http://www.eclipse.org/platform: Refactoring Core (Eclipse Foundation) 
Copyright (c) 2000, 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) 2000, 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.ltk.core.refactoring;

import org.eclipse.core.runtime.Assert;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IAdaptable;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.OperationCanceledException;
import org.eclipse.core.runtime.Platform;


An abstract base implementation for object representing a generic change
to the workbench. A Change object is typically created by calling Refactoring.createChange(IProgressMonitor). This class should be subclassed by clients wishing to provide new changes. 
 Changes are best executed by using a PerformChangeOperation. If clients execute a change directly then the following life cycle has to be honored:


    
  
  • After a single change or a tree of changes has been created, the
      method initializeValidationData has to be called.
    • 
  
  • The method isValid can be used to determine if a change can still be applied to the workspace. If the method returns a RefactoringStatus with a severity of FATAL then the change has to be treated as invalid. Performing an invalid change isn't allowed and results in an unspecified result. This method can be called multiple times. 
  • Then the method perform can be called. A disabled change
      must not be executed. The perform method can only be called
      once. After a change has been executed, only the method dispose
      must be called.
    • 
  
  • the method dispose has to be called either after the
      perform method
      has been called or if a change is no longer needed. The second case
      for example occurs when the undo stack gets flushed and all change
      objects managed by the undo stack are no longer needed. The method
      dispose is typically implemented to unregister listeners
      registered during the
      method initializeValidationData. There is no guarantee
      that initializeValidationData, isValid,
      or perform has been called before dispose
      is called.


Here is a code snippet that can be used to execute a change:

  Change change= createChange();
  try {
    change.initializeValidationData(pm);
    ....
    if (!change.isEnabled())
        return;
    RefactoringStatus valid= change.isValid(new SubProgressMonitor(pm, 1));
    if (valid.hasFatalError())
        return;
    Change undo= change.perform(new SubProgressMonitor(pm, 1));
    if (undo != null) {
       undo.initializeValidationData(new SubProgressMonitor(pm, 1));
       // do something with the undo object
    }
  } finally {
    change.dispose();
  }




It is important that implementors of this abstract class provide an adequate
implementation of isValid and that they provide an undo change
via the return value of the method perform. If no undo can be
provided then the perform method is allowed to return null. But
implementors should be aware that not providing an undo object for a change
object that is part of a larger change tree will result in the fact that for
the whole change tree no undo object will be present.




Changes which are returned as top-level changes (e.g. by Refactoring.createChange())
can optionally return a descriptor object of the refactoring which created this change object.




Clients may subclass this class.



