Eclipse JDT
Release 3.0

org.eclipse.ltk.core.refactoring
Class Change

java.lang.Object
  extended byorg.eclipse.ltk.core.refactoring.Change
All Implemented Interfaces:
IAdaptable
Direct Known Subclasses:
CompositeChange, NullChange, TextChange, UndoTextFileChange

public abstract class Change
extends Object
implements IAdaptable

An abstract base implementation for object representing a generic change to the workbench. A Change object is typically created by calling Refactoring.createChange(). 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:

Below a code snippet that can be used to execute a change:
   Change change= createChange();
   try {
     change.initializeValidationState(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.initializeValidationState(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.

Clients may subclass this class.

Since:
3.0

Constructor Summary
protected Change()
          Constructs a new change object.
 
Method Summary
 void dispose()
          Disposes this change.
 Object getAdapter(Class adapter)
          
abstract  Object getModifiedElement()
          Returns the element modified by this Change.
abstract  String getName()
          Returns the human readable name of this change.
 Change getParent()
          Returns the parent change.
abstract  void initializeValidationData(IProgressMonitor pm)
          Hook method to initialize some internal state to provide an adequate answer for the isValid method.
 boolean isEnabled()
          Returns whether this change is enabled or not.
abstract  RefactoringStatus isValid(IProgressMonitor pm)
          Verifies that this change object is still valid and can be executed by calling perform.
abstract  Change perform(IProgressMonitor pm)
          Performs this change.
 void setEnabled(boolean enabled)
          Sets whether this change is enabled or not.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Change

protected Change()
Constructs a new change object.

Method Detail

getName

public abstract String getName()
Returns the human readable name of this change. The name MUST not be null.

Returns:
the human readable name of this change

isEnabled

public boolean isEnabled()
Returns whether this change is enabled or not. Disabled changes must not be executed.

Returns:
true if the change is enabled; false otherwise.

setEnabled

public void setEnabled(boolean enabled)
Sets whether this change is enabled or not.

Parameters:
enabled - true to enable this change; false otherwise

getParent

public Change getParent()
Returns the parent change. Returns null if no parent exists.

Returns:
the parent change

initializeValidationData

public abstract void initializeValidationData(IProgressMonitor pm)
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:

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.

Parameters:
pm - a progress monitor

isValid

public abstract RefactoringStatus isValid(IProgressMonitor pm)
                                   throws CoreException,
                                          OperationCanceledException
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.

Parameters:
pm - a progress monitor.
Returns:
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
OperationCanceledException - if the validation check got cancelled

perform

public abstract Change perform(IProgressMonitor pm)
                        throws CoreException
Performs this change. If this method is call 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.

Parameters:
pm - a progress monitor
Returns:
the undo change for this change object or null if no undo is provided
Throws:
CoreException - if an error occurred during change execution

dispose

public void dispose()
Disposes this change. Subclasses that override this method typically unregister listeners which got registered during the call to initializeValidationState.

Subclasses may override this method.


getModifiedElement

public abstract Object getModifiedElement()
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

getAdapter

public Object getAdapter(Class adapter)

Specified by:
getAdapter in interface IAdaptable

Eclipse JDT
Release 3.0

Copyright (c) IBM Corp. and others 2000, 2004. All Rights Reserved.