time (i.e. further update operations on the configuration may change its internal state). 
Params:
key – property to retrieve
Returns:
the value to which this configuration maps the specified key, or
        null if the configuration contains no mapping for this key./**
     * Gets a property from the configuration. This is the most basic get
     * method for retrieving values of properties. In a typical implementation
     * of the {@code Configuration} interface the other get methods (that
     * return specific data types) will internally make use of this method. On
     * this level variable substitution is not yet performed. The returned
     * object is an internal representation of the property value for the passed
     * in key. It is owned by the {@code Configuration} object. So a caller
     * should not modify this object. It cannot be guaranteed that this object
     * will stay constant over time (i.e. further update operations on the
     * configuration may change its internal state).
     *
     * @param key property to retrieve
     * @return the value to which this configuration maps the specified key, or
     *         null if the configuration contains no mapping for this key.
     */
    Object getProperty(String key);

    
Get the list of the keys contained in the configuration that match the
specified prefix. For instance, if the configuration contains the
following keys:
 db.user, db.pwd, db.url, window.xpos, window.ypos,
 an invocation of getKeys("db");

will return the keys below:
 db.user, db.pwd, db.url.

Note that the prefix itself is included in the result set if there is a
matching key. The exact behavior - how the prefix is actually
interpreted - depends on a concrete implementation.
Params:
prefix – The prefix to test against.
See Also:
getKeys()
Returns:
An Iterator of keys that match the prefix./**
     * Get the list of the keys contained in the configuration that match the
     * specified prefix. For instance, if the configuration contains the
     * following keys:<br>
     * {@code db.user, db.pwd, db.url, window.xpos, window.ypos},<br>
     * an invocation of {@code getKeys("db");}<br>
     * will return the keys below:<br>
     * {@code db.user, db.pwd, db.url}.<br>
     * Note that the prefix itself is included in the result set if there is a
     * matching key. The exact behavior - how the prefix is actually
     * interpreted - depends on a concrete implementation.
     *
     * @param prefix The prefix to test against.
     * @return An Iterator of keys that match the prefix.
     * @see #getKeys()
     */
    Iterator<String> getKeys(String prefix);

    
Get the list of the keys contained in the configuration. The returned iterator can be used to obtain all defined keys. It does not allow removing elements from this configuration via its remove() method. Note that the keys of this configuration are returned in a form, so that they can be directly evaluated; escaping of special characters (if necessary) has already been performed. 
Returns:
An Iterator./**
     * Get the list of the keys contained in the configuration. The returned
     * iterator can be used to obtain all defined keys. It does not allow
     * removing elements from this configuration via its {@code remove()}
     * method. Note that the keys of this configuration are returned in a form,
     * so that they can be directly evaluated; escaping of special characters
     * (if necessary) has already been performed.
     *
     * @return An Iterator.
     */
    Iterator<String> getKeys();

    
Get a list of properties associated with the given configuration key. This method expects the given key to have an arbitrary number of String values, each of which is of the form key=value. These strings are split at the equals sign, and the key parts will become keys of the returned Properties object, the value parts become values. 
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a String/List.
IllegalArgumentException – if one of the tokens is malformed (does not contain
an equals sign).
Returns:
The associated properties if key is found./**
     * Get a list of properties associated with the given configuration key. This method
     * expects the given key to have an arbitrary number of String values, each of which
     * is of the form {@code key=value}. These strings are split at the equals sign, and
     * the key parts will become keys of the returned {@code Properties} object, the value
     * parts become values.
     *
     * @param key The configuration key.
     * @return The associated properties if key is found.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a String/List.
     * @throws IllegalArgumentException if one of the tokens is malformed (does not contain
     * an equals sign).
     */
    Properties getProperties(String key);

    
Get a boolean associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Boolean.
Returns:
The associated boolean./**
     * Get a boolean associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated boolean.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Boolean.
     */
    boolean getBoolean(String key);

    
Get a boolean associated with the given configuration key. If the key doesn't map
to an existing object, the default value is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Boolean.
Returns:
The associated boolean./**
     * Get a boolean associated with the given configuration key. If the key doesn't map
     * to an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated boolean.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Boolean.
     */
    boolean getBoolean(String key, boolean defaultValue);