Since:3.0
/**
 * An abstract base implementation for object representing a generic change
 * to the workbench. A <code>Change</code> object is typically created by
 * calling {@link Refactoring#createChange(IProgressMonitor)}. This class should be
 * subclassed by clients wishing to provide new changes.
 * <p>
 * Changes are best executed by using a {@link PerformChangeOperation}. If clients
 * execute a change directly then the following life cycle has to be honored:</p>
 * <ul>
 *   <li>After a single change or a tree of changes has been created, the
 *       method <code>initializeValidationData</code> has to be called.</li>
 *   <li>The method <code>isValid</code> can be used to determine if a change
 *       can still be applied to the workspace. If the method returns a {@link
 *       RefactoringStatus} with a severity of FATAL then the change has to be
 *       treated as invalid. Performing an invalid change isn't allowed and
 *       results in an unspecified result. This method can be called multiple
 *       times.
 *   <li>Then the method <code>perform</code> can be called. A disabled change
 *       must not be executed. The <code>perform</code> method can only be called
 *       once. After a change has been executed, only the method <code>dispose</code>
 *       must be called.</li>
 *   <li>the method <code>dispose</code> has to be called either after the
 *       <code>perform</code> method
 *       has been called or if a change is no longer needed. The second case
 *       for example occurs when the undo stack gets flushed and all change
 *       objects managed by the undo stack are no longer needed. The method
 *       <code>dispose</code> is typically implemented to unregister listeners
 *       registered during the
 *       method <code>initializeValidationData</code>. There is no guarantee
 *       that <code>initializeValidationData</code>, <code>isValid</code>,
 *       or <code>perform</code> has been called before <code>dispose</code>
 *       is called.
 * </ul>
 * Here is a code snippet that can be used to execute a change:
 * <pre>
 *   Change change= createChange();
 *   try {
 *     change.initializeValidationData(pm);
 * 
 *     ....
 *
 *     if (!change.isEnabled())
 *         return;
 *     RefactoringStatus valid= change.isValid(new SubProgressMonitor(pm, 1));
 *     if (valid.hasFatalError())
 *         return;
 *     Change undo= change.perform(new SubProgressMonitor(pm, 1));
 *     if (undo != null) {
 *        undo.initializeValidationData(new SubProgressMonitor(pm, 1));
 *        // do something with the undo object
 *     }
 *   } finally {
 *     change.dispose();
 *   }
 * </pre>
 * <p>
 * It is important that implementors of this abstract class provide an adequate
 * implementation of <code>isValid</code> and that they provide an undo change
 * via the return value of the method <code>perform</code>. If no undo can be
 * provided then the <code>perform</code> method is allowed to return <code>null</code>. But
 * implementors should be aware that not providing an undo object for a change
 * object that is part of a larger change tree will result in the fact that for
 * the whole change tree no undo object will be present.
 * </p>
 * <p>
 * Changes which are returned as top-level changes (e.g. by <code>Refactoring.createChange()</code>)
 * can optionally return a descriptor object of the refactoring which created this change object.
 * </p>
 * <p>
 * Clients may subclass this class.
 * </p>
 * 
 * @since 3.0
 */
public abstract class Change implements IAdaptable {

	private Change fParent;
	private boolean fIsEnabled= true;

	
Constructs a new change object.

/**
	 * Constructs a new change object.
	 */
	protected Change() {
	}

	
Returns a descriptor of this change.

 Subclasses of changes created by Refactoring.createChange(IProgressMonitor) should override this method to return a RefactoringChangeDescriptor. A change tree created by a particular refactoring is supposed to contain at most one change which returns a refactoring descriptor. Refactorings usually return an instance of CompositeChange in their Refactoring.createChange(IProgressMonitor) method which implements this method. The refactoring framework searches the change tree top-down until a refactoring descriptor is found. 


Returns:a descriptor of this change, or null if this
        change does not provide a change descriptor.
Since:3.2
/**
	 * Returns a descriptor of this change.
	 * <p>
	 * Subclasses of changes created by
	 * {@link Refactoring#createChange(IProgressMonitor)} should override this
	 * method to return a {@link RefactoringChangeDescriptor}. A change tree
	 * created by a particular refactoring is supposed to contain at most one
	 * change which returns a refactoring descriptor. Refactorings usually
	 * return an instance of {@link CompositeChange} in their
	 * {@link Refactoring#createChange(IProgressMonitor)} method which
	 * implements this method. The refactoring framework searches the change
	 * tree top-down until a refactoring descriptor is found.
	 * </p>
	 *
	 * @return a descriptor of this change, or <code>null</code> if this
	 *         change does not provide a change descriptor.
	 *
	 * @since 3.2
	 */
	public ChangeDescriptor getDescriptor() {
		return null;
	}

	
Returns the human readable name of this change. The
name MUST not be null.

Returns:the human readable name of this change
/**
	 * Returns the human readable name of this change. The
	 * name <em>MUST</em> not be <code>null</code>.
	 *
	 * @return the human readable name of this change
	 */
	public abstract String getName();

	
Returns whether this change is enabled or not. Disabled changes
must not be executed.

Returns:true if the change is enabled; false
 otherwise.
/**
	 * Returns whether this change is enabled or not. Disabled changes
	 * must not be executed.
	 *
	 * @return <code>true</code> if the change is enabled; <code>false</code>
	 *  otherwise.
	 */
	public boolean isEnabled() {
		return fIsEnabled;
	}

	
Sets whether this change is enabled or not.

