15:44 java: incompatible types: org.apache.beam.sdk.values.POutput cannot be converted to org.apache.beam.sdk.values.PCollection

Question

The code below is mostly copy-pasted from the apache beam docs. Still not able to figure out this error. Also, I am trying to learn beam. Can somebody suggest some good tutorial/article to look upon?

import org.apache.beam.sdk.io.TextIO;
import org.apache.beam.sdk.transforms.MapElements;
import org.apache.beam.sdk.transforms.SimpleFunction;
import org.apache.beam.sdk.values.PCollection;


public class reports {
    public static void main(String[] args) {
        Pipeline p = Pipeline.create();
        PCollection<String> students = p.apply(TextIO.read().from("./students.csv"));
// error line below
        PCollection output = students.apply(MapElements.via(new calculatePercentage()));
        output.apply(TextIO.write().to("./reports.csv"));
        p.run();
    }
}
class calculatePercentage extends SimpleFunction{
    @Override
    public Object apply(Object input) {
        return input;
    }
}```

Answer 1

Specifying types for SimpleFunction Solved it. ?

class calculatePercentage extends SimpleFunction<String , String>{
}