Package com.singularsys.jep.functions

Interface ZeroLengthBehaviourI

All Superinterfaces:
Serializable
All Known Subinterfaces:
ZeroLengthBehaviourI.DefaultZeroLengthBehaviourI
All Known Implementing Classes:
ArrayFunctionBase, Average, BigDecVSum, ElementOf, First, Fold, Get, Last, MatrixDictGet, MatrixDictPut, MinMax, StreamCar, StreamFirst, StreamFold, StreamLast, StreamMinMax, StreamTerminalNaryBinaryFunction, TerminalNaryBinaryFunction, VSum, ZeroLengthBehaviourI.ZeroLengthHelper
public interface ZeroLengthBehaviourI extends Serializable
Interface for functions which can be configured to respond to zero length array arguments with either an exception, NaN or a value.

A standard template for implementing classes is 

public class MyFunction extends UnaryFunction implements ZeroLengthBehaviourI {
    ZeroLengthErrorBehaviour zeroLengthErrorBehaviour = ZeroLengthErrorBehaviour.EXCEPTION;
    Object zeroLengthValue = null;

    @Override
    public ZeroLengthErrorBehaviour getZeroLengthErrorBehaviour() {
        return zeroLengthErrorBehaviour;
    }
    @Override
    public void setZeroLengthErrorBehaviour(
        ZeroLengthErrorBehaviour zeroLengthErrorBehaviour) {
        this.zeroLengthErrorBehaviour = zeroLengthErrorBehaviour;
     }
     @Override
     public Object getZeroLengthValue() {
         return zeroLengthValue;
     }
     @Override
     public void setZeroLengthValue(Object zeroLengthValue) {
         this.zeroLengthValue = zeroLengthValue;
     }

     @Override
     public Object eval(Object arg) throws EvaluationException {
         boolean empty;
         Object res;
         // code to calculate result, sets the empty flag and the res value
         if(empty) {
             return zeroLengthResultOrException(getName());
         }
         return res;
     }
 }
Alternatively if you use an Optional: 
@Override
public Object eval(Object arg) throws EvaluationException {
    Optional<Object> res = doCalc(arg);
    return getValueOrException(getName(), res);
}

Which will return the value if present, or if not present, either return the zero length values or throws an exception

The ZeroLengthBehaviourI.DefaultZeroLengthBehaviourI simplifies the implementation of implementing classes by delegating the zero length behaviour to a ZeroLengthBehaviourI.ZeroLengthHelper class. 

public class MyFunction extends UnaryFunction implements JepComponent, DefaultZeroLengthBehaviourI {
    ZeroLengthHelper zeroLengthHelper = new ZeroLengthHelper();
    @Override
    public ZeroLengthBehaviourI getZeroLengthHelper() {
        return zeroLengthHelper;
    }

     @Override
     public Object eval(Object arg) throws EvaluationException {
         Optional<Object> res = doCalc(arg);
         return getValueOrException(getName(), res);
     }

     @Override
     public JepComponent getLightWeightInstance() {
         var res = new MyFunction();
         res.zeroLengthHelper.setZeroLengthBehaviourAndValue(zeroLengthHelper);
         return res;
     }
 }
Since:
Jep 4.1

  • Method Details

    • getZeroLengthErrorBehaviour

      ZeroLengthBehaviourI.ZeroLengthErrorBehaviour getZeroLengthErrorBehaviour()
      Gets how to respond to arguments with zero length arrays.
      Returns:
      either EXCEPTION, NAN or VALUE

    • setZeroLengthErrorBehaviour

      void setZeroLengthErrorBehaviour(ZeroLengthBehaviourI.ZeroLengthErrorBehaviour zeroLengthErrorBehaviour)
      Sets how to respond to arguments with zero length arrays. Either an Exception is thrown or NaN is returned.
      Parameters:
      zeroLengthErrorBehaviour - either EXCEPTION, NAN or VALUE

    • getZeroLengthValue

      Object getZeroLengthValue()
      Gets the value to be returned when a zero length array is passed as an argument and the zero length error behaviour is set to VALUE.
      Returns:
      the value, null by default

    • setZeroLengthValue

      void setZeroLengthValue(Object zeroLengthValue)
      Sets the value to be returned when a zero length array is passed and the zero length error behaviour is set to VALUE. The setZeroLengthErrorBehaviour(ZeroLengthErrorBehaviour) method should be used to set the zero length error behaviour to VALUE.
      Parameters:
      zeroLengthValue - the value to return when a zero length array is passed

    • zeroLengthResultOrException

      default Object zeroLengthResultOrException(String functionName) throws EvaluationException
      Either return the value for zero length array or throws an exception depending on the zero length error behaviour flag.
      Parameters:
      functionName -
      Returns:
      either NaN, the value set by setZeroLengthValue
      Throws:
      EvaluationException - if the zero length error behaviour is set to EXCEPTION

    • getErrorMessage

      default String getErrorMessage(String functionName)
      Gets the zero length error message. The default implementation format a string using the functions.AtLestOneArgumentIsRequired property.
      Parameters:
      functionName - name of the function passed into zeroLengthResultOrException(String)
      Returns:
      the error message.

    • getValueOrException

      default Object getValueOrException(String functionName, Optional<Object> value) throws EvaluationException
      Either return the optional's value or, if not present, either return the zero length values or throws an exception depending on the zero length error behaviour flag.
      Parameters:
      functionName - name of function used in exception message if thrown
      value - the value to return if present
      Returns:
      the optional value, or default value
      Throws:
      EvaluationException - if value is not present and the zero length error behaviour is set to EXCEPTION