Oh you need to call tf.constant, not Constant directly.
import org.tensorflow.op.Ops;
import org.tensorflow.op.core.Constant;

Ops tf = Ops.create(); // this will use default eager session, but you might want to create a graph instead?

val test12: Constant[TFloat64] = tf.constant(array_data);

The Ops instance is the entry point for creating all ops