java.lang.Object
- org.openrefine.history.History

```
public class History
extends Object
```
Track done and undone changes. Done changes can be undone; undone changes can be redone. Each change is actually not tracked directly but through a history entry. The history entry stores only the metadata, while the change object stores the actual data. Thus, the history entries are much smaller and can be kept in memory, while the change objects are only loaded into memory on demand.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

protected static class History.Step
A step in the history, which is a Grid with associated metadata.

Field Summary

Fields
Modifier and Type	Field	Description
`protected int`	`_cachedPosition`
`protected ExecutorService`	`_cachingExecutorService`
`protected Future<Void>`	`_cachingFuture`
`protected ChangeDataStore`	`_dataStore`
`protected int`	`_desiredCachedPosition`
`protected List<HistoryEntry>`	`_entries`
`protected GridCache`	`_gridStore`
`protected Instant`	`_lastModified`
`protected int`	`_position`
`protected int`	`_positionBeingCached`
`protected long`	`_projectId`
`protected List<History.Step>`	`_steps`

Constructor Summary

Constructors
Constructor	Description
`History(Grid initialGrid, ChangeDataStore dataStore, GridCache gridStore, long projectId)`	Creates an empty on an initial grid.
`History(Grid initialGrid, ChangeDataStore dataStore, GridCache gridStore, List<HistoryEntry> entries, int position, long projectId)`	Constructs a history with an initial grid and a list of history entries.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`OperationApplicationResult`	`addEntry(long id, Operation operation)`	Adds a `HistoryEntry` to the list of past histories.
`OperationApplicationResult`	`addEntry(Operation operation)`	Applies an operation on top of the existing history.
`protected void`	`cacheGridOnDisk(int position)`
`boolean`	`currentGridNeedsRefreshing()`	Is the current grid incomplete?
`void`	`dispose()`	Uncaches all grids from memory and stops all related fetching and caching processes.
`int`	`entryIndex(long entryID)`	Return the position of the history entry with the supplied id, or throws `IllegalArgumentException` if that id cannot be found.
`int`	`getCachedPosition()`
`ChangeDataStore`	`getChangeDataStore()`
`long`	`getCurrentEntryId()`
`Grid`	`getCurrentGrid()`	Returns the state of the grid at the current position in the history.
`List<HistoryEntry>`	`getEntries()`
`protected HistoryEntry`	`getEntry(long entryID)`
`protected Grid`	`getGrid(int position, boolean refresh)`	Returns the state of the grid at a given index in the history
`GridCache`	`getGridCache()`
`Grid`	`getInitialGrid()`	Returns the state of the grid at before any operation was applied on it
`Instant`	`getLastModified()`	The last time this history was modified (or created).
`List<HistoryEntry>`	`getLastPastEntries(int count)`
`int`	`getPosition()`
`long`	`getPrecedingEntryID(long entryID)`	Given an history entry id, return the id of the preceding history entry, or -1 if there is none.
`void`	`refreshCurrentGrid()`
`protected void`	`uncacheGridFromDisk(int position)`
`GridPreservation`	`undoRedo(long lastDoneEntryID)`	Rewinds or brings the history forward.
`protected void`	`updateCachedPosition()`
`void`	`waitForCaching()`	Wait for any caching operation currently being executed asynchronously.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - _projectId
```
protected final long _projectId
```
  - _entries
```
protected List<HistoryEntry> _entries
```
  - _position
```
protected int _position
```
  - _cachedPosition
```
protected int _cachedPosition
```
  - _desiredCachedPosition
```
protected int _desiredCachedPosition
```
  - _positionBeingCached
```
protected int _positionBeingCached
```
  - _cachingFuture
```
protected Future<Void> _cachingFuture
```
  - _cachingExecutorService
```
protected final ExecutorService _cachingExecutorService
```
  - _steps
```
protected List<History.Step> _steps
```
  - _dataStore
```
protected ChangeDataStore _dataStore
```
  - _gridStore
```
protected GridCache _gridStore
```
  - _lastModified
```
protected Instant _lastModified
```
- Constructor Detail
  - History
```
public History(Grid initialGrid,
               ChangeDataStore dataStore,
               GridCache gridStore,
               long projectId)
```
    Creates an empty on an initial grid.
    
    Parameters:
    
    initialGrid - the initial state of the project
    
    dataStore - where to store change data
    
    gridStore - where to store intermediate cached grids
  - History
```
public History(Grid initialGrid,
               ChangeDataStore dataStore,
               GridCache gridStore,
               List<HistoryEntry> entries,
               int position,
               long projectId)
        throws OperationException
```
    Constructs a history with an initial grid and a list of history entries.
    