Params:
  • enabled – true to enable this change; 
 false otherwise
/**
	 * Sets whether this change is enabled or not.
	 *
	 * @param enabled <code>true</code> to enable this change; <code>
	 *  false</code> otherwise
	 */
	public void setEnabled(boolean enabled) {
		fIsEnabled= enabled;
	}

	
Sets the enablement state of this change in a shallow way.
For changes having children this means that only this change's
enablement state changes. The children are left untouched.

Params:
  • enabled – true to enable this change; 
 false otherwise
Since:3.1
/**
	 * Sets the enablement state of this change in a shallow way.
	 * For changes having children this means that only this change's
	 * enablement state changes. The children are left untouched.
	 *
	 * @param enabled <code>true</code> to enable this change; <code>
	 *  false</code> otherwise
	 *
	 * @since 3.1
	 */
	public final void setEnabledShallow(boolean enabled) {
		fIsEnabled= enabled;
	}

	
Returns the parent change. Returns null if no
parent exists.

Returns:the parent change
/**
	 * Returns the parent change. Returns <code>null</code> if no
	 * parent exists.
	 *
	 * @return the parent change
	 */
	public Change getParent() {
		return fParent;
	}

	
Sets the parent of this change. Requires that this change isn't already
connected to a parent. The parent can be null to disconnect
this change from a parent.

Params:
  • parent – the parent of this change or null
/**
	 * Sets the parent of this change. Requires that this change isn't already
	 * connected to a parent. The parent can be <code>null</code> to disconnect
	 * this change from a parent.
	 *
	 * @param parent the parent of this change or <code>null</code>
	 */
	/* package */ void setParent(Change parent) {
		if (parent != null)
			Assert.isTrue(fParent == null);
		fParent= parent;
	}

	
Hook method to initialize some internal state to provide an adequate answer
for the isValid method. This method gets called after a change
or a whole change tree has been created.


Typically this method is implemented in one of the following ways:

    
  
  • the change hooks up a listener on some delta notification mechanism
      and marks itself as invalid if it receives a certain delta. Is this
      the case the implementor must take care of unhooking the listener
      in dispose.
    • 
  
  • the change remembers some information allowing to decide if a change
      object is still valid when isValid is called.
    • 




For example, a change object that manipulates the content of an IFile
could either listen to resource changes and detect that the file got changed or
it could remember some content stamp and compare it with the actual content stamp
when isValid is called.



Params:
  • pm – a progress monitor
/**
	 * Hook method to initialize some internal state to provide an adequate answer
	 * for the <code>isValid</code> method. This method gets called after a change
	 * or a whole change tree has been created.
	 * <p>
	 * Typically this method is implemented in one of the following ways:
	 * <ul>
	 *   <li>the change hooks up a listener on some delta notification mechanism
	 *       and marks itself as invalid if it receives a certain delta. Is this
	 *       the case the implementor must take care of unhooking the listener
	 *       in <code>dispose</code>.</li>
	 *   <li>the change remembers some information allowing to decide if a change
	 *       object is still valid when <code>isValid</code> is called.</li>
	 * </ul>
	 * <p>
	 * For example, a change object that manipulates the content of an <code>IFile</code>
	 * could either listen to resource changes and detect that the file got changed or
	 * it could remember some content stamp and compare it with the actual content stamp
	 * when <code>isValid</code> is called.
	 * </p>
	 *
	 * @param pm a progress monitor
	 */
	public abstract void initializeValidationData(IProgressMonitor pm);

	
Verifies that this change object is still valid and can be executed by calling
perform. If a refactoring status with a severity of RefactoringStatus.FATAL is returned then the change has to be treated as invalid and can no longer be executed. Performing such a change produces an unspecified result and will very likely throw an exception. 
 This method is also called by the UndoManager to decide if an undo or redo change is still valid and therefore can be executed. 