    
Get a Boolean associated with the given configuration key. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Boolean.
Returns:
The associated boolean if key is found and has valid format, default value
otherwise./**
     * Get a {@link Boolean} associated with the given configuration key.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated boolean if key is found and has valid format, default value
     * otherwise.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Boolean.
     */
    Boolean getBoolean(String key, Boolean defaultValue);

    
Get a byte associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Byte.
Returns:
The associated byte./**
     * Get a byte associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated byte.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Byte.
     */
    byte getByte(String key);

    
Get a byte associated with the given configuration key. If the key doesn't map to
an existing object, the default value is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Byte.
Returns:
The associated byte./**
     * Get a byte associated with the given configuration key. If the key doesn't map to
     * an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated byte.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Byte.
     */
    byte getByte(String key, byte defaultValue);

    
Get a Byte associated with the given configuration key. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Byte.
Returns:
The associated byte if key is found and has valid format, default value
otherwise./**
     * Get a {@link Byte} associated with the given configuration key.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated byte if key is found and has valid format, default value
     * otherwise.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Byte.
     */
    Byte getByte(String key, Byte defaultValue);

    
Get a double associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Double.
Returns:
The associated double./**
     * Get a double associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated double.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Double.
     */
    double getDouble(String key);

    
Get a double associated with the given configuration key. If the key doesn't map to
an existing object, the default value is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Double.
Returns:
The associated double./**
     * Get a double associated with the given configuration key. If the key doesn't map to
     * an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated double.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Double.
     */
    double getDouble(String key, double defaultValue);

    
Get a Double associated with the given configuration key. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Double.
Returns:
The associated double if key is found and has valid format, default value
otherwise./**
     * Get a {@link Double} associated with the given configuration key.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated double if key is found and has valid format, default value
     * otherwise.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Double.
     */
    Double getDouble(String key, Double defaultValue);

    
Get a float associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Float.
Returns:
The associated float./**
     * Get a float associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated float.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Float.
     */
    float getFloat(String key);

    
Get a float associated with the given configuration key. If the key doesn't map to
an existing object, the default value is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Float.
Returns:
The associated float./**
     * Get a float associated with the given configuration key. If the key doesn't map to
     * an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated float.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Float.
     */
    float getFloat(String key, float defaultValue);

    
Get a Float associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Float.
Returns:
The associated float if key is found and has valid format, default value
otherwise./**
     * Get a {@link Float} associated with the given configuration key. If the key doesn't
     * map to an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated float if key is found and has valid format, default value
     * otherwise.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Float.
     */
    Float getFloat(String key, Float defaultValue);

    
Get a int associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Integer.
Returns:
The associated int./**
     * Get a int associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated int.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Integer.
     */
    int getInt(String key);

    
Get a int associated with the given configuration key. If the key doesn't map to an
existing object, the default value is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Integer.
Returns:
The associated int./**
     * Get a int associated with the given configuration key. If the key doesn't map to an
     * existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated int.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Integer.
     */
    int getInt(String key, int defaultValue);

    
Get an Integer associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Integer.
Returns:
The associated int if key is found and has valid format, default value
otherwise./**
     * Get an {@link Integer} associated with the given configuration key. If the key
     * doesn't map to an existing object, the default value is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated int if key is found and has valid format, default value
     * otherwise.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Integer.
     */
    Integer getInteger(String key, Integer defaultValue);

    
Get a long associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the
key maps to an object that is not a Long.
Returns:
The associated long./**
     * Get a long associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated long.
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the
     * key maps to an object that is not a Long.
     */
    long getLong(String key);

    
Get a long associated with the given configuration key.
If the key doesn't map to an existing object, the default value
is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a Long.
Returns:
The associated long./**
     * Get a long associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated long.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a Long.
     */
    long getLong(String key, long defaultValue);

    
Get a Long associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a Long.
Returns:
The associated long if key is found and has valid
format, default value otherwise./**
     * Get a {@link Long} associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated long if key is found and has valid
     * format, default value otherwise.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a Long.
     */
    Long getLong(String key, Long defaultValue);

    
Get a short associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a Short.
Returns:
The associated short./**
     * Get a short associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated short.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a Short.
     */
    short getShort(String key);