    Parameters:
    
    initialGrid - the first grid of the project, at creation time
    
    dataStore - where change data is stored for all changes of the project
    
    entries - the list of entries of the history
    
    position - the current position in the history
    
    Throws:
    
    OperationException - if one step in the list of history entries failed to apply to the supplied grid
- Method Detail
  - waitForCaching
```
public void waitForCaching()
                    throws InterruptedException,
                           ExecutionException
```
    Wait for any caching operation currently being executed asynchronously. Mostly for testing purposes.
    
    Throws:
    
    ExecutionException
    
    InterruptedException
  - getCurrentGrid
```
public Grid getCurrentGrid()
```
    Returns the state of the grid at the current position in the history.
  - currentGridNeedsRefreshing
```
public boolean currentGridNeedsRefreshing()
```
    Is the current grid incomplete? If so, it should be refreshed with refreshCurrentGrid() after a while.
  - getInitialGrid
```
public Grid getInitialGrid()
```
    Returns the state of the grid at before any operation was applied on it
  - getGrid
```
protected Grid getGrid(int position,
                       boolean refresh)
                throws OperationException
```
    Returns the state of the grid at a given index in the history
    
    Parameters:
    
    position - a 0-based index in the list of successive grids
    
    refresh - whether the grid should be refreshed if it depends on change data being currently fetched
    
    Throws:
    
    OperationException
  - getPosition
```
public int getPosition()
```
  - getCurrentEntryId
```
public long getCurrentEntryId()
```
  - getCachedPosition
```
public int getCachedPosition()
```
  - getEntries
```
public List<HistoryEntry> getEntries()
```
  - getChangeDataStore
```
public ChangeDataStore getChangeDataStore()
```
  - getGridCache
```
public GridCache getGridCache()
```
  - getLastModified
```
public Instant getLastModified()
```
    The last time this history was modified (or created).
  - addEntry
```
public OperationApplicationResult addEntry(Operation operation)
```
    Applies an operation on top of the existing history. This will modify this instance. If the operation application failed, the exception will be returned in OperationApplicationResult.getException().
    
    Parameters:
    
    operation - the operation to apply.
  - addEntry
```
public OperationApplicationResult addEntry(long id,
                                           Operation operation)
```
    Adds a HistoryEntry to the list of past histories. Adding a new entry clears all currently held future histories
  - cacheGridOnDisk
```
protected void cacheGridOnDisk(int position)
                        throws OperationException,
                               IOException
```
    Throws:
    
    OperationException
    
    IOException
  - uncacheGridFromDisk
```
protected void uncacheGridFromDisk(int position)
                            throws IOException,
                                   OperationException
```
    Throws:
    
    IOException
    
    OperationException
  - updateCachedPosition
```
protected void updateCachedPosition()
```
  - refreshCurrentGrid
```
public void refreshCurrentGrid()
```
  - getLastPastEntries
```
public List<HistoryEntry> getLastPastEntries(int count)
```
  - undoRedo
```
public GridPreservation undoRedo(long lastDoneEntryID)
                          throws OperationException
```
    Rewinds or brings the history forward.
    
    Parameters:
    
    lastDoneEntryID - the id of the last change to be performed before the desired state of the project. Use 0L for the initial state.
    
    Returns:
    
    the degree to which the grid was preserved while changing the position in the history
    
    Throws:
    
    OperationException - if the application of changes required for this move did not succeed
  - getPrecedingEntryID
```
public long getPrecedingEntryID(long entryID)
```
    Given an history entry id, return the id of the preceding history entry, or -1 if there is none.
  - dispose
```
public void dispose()
```
    Uncaches all grids from memory and stops all related fetching and caching processes.
  - entryIndex
```
public int entryIndex(long entryID)
```
    Return the position of the history entry with the supplied id, or throws IllegalArgumentException if that id cannot be found.
  - getEntry
```
protected HistoryEntry getEntry(long entryID)
```

Class History

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

_projectId

_entries

_position

_cachedPosition

_desiredCachedPosition

_positionBeingCached

_cachingFuture

_cachingExecutorService

_steps

_dataStore

_gridStore

_lastModified

Constructor Detail

History

History

Method Detail

waitForCaching

getCurrentGrid

currentGridNeedsRefreshing

getInitialGrid

getGrid

getPosition

getCurrentEntryId

getCachedPosition

getEntries

getChangeDataStore

getGridCache

getLastModified

addEntry

addEntry

cacheGridOnDisk

uncacheGridFromDisk

updateCachedPosition

refreshCurrentGrid

getLastPastEntries

undoRedo

getPrecedingEntryID

dispose

entryIndex

getEntry