http://www.eclipse.org/platform: Commands (Eclipse Foundation) 
Copyright (c) 2005, 2015 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation

/*******************************************************************************
 * Copyright (c) 2005, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.commands.operations;



This class is used to maintain the instance of the operation history that
should be used by classes that access the undo or redo history and add
undoable operations to the history.


It is intended that an application can create an operation history appropriate
for its needs and set it into this class.  Otherwise, a default operation history
will be created.  The operation history may only be set one time.  All classes that
access an operations history use this class to obtain the correct instance.

Since:3.1
/**
 * <p>
 * This class is used to maintain the instance of the operation history that
 * should be used by classes that access the undo or redo history and add
 * undoable operations to the history.
 *
 * <p>
 * It is intended that an application can create an operation history appropriate
 * for its needs and set it into this class.  Otherwise, a default operation history
 * will be created.  The operation history may only be set one time.  All classes that
 * access an operations history use this class to obtain the correct instance.
 *
 * @since 3.1
 */
public final class OperationHistoryFactory {

	private static IOperationHistory operationHistory;

	
Return the operation history to be used for managing undoable operations.

Returns:the operation history to be used for executing, undoing, and
        redoing operations.
/**
	 * Return the operation history to be used for managing undoable operations.
	 *
	 * @return the operation history to be used for executing, undoing, and
	 *         redoing operations.
	 */
	public static IOperationHistory getOperationHistory() {
		if (operationHistory == null) {
			operationHistory = new DefaultOperationHistory();
		}
		return operationHistory;
	}

	
Set the operation history to be used for managing undoable operations.
This method may only be called one time, and must be called before any
request to get the history.  Attempts to set the operation history will
be ignored after it has been already set, or after a default one has
been created.

Params:
  • history – 
           the operation history to be used for executing, undoing, and
           redoing operations.
/**
	 * Set the operation history to be used for managing undoable operations.
	 * This method may only be called one time, and must be called before any
	 * request to get the history.  Attempts to set the operation history will
	 * be ignored after it has been already set, or after a default one has
	 * been created.
	 *
	 * @param history
	 *            the operation history to be used for executing, undoing, and
	 *            redoing operations.
	 */
	public static void setOperationHistory(IOperationHistory history) {
		// If one has already been set or created, ignore this request.
		if (operationHistory == null) {
			operationHistory = history;
		}
	}

	private OperationHistoryFactory() {
		// may not be instantiated
	}

}