    
Get a short associated with the given configuration key.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a Short.
Returns:
The associated short./**
     * Get a short associated with the given configuration key.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated short.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a Short.
     */
    short getShort(String key, short defaultValue);

    
Get a Short associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a Short.
Returns:
The associated short if key is found and has valid
        format, default value otherwise./**
     * Get a {@link Short} associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated short if key is found and has valid
     *         format, default value otherwise.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a Short.
     */
    Short getShort(String key, Short defaultValue);

    
Get a BigDecimal associated with the given configuration key. 
Params:
key – The configuration key.
Returns:
The associated BigDecimal if key is found and has valid format/**
     * Get a {@link BigDecimal} associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated BigDecimal if key is found and has valid format
     */
    BigDecimal getBigDecimal(String key);

    
Get a BigDecimal associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key –          The configuration key.
defaultValue – The default value.
Returns:
The associated BigDecimal if key is found and has valid
        format, default value otherwise./**
     * Get a {@link BigDecimal} associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key          The configuration key.
     * @param defaultValue The default value.
     *
     * @return The associated BigDecimal if key is found and has valid
     *         format, default value otherwise.
     */
    BigDecimal getBigDecimal(String key, BigDecimal defaultValue);

    
Get a BigInteger associated with the given configuration key. 
Params:
key – The configuration key.
Returns:
The associated BigInteger if key is found and has valid format/**
     * Get a {@link BigInteger} associated with the given configuration key.
     *
     * @param key The configuration key.
     *
     * @return The associated BigInteger if key is found and has valid format
     */
    BigInteger getBigInteger(String key);

    
Get a BigInteger associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned. 
Params:
key –          The configuration key.
defaultValue – The default value.
Returns:
The associated BigInteger if key is found and has valid
        format, default value otherwise./**
     * Get a {@link BigInteger} associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key          The configuration key.
     * @param defaultValue The default value.
     *
     * @return The associated BigInteger if key is found and has valid
     *         format, default value otherwise.
     */
    BigInteger getBigInteger(String key, BigInteger defaultValue);

    
Get a string associated with the given configuration key.
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the key maps to an object that
        is not a String.
Returns:
The associated string./**
     * Get a string associated with the given configuration key.
     *
     * @param key The configuration key.
     * @return The associated string.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *         is not a String.
     */
    String getString(String key);

    
Get a string associated with the given configuration key.
If the key doesn't map to an existing object, the default value
is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an object that
        is not a String.
Returns:
The associated string if key is found and has valid
        format, default value otherwise./**
     * Get a string associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated string if key is found and has valid
     *         format, default value otherwise.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *         is not a String.
     */
    String getString(String key, String defaultValue);

    
Get the value of a string property that is stored in encoded form in this configuration. This method obtains the value of the string property identified by the given key. This value is then passed to the provided ConfigurationDecoder. The value returned by the ConfigurationDecoder is passed to the caller. If the key is not associated with a value, the decoder is not invoked; depending on this configuration's settings either null is returned or an exception
is thrown.
Params:
key – the configuration key
decoder – the ConfigurationDecoder (must not be null)
Throws:
IllegalArgumentException – if a null decoder is passed
Returns:
the plain string value of the specified encoded property/**
     * Get the value of a string property that is stored in encoded form in this
     * configuration. This method obtains the value of the string property
     * identified by the given key. This value is then passed to the provided
     * {@code ConfigurationDecoder}. The value returned by the
     * {@code ConfigurationDecoder} is passed to the caller. If the key is not
     * associated with a value, the decoder is not invoked; depending on this
     * configuration's settings either <b>null</b> is returned or an exception
     * is thrown.
     *
     * @param key the configuration key
     * @param decoder the {@code ConfigurationDecoder} (must not be <b>null</b>)
     * @return the plain string value of the specified encoded property
     * @throws IllegalArgumentException if a <b>null</b> decoder is passed
     */
    String getEncodedString(String key, ConfigurationDecoder decoder);

