org.apache.flink.api.java.functions

Annotation Type FunctionAnnotation.ConstantFieldsExcept

@Target(value=TYPE)
@Retention(value=RUNTIME)
public static @interface FunctionAnnotation.ConstantFieldsExcept

This annotation declares that a function changes certain fields of its input values, while leaving all others unmodified and in place in the return value. The annotation is applicable to unary functions, like for example RichMapFunction, RichReduceFunction, or RichFlatMapFunction.

The following example illustrates that at the example of a Map function:

 \@ConstantFieldsExcept("1")
 public class MyMapper extends MapFunction, Tuple3>
 {
     public Tuple3 map(Tuple3 value) {
         return new Tuple3(value.f0, value.f2 / 2, value.f2);
     }
 }
 

The annotation takes one String array specifying the positions of the input types that do not remain constant. When this annotation is used, it is assumed that all other values remain at the same position in input and output. To model more complex situations use the FunctionAnnotation.ConstantFieldss annotation.

This annotation is mutually exclusive with the FunctionAnnotation.ConstantFields annotation.

If neither this annotation, nor the FunctionAnnotation.ConstantFields annotation are set, it is assumed that no field in the input is forwarded/copied unmodified.

See Also:

FunctionAnnotation.ConstantFieldsExcept

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String[]	value

Element Detail

value

public abstract String[] value