developers/org.eclipse.ease.helpgenerator/src/org/eclipse/ease/helpgenerator/IMemento.java

/*******************************************************************************
 * Copyright (c) 2000, 2012 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.ease.helpgenerator;

import org.w3c.dom.DOMException;

/**
 * Interface to a memento used for saving the important state of an object in a form that can be persisted in the file system.
 * <p>
 * Mementos were designed with the following requirements in mind:
 * <ol>
 * <li>Certain objects need to be saved and restored across platform sessions.</li>
 * <li>When an object is restored, an appropriate class for an object might not be available. It must be possible to skip an object in this case.</li>
 * <li>When an object is restored, the appropriate class for the object may be different from the one when the object was originally saved. If so, the new class
 * should still be able to read the old form of the data.</li>
 * </ol>
 * </p>
 * <p>
 * Mementos meet these requirements by providing support for storing a mapping of arbitrary string keys to primitive values, and by allowing mementos to have
 * other mementos as children (arranged into a tree). A robust external storage format based on XML is used.
 * </p>
 * <p>
 * The key for an attribute may be any alpha numeric value that doesn't start with a number. eg: [A-Za-z][A-Za-z0-9]* Using '.' is unsupported. However, the
 * value of <code>TAG_ID</code> is reserved for internal use.
 * </p>
 * <p>
 * The default implementation can throw a {@link DOMException} for createChild and put operations. See {@link XMLMemento}.
 * </p>
 * <p>
 * This interface is not intended to be implemented or extended by clients.
 * </p>
 * 
 * @see IPersistableElement
 * @see IElementFactory
 * @see XMLMemento
 * @noimplement This interface is not intended to be implemented by clients.
 */
public interface IMemento {
	/**
	 * Special reserved key used to store the memento id (value <code>"IMemento.internal.id"</code>).
	 * 
	 * @see #getID()
	 */
	public static final String TAG_ID = "IMemento.internal.id"; //$NON-NLS-1$

	/**
	 * Creates a new child of this memento with the given type.
	 * <p>
	 * The <code>getChild</code> and <code>getChildren</code> methods are used to retrieve children of a given type.
	 * </p>
	 * 
	 * @param type
	 *            the type
	 * @return a new child memento
	 * @see #getChild
	 * @see #getChildren
	 */
	public IMemento createChild(String type);

	/**
	 * Creates a new child of this memento with the given type and id. The id is stored in the child memento (using a special reserved key, <code>TAG_ID</code>)
	 * and can be retrieved using <code>getId</code>.
	 * <p>
	 * The <code>getChild</code> and <code>getChildren</code> methods are used to retrieve children of a given type.
	 * </p>
	 * 
	 * @param type
	 *            the type
	 * @param id
	 *            the child id
	 * @return a new child memento with the given type and id
	 * @see #getID
	 */
	public IMemento createChild(String type, String id);

	/**
	 * Returns the first child with the given type id.
	 * 
	 * @param type
	 *            the type id
	 * @return the first child with the given type. May return <code>null</code> .
	 */
	public IMemento getChild(String type);

	/**
	 * Returns all children of this node.
	 * 
	 * @return an array of children of this node. This will not be <code>null</code>. If there are no children, an array of length zero will be returned.
	 * @since 3.8
	 */
	public IMemento[] getChildren();

	/**
	 * Returns all children with the given type id.
	 * 
	 * @param type
	 *            the type id
	 * @return an array of children with the given type. This will not be <code>null</code>. If there are no keys, an array of length zero will be returned.
	 */
	public IMemento[] getChildren(String type);

	/**
	 * Returns the floating point value of the given key.
	 * 
	 * @param key
	 *            the key
	 * @return the value, or <code>null</code> if the key was not found or was found but was not a floating point number
	 */
	public Float getFloat(String key);

	/**
	 * Returns the type for this memento.
	 * 
	 * @return the memento type
	 * @see #createChild(java.lang.String)
	 * @see #createChild(java.lang.String,java.lang.String)
	 * @since 3.4
	 */
	public String getType();

	/**
	 * Returns the id for this memento.
	 * 
	 * @return the memento id, or <code>null</code> if none
	 * @see #createChild(java.lang.String,java.lang.String)
	 */
	public String getID();

	/**
	 * Returns the integer value of the given key.
	 * 
	 * @param key
	 *            the key
	 * @return the value, or <code>null</code> if the key was not found or was found but was not an integer
	 */
	public Integer getInteger(String key);

	/**
	 * Returns the string value of the given key.
	 * 
	 * @param key
	 *            the key
	 * @return the value, or <code>null</code> if the key was not found
	 */
	public String getString(String key);

	/**
	 * Returns the boolean value of the given key.
	 * 
	 * @param key
	 *            the key
	 * @return the value, or <code>null</code> if the key was not found
	 * @since 3.4
	 */
	public Boolean getBoolean(String key);

	/**
	 * Returns the data of the Text node of the memento. Each memento is allowed only one Text node.
	 * 
	 * @return the data of the Text node of the memento, or <code>null</code> if the memento has no Text node.
	 * @since 2.0
	 */
	public String getTextData();

	/**
	 * Returns an array of all the attribute keys of the memento. This will not be <code>null</code>. If there are no keys, an array of length zero will be
	 * returned.
	 * 
	 * @return an array with all the attribute keys of the memento
	 * @since 3.4
	 */
	public String[] getAttributeKeys();

	/**
	 * Sets the value of the given key to the given floating point number.
	 * 
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 */
	public void putFloat(String key, float value);

	/**
	 * Sets the value of the given key to the given integer.
	 * 
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 */
	public void putInteger(String key, int value);

	/**
	 * Copy the attributes and children from <code>memento</code> to the receiver.
	 * 
	 * @param memento
	 *            the IMemento to be copied.
	 */
	public void putMemento(IMemento memento);

	/**
	 * Sets the value of the given key to the given string.
	 * 
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 */
	public void putString(String key, String value);

	/**
	 * Sets the value of the given key to the given boolean value.
	 * 
	 * @param key
	 *            the key
	 * @param value
	 *            the value
	 * @since 3.4
	 */
	public void putBoolean(String key, boolean value);

	/**
	 * Sets the memento's Text node to contain the given data. Creates the Text node if none exists. If a Text node does exist, it's current contents are
	 * replaced. Each memento is allowed only one text node.
	 * 
	 * @param data
	 *            the data to be placed on the Text node
	 * @since 2.0
	 */
	public void putTextData(String data);
}