Hive Generic UDF : multiply input integer by two

UDFMultiplyByTwo.java

import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector.Category;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector.PrimitiveCategory;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.io.IntWritable;

public class UDFMultiplyByTwo extends GenericUDF {
    PrimitiveObjectInspector inputOI;
    PrimitiveObjectInspector outputOI;

    public ObjectInspector initialize(ObjectInspector[] args) throws UDFArgumentException {
        assert (args.length == 1); // This UDF accepts one argument
        assert(args[0].getCategory() == Category.PRIMITIVE); // The first argument is a primitive type

        inputOI  = (PrimitiveObjectInspector)args[0];
        /* We only support INTEGER type */
        assert(inputOI.getPrimitiveCategory() == PrimitiveCategory.INT);

        /* And we'll return a type int, so let's return the corresponding object inspector */
        outputOI = PrimitiveObjectInspectorFactory.writableIntObjectInspector;
        
        return outputOI;
    }

    public Object evaluate(DeferredObject[] args) throws HiveException {
        if (args.length != 1) return null;

        // Access the deferred value. Hive passes the arguments as "deferred" objects 
        // to avoid some computations if we don't actually need some of the values
        Object oin = args[0].get();

        if (oin == null) return null;

        int value = (Integer) inputOI.getPrimitiveJavaObject(oin); 
        
        int output = value * 2;
        return new IntWritable(output);
    }

    @Override
    public String getDisplayString(String[] args) {
        return "Here, write a nice description";
    }
}