org.apache.flink.api.java.functions

Annotation Type FunctionAnnotation.ConstantFieldsFirst

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

This annotation declares that a function leaves certain fields of its first input values unmodified and only "forwards" or "copies" them to the return value. The annotation is applicable to binary functions, like for example RichFlatJoinFunction, RichCoGroupFunction, or RichCrossFunction.

The following example illustrates a join function that copies fields from the first and second input to the return value:

 \@ConstantFieldsFirst("1 -> 0")
 \@ConstantFieldsFirst("1 -> 1")
 public class MyJoin extends JoinFunction, Tuple2, Tuple2>
 {
     public Tuple2 map(Tuple2 first, Tuple2 second) {
         return new Tuple2(first.f1, second.f1);
     }
 }
 

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

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

See Also:

FunctionAnnotation.ConstantFieldsSecond, FunctionAnnotation.ConstantFields

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String[]	value

Element Detail

value

public abstract String[] value