    
Get the value of a string property that is stored in encoded form in this configuration using a default ConfigurationDecoder. This method works like the method with the same name, but it uses a default ConfigurationDecoder associated with this configuration. It depends on a specific implementation how this default decoder is obtained. 
Params:
key – the configuration key
Returns:
the plain string value of the specified encoded property/**
     * Get the value of a string property that is stored in encoded form in this
     * configuration using a default {@code ConfigurationDecoder}. This method
     * works like the method with the same name, but it uses a default
     * {@code ConfigurationDecoder} associated with this configuration. It
     * depends on a specific implementation how this default decoder is
     * obtained.
     *
     * @param key the configuration key
     * @return the plain string value of the specified encoded property
     */
    String getEncodedString(String key);

    
Get an array of strings associated with the given configuration key.
If the key doesn't map to an existing object an empty array is returned
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a String/List of Strings.
Returns:
The associated string array if key is found./**
     * Get an array of strings associated with the given configuration key.
     * If the key doesn't map to an existing object an empty array is returned
     *
     * @param key The configuration key.
     * @return The associated string array if key is found.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a String/List of Strings.
     */
    String[] getStringArray(String key);

    
Get a List of the values associated with the given configuration key. This method is different from the generic getList() method in that it does not recursively obtain all values stored for the specified property key. Rather, only the first level of the hierarchy is processed. So the resulting list may contain complex objects like arrays or collections - depending on the storage structure used by a concrete subclass. If the key doesn't map to an existing object, an empty List is returned. 
Params:
key – The configuration key.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a List.
Returns:
The associated List./**
     * Get a List of the values associated with the given configuration key.
     * This method is different from the generic {@code getList()} method in
     * that it does not recursively obtain all values stored for the specified
     * property key. Rather, only the first level of the hierarchy is processed.
     * So the resulting list may contain complex objects like arrays or
     * collections - depending on the storage structure used by a concrete
     * subclass. If the key doesn't map to an existing object, an empty List is
     * returned.
     *
     * @param key The configuration key.
     * @return The associated List.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a List.
     */
    List<Object> getList(String key);

    
Get a List of strings associated with the given configuration key.
If the key doesn't map to an existing object, the default value
is returned.
Params:
key – The configuration key.
defaultValue – The default value.
Throws:
ConversionException – is thrown if the key maps to an
        object that is not a List.
See Also:
getList(Class<Object>, String, List<Object>)
Returns:
The associated List of strings./**
     * Get a List of strings associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value
     * is returned.
     *
     * @param key The configuration key.
     * @param defaultValue The default value.
     * @return The associated List of strings.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an
     *         object that is not a List.
     * @see #getList(Class, String, List)
     */
    List<Object> getList(String key, List<?> defaultValue);

    
Get an object of the specified type associated with the given configuration key. If the key doesn't map to an existing object, the method returns null unless AbstractConfiguration.isThrowExceptionOnMissing() is set to true. 
Params:
cls – the target class of the value
key – the key of the value
Type parameters:
<T> – the target type of the value
Throws:
NoSuchElementException – if the key doesn't map to an existing object and throwExceptionOnMissing=true
ConversionException – if the value is not compatible with the
        requested type
Returns:
the value of the requested type for the key
Since:
2.0/**
     * Get an object of the specified type associated with the given
     * configuration key. If the key doesn't map to an existing object, the
     * method returns null unless
     * {@link AbstractConfiguration#isThrowExceptionOnMissing()} is set to
     * {@code true}.
     *
     * @param <T> the target type of the value
     * @param cls the target class of the value
     * @param key the key of the value
     * @return the value of the requested type for the key
     * @throws java.util.NoSuchElementException if the key doesn't map to an existing
     *         object and {@code throwExceptionOnMissing=true}
     * @throws org.apache.commons.configuration2.ex.ConversionException if the value is not compatible with the
     *         requested type
     * @since 2.0
     */
    <T> T get(Class<T> cls, String key);

    
Get an object of the specified type associated with the given
configuration key using a default value. If the key doesn't map to an
existing object, the default value is returned.
Params:
cls –          the target class of the value
key –          the key of the value
defaultValue – the default value
Type parameters:
<T> –          the target type of the value
Throws:
ConversionException – if the value is not
compatible with the requested type
Returns:
the value of the requested type for the key
Since:
2.0/**
     * Get an object of the specified type associated with the given
     * configuration key using a default value. If the key doesn't map to an
     * existing object, the default value is returned.
     *
     * @param <T>          the target type of the value
     * @param cls          the target class of the value
     * @param key          the key of the value
     * @param defaultValue the default value
     *
     * @return the value of the requested type for the key
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException if the value is not
     * compatible with the requested type
     *
     * @since 2.0
     */
    <T> T get(Class<T> cls, String key, T defaultValue);

