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## org.apache.poi.ss.formula.eval.forked
Class ForkedEvaluator

    java.lang.Object
      org.apache.poi.ss.formula.eval.forked.ForkedEvaluator

    public final class ForkedEvaluator

extends java.lang.Object

An alternative workbook evaluator that saves memory in situations where a single workbook is concurrently and independently evaluated many times. With standard formula evaluation, around 90% of memory consumption is due to loading of the `HSSFWorkbook` or `XSSFWorkbook`. This class enables a 'master workbook' to be loaded just once and shared between many evaluation clients. Each evaluation client creates its own `ForkedEvaluator` and can set cell values that will be used for local evaluations (and don't disturb evaluations on other evaluators).

Method Summary
`void` | `copyUpdatedCells(Workbook workbook)` Copies the values of all updated cells (modified by calls to `updateCell(String, int, int, ValueEval)`) to the supplied `workbook`. Typically, the supplied `workbook` is a writable copy of the 'master workbook', but at the very least it must contain sheets with the same names.
`static ForkedEvaluator` | `create(Workbook wb, IStabilityClassifier stabilityClassifier, UDFFinder udfFinder)`
`ValueEval` | `evaluate(java.lang.String sheetName, int rowIndex, int columnIndex)` If cell contains a formula, the formula is evaluated and returned, else the CellValue simply copies the appropriate cell value from the cell and also its cell type.
`static void` | `setupEnvironment(java.lang.String[] workbookNames, ForkedEvaluator[] evaluators)` Coordinates several formula evaluators together so that formulas that involve external references can be evaluated.
`void` | `updateCell(java.lang.String sheetName, int rowIndex, int columnIndex, ValueEval value)` Sets the specified cell to the supplied `value`

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

Method Detail

### create

    public static ForkedEvaluator create(Workbook wb,
                                         IStabilityClassifier stabilityClassifier,
                                         UDFFinder udfFinder)

  Parameters:
    `udfFinder` - pass `null` for default (AnalysisToolPak only)

### updateCell

    public void updateCell(java.lang.String sheetName,
                           int rowIndex,
                           int columnIndex,
                           ValueEval value)

  Sets the specified cell to the supplied `value`

  Parameters:
    `sheetName` - the name of the sheet containing the cell
    `rowIndex` - zero based
    `columnIndex` - zero based

### copyUpdatedCells

    public void copyUpdatedCells(Workbook workbook)

  Copies the values of all updated cells (modified by calls to `updateCell(String, int, int, ValueEval)`) to the supplied `workbook`.
  Typically, the supplied `workbook` is a writable copy of the 'master workbook', but at the very least it must contain sheets with the same names.

### evaluate

    public ValueEval evaluate(java.lang.String sheetName,
                              int rowIndex,
                              int columnIndex)

  If cell contains a formula, the formula is evaluated and returned, else the CellValue simply copies the appropriate cell value from the cell and also its cell type. This method should be preferred over evaluateInCell() when the call should not modify the contents of the original cell.

  Parameters:
    `sheetName` - the name of the sheet containing the cell
    `rowIndex` - zero based
    `columnIndex` - zero based
  Returns:
    `null` if the supplied cell is `null` or blank

### setupEnvironment

    public static void setupEnvironment(java.lang.String[] workbookNames,
                                        ForkedEvaluator[] evaluators)

  Coordinates several formula evaluators together so that formulas that involve external references can be evaluated.

  Parameters:
    `workbookNames` - the simple file names used to identify the workbooks in formulas with external links (for example "MyData.xls" as used in a formula "[MyData.xls]Sheet1!A1")
    `evaluators` - all evaluators for the full set of workbooks required by the formulas.

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Copyright 2017 The Apache Software Foundation or its licensors, as applicable.