Params:
  • pm – a progress monitor.
Throws:
Returns:a refactoring status describing the outcome of the validation check
/**
	 * Verifies that this change object is still valid and can be executed by calling
	 * <code>perform</code>. If a refactoring status  with a severity of {@link
	 * RefactoringStatus#FATAL} is returned then the change has to be treated as invalid
	 * and can no longer be executed. Performing such a change produces an unspecified
	 * result and will very likely throw an exception.
	 * <p>
	 * This method is also called by the {@link IUndoManager UndoManager} to decide if
	 * an undo or redo change is still valid and therefore can be executed.
	 * </p>
	 *
	 * @param pm a progress monitor.
	 *
	 * @return a refactoring status describing the outcome of the validation check
	 *
	 * @throws CoreException if an error occurred during validation check. The change
	 *  is to be treated as invalid if an exception occurs
	 *
	 * @throws OperationCanceledException if the validation check got canceled
	 */
	public abstract RefactoringStatus isValid(IProgressMonitor pm) throws CoreException, OperationCanceledException;

	
Performs this change. If this method is called on an invalid or disabled change object the result is unspecified. Changes should in general not respond to IProgressMonitor.isCanceled() since canceling a change tree in the middle of its execution leaves the workspace in a half changed state. 
Params:
  • pm – a progress monitor
Throws:
Returns:the undo change for this change object or null if no
 undo is provided
/**
	 * Performs this change. If this method is called on an invalid or disabled change
	 * object the result is unspecified. Changes should in general not respond to
	 * {@link IProgressMonitor#isCanceled()} since canceling a change tree in the
	 * middle of its execution leaves the workspace in a half changed state.
	 *
	 * @param pm a progress monitor
	 *
	 * @return the undo change for this change object or <code>null</code> if no
	 *  undo is provided
	 *
	 * @throws CoreException if an error occurred during change execution
	 */
	public abstract Change perform(IProgressMonitor pm) throws CoreException;

	
Disposes this change. Subclasses that override this method typically unregister listeners
which got registered during the call to 
initializeValidationData.


Subclasses may override this method.



/**
	 * Disposes this change. Subclasses that override this method typically unregister listeners
	 * which got registered during the call to <code>
	 * initializeValidationData</code>.
	 * <p>
	 * Subclasses may override this method.
	 * </p>
	 */
	public void dispose() {
		// empty default implementation
	}

	
Returns the element modified by this Change. The method may return
null if the change isn't related to an element.

Returns:the element modified by this change
/**
	 * Returns the element modified by this <code>Change</code>. The method may return
	 * <code>null</code> if the change isn't related to an element.
	 *
	 * @return the element modified by this change
	 */
	public abstract Object getModifiedElement();

	
Returns the elements affected by this change or null if
the affected elements cannot be determined. Returns an empty array
if the change doesn't modify any elements.


This default implementation returns null to indicate that
the affected elements are unknown. Subclasses should reimplement this method
if they can compute the set of affected elements.



Returns:the elements affected by this change or null if
 the affected elements cannot be determined
Since:3.1
/**
	 * Returns the elements affected by this change or <code>null</code> if
	 * the affected elements cannot be determined. Returns an empty array
	 * if the change doesn't modify any elements.
	 * <p>
	 * This default implementation returns <code>null</code> to indicate that
	 * the affected elements are unknown. Subclasses should reimplement this method
	 * if they can compute the set of affected elements.
	 * </p>
	 *
	 * @return the elements affected by this change or <code>null</code> if
	 *  the affected elements cannot be determined
     *
     * @since 3.1
	 */
	public Object[] getAffectedObjects() {
		return null;
	}

	@Override
	public <T> T getAdapter(Class<T> adapter) {
		T result= Platform.getAdapterManager().getAdapter(this, adapter);
		if (result != null)
			return result;
		if (fParent != null)
			return fParent.getAdapter(adapter);
		return null;
	}
}