    
Get an array of typed objects associated with the given configuration key.
If the key doesn't map to an existing object, an empty list is returned.
Params:
cls – the type expected for the elements of the array
key – The configuration key.
Throws:
ConversionException – is thrown if the key maps to an object that
    is not compatible with a list of the specified class.
Returns:
The associated array if the key is found, and the value compatible with the type specified.
Since:
2.0/**
     * Get an array of typed objects associated with the given configuration key.
     * If the key doesn't map to an existing object, an empty list is returned.
     *
     * @param cls the type expected for the elements of the array
     * @param key The configuration key.
     * @return The associated array if the key is found, and the value compatible with the type specified.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *     is not compatible with a list of the specified class.
     *
     * @since 2.0
     */
    Object getArray(Class<?> cls, String key);

    
Get an array of typed objects associated with the given configuration key.
If the key doesn't map to an existing object, the default value is returned.
Params:
cls –          the type expected for the elements of the array
key –          the configuration key.
defaultValue – the default value
Throws:
ConversionException – is thrown if the key maps to an object that
    is not compatible with an array of the specified class.
IllegalArgumentException – if the default value is not an array of the specified type
Returns:
The associated array if the key is found, and the value compatible with the type specified.
Since:
2.0
Deprecated:
This method should not be used any more because its signature does not allow type-safe invocations; use get(Class<Object>, String, Object) instead which offers the same functionality; for instance, to query for an array of ints use int[] result = config.get(int[].class, "myArrayKey", someDefault);./**
     * Get an array of typed objects associated with the given configuration key.
     * If the key doesn't map to an existing object, the default value is returned.
     *
     * @param cls          the type expected for the elements of the array
     * @param key          the configuration key.
     * @param defaultValue the default value
     * @return The associated array if the key is found, and the value compatible with the type specified.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *     is not compatible with an array of the specified class.
     * @throws IllegalArgumentException if the default value is not an array of the specified type
     *
     * @since 2.0
     * @deprecated This method should not be used any more because its signature
     * does not allow type-safe invocations; use {@link #get(Class, String, Object)}
     * instead which offers the same functionality; for instance, to query for an
     * array of ints use
     * {@code int[] result = config.get(int[].class, "myArrayKey", someDefault);}.
     */
    @Deprecated
    Object getArray(Class<?> cls, String key, Object defaultValue);

    
Get a list of typed objects associated with the given configuration key
returning an empty list if the key doesn't map to an existing object.
Params:
cls – the class expected for the elements of the list
key – The configuration key.
Type parameters:
<T> – the type expected for the elements of the list
Throws:
ConversionException – is thrown if the key maps to an object that
    is not compatible with a list of the specified class.
Returns:
The associated list if the key is found.
Since:
2.0/**
     * Get a list of typed objects associated with the given configuration key
     * returning an empty list if the key doesn't map to an existing object.
     *
     * @param <T> the type expected for the elements of the list
     * @param cls the class expected for the elements of the list
     * @param key The configuration key.
     * @return The associated list if the key is found.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *     is not compatible with a list of the specified class.
     *
     * @since 2.0
     */
    <T> List<T> getList(Class<T> cls, String key);

    
Get a list of typed objects associated with the given configuration key
returning the specified default value if the key doesn't map to an
existing object. This method recursively retrieves all values stored
for the passed in key, i.e. if one of these values is again a complex
object like an array or a collection (which may be the case for some
concrete subclasses), all values are extracted and added to the
resulting list - performing a type conversion if necessary.
Params:
cls –          the class expected for the elements of the list
key –          the configuration key.
defaultValue – the default value.
Type parameters:
<T> –          the type expected for the elements of the list
Throws:
ConversionException – is thrown if the key maps to an object that
    is not compatible with a list of the specified class.
Returns:
The associated List.
Since:
2.0/**
     * Get a list of typed objects associated with the given configuration key
     * returning the specified default value if the key doesn't map to an
     * existing object. This method recursively retrieves all values stored
     * for the passed in key, i.e. if one of these values is again a complex
     * object like an array or a collection (which may be the case for some
     * concrete subclasses), all values are extracted and added to the
     * resulting list - performing a type conversion if necessary.
     *
     * @param <T>          the type expected for the elements of the list
     * @param cls          the class expected for the elements of the list
     * @param key          the configuration key.
     * @param defaultValue the default value.
     * @return The associated List.
     *
     * @throws org.apache.commons.configuration2.ex.ConversionException is thrown if the key maps to an object that
     *     is not compatible with a list of the specified class.
     *
     * @since 2.0
     */
    <T> List<T> getList(Class<T> cls, String key, List<T> defaultValue);

