org.apache.flink.api.java.functions

Annotation Type FunctionAnnotation.ConstantFields

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

This annotation declares that a function leaves certain fields of its input values unmodified and only "forwards" or "copies" them to the return value. The annotation is applicable to unary functions, like for example RichMapFunction, RichReduceFunction, or RichFlatMapFunction.

The following example illustrates a function that keeps the tuple's field zero constant:

 \@ConstantFields("0")
 public class MyMapper extends MapFunction, Tuple2>
 {
     public Tuple2 map(Tuple3 value) {
         return new Tuple2(value.f0, value.f1 * 0.5);
     }
 }
 

(Note that you could equivalently write @ConstantFields("0 -> 0").

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

If neither this annotation, nor the FunctionAnnotation.ConstantFieldsExcept 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