Class Change

All Implemented Interfaces:
Direct Known Subclasses:
CompositeChange, NullChange, ResourceChange, TextEditBasedChange, 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(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 {


     if (!change.isEnabled())
     RefactoringStatus valid= change.isValid(subMonitor.newChild(1));
     if (valid.hasFatalError())
     Change undo= change.perform(subMonitor.newChild(1));
     if (undo != null) {
        // do something with the undo object
   } finally {

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.

  • Constructor Details

    • Change

      protected Change()
      Constructs a new change object.
  • Method Details

    • getDescriptor

      public ChangeDescriptor getDescriptor()
      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.

      a descriptor of this change, or null if this change does not provide a change descriptor.
    • getName

      public abstract String getName()
      Returns the human readable name of this change. The name MUST not be null.
      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.
      true if the change is enabled; false otherwise.
    • setEnabled

      public void setEnabled(boolean enabled)
      Sets whether this change is enabled or not.
      enabled - true to enable this change; false otherwise
    • setEnabledShallow

      public final void setEnabledShallow(boolean 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.
      enabled - true to enable this change; false otherwise
    • getParent

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

      • 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.

      pm - a progress monitor
    • isValid

      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.

      pm - a progress monitor.
      a refactoring status describing the outcome of the validation check
      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 canceled
    • perform

      public abstract Change perform(IProgressMonitor pm) throws CoreException
      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.
      pm - a progress monitor
      the undo change for this change object or null if no undo is provided
      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 initializeValidationData.

      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.
      the element modified by this change
    • getAffectedObjects

      public Object[] getAffectedObjects()
      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.

      the elements affected by this change or null if the affected elements cannot be determined
    • getAdapter

      public <T> T getAdapter(Class<T> adapter)
      Description copied from interface: IAdaptable
      Returns an object which is an instance of the given class associated with this object. Returns null if no such object can be found.

      Clients may implement this method but should generally call Adapters.adapt(Object, Class, boolean) rather than invoking it directly.

      Specified by:
      getAdapter in interface IAdaptable
      Type Parameters:
      T - the class type
      adapter - the adapter class to look up
      a object of the given class, or null if this object does not have an adapter for the given class