    
Get a collection of typed objects associated with the given configuration key. This method works like getCollection(Class<Object>, String, Collection<Object>, Collection<Object>) passing in null as default value.
Params:
cls – the the element class of the result list
key – the configuration key
target – the target collection (may be null)
Type parameters:
<T> – the element type of the result list
Throws:
ConversionException – if the conversion is not possible
Returns:
the collection to which data was added
Since:
2.0/**
     * Get a collection of typed objects associated with the given configuration
     * key. This method works like
     * {@link #getCollection(Class, String, Collection, Collection)} passing in
     * <b>null</b> as default value.
     *
     * @param <T> the element type of the result list
     * @param cls the the element class of the result list
     * @param key the configuration key
     * @param target the target collection (may be <b>null</b>)
     * @return the collection to which data was added
     * @throws org.apache.commons.configuration2.ex.ConversionException if the conversion is not possible
     * @since 2.0
     */
    <T> Collection<T> getCollection(Class<T> cls, String key,
            Collection<T> target);

    
Get a collection of typed objects associated with the given configuration key using the values in the specified default collection if the key does not map to an existing object. This method is similar to getList(), however, it allows specifying a target collection. Results are added to this collection. This is useful if the data retrieved should be added to a specific kind of collection, e.g. a set to remove duplicates. The return value is as follows: 

If the key does not map to an existing object and the default value
is null, the method returns null.
If the target collection is not null and data has been added
(either from the resolved property value or from the default collection),
the target collection is returned.
If the target collection is null and data has been added
(either from the resolved property value or from the default collection),
return value is the target collection created by this method.

Params:
cls – the the element class of the result list
key – the configuration key
target – the target collection (may be null)
defaultValue – the default value (may be null)
Type parameters:
<T> – the element type of the result list
Throws:
ConversionException – if the conversion is not possible
Returns:
the collection to which data was added
Since:
2.0/**
     * Get a collection of typed objects associated with the given configuration
     * key using the values in the specified default collection if the key does
     * not map to an existing object. This method is similar to
     * {@code getList()}, however, it allows specifying a target collection.
     * Results are added to this collection. This is useful if the data
     * retrieved should be added to a specific kind of collection, e.g. a set to
     * remove duplicates. The return value is as follows:
     * <ul>
     * <li>If the key does not map to an existing object and the default value
     * is <b>null</b>, the method returns <b>null</b>.</li>
     * <li>If the target collection is not <b>null</b> and data has been added
     * (either from the resolved property value or from the default collection),
     * the target collection is returned.</li>
     * <li>If the target collection is <b>null</b> and data has been added
     * (either from the resolved property value or from the default collection),
     * return value is the target collection created by this method.</li>
     * </ul>
     *
     * @param <T> the element type of the result list
     * @param cls the the element class of the result list
     * @param key the configuration key
     * @param target the target collection (may be <b>null</b>)
     * @param defaultValue the default value (may be <b>null</b>)
     * @return the collection to which data was added
     * @throws org.apache.commons.configuration2.ex.ConversionException if the conversion is not possible
     * @since 2.0
     */
    <T> Collection<T> getCollection(Class<T> cls, String key,
            Collection<T> target, Collection<T> defaultValue);

    
Return a decorator immutable 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 immutable Configuration returned by subset("prefix") will contain the properties: 
   number = 1
   string = Apache
   = Jakarta
(The key for the value "Jakarta" is an empty string)
Params:
prefix – The prefix used to select the properties.
Returns:
a subset immutable configuration/**
     * Return a decorator immutable 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 immutable 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)
     *
     * @param prefix The prefix used to select the properties.
     * @return a subset immutable configuration
     */
    ImmutableConfiguration immutableSubset(String prefix);


}