In Google Adwords API, this is the Java code to get the budget id:
Long budgetId = budgetService.mutate(new BudgetOperation[] {budgetOperation}).getValue(0).getBudgetId();
I need to convert this to Scala code as I am working with Google AdWords API in Scala.
The transformation to Scala is pretty straightforward: immutable variables start with val; you can drop the type specification (it's inferred), and instantiating arrays is not a special case, but is just like instantiating a List or Map, etc.
val budgetId = budgetService.mutate(Array(budgetOperation)).getValue(0).getBudgetId()
The IntelliJ Scala plugin has a feature that will attempt to automatically convert Java code to Scala. While it doesn't always get it right, it may be of aid in learning how to map Java constructs into Scala.
Related
I'm looking to precompile a filter predicate to use over a large collection of data. Specifically, I will be dynamically decoding a protobuf object by the user provided String classname and allowing users to generate a predicate based on a String path into the underlying object. Ex "foo.bar.baz == 2" might compile to a bit of code like
class Filter {
def test(in: Array[Byte]) = {
Foo.parseFrom(in).getBar.baz == 2
}
}
There seem to be several options in Scala for precompiling code. You can use macros, you can use Scalameta, there seems to be talks of a new Dotty compiler for scala3, you could also use some Java just in time compilers. My question is, what is the most future-proof method of codegen filter predicates in Scala? We currently use 2.12. I don't want to write complex filter generation code that is going to be phased out in newer versions of Scala.
I'm experimenting with calcite from scala, and trying to pass a simple scala class for creating a schema at runtime (using ReflectiveSchema), I'm having some headache.
For example, re-implementing the FoodMart JDBC Example (which works well in Java), I'm calling it as simple as new ReflectiveSchema(new Hr()), using a Hr class rewritten in scala as:
class HR {
val emps: Array[Employee] = Array(new Employee(100, "Bill"))
}
I'm experiencing an error: ...SqlValidatorException: Object 'emps' not found within 'hr'. This problem seems to be related to the fact that val fields are actually created private in bytecode from java, and the implementation in calcite seems to be able to use (by means of java reflection) only fields accessible through the .getFields() method of a class.
So I suppose this direction requires a lot more hacking than a simple my_field.setAccessible(true) or similar.
Are there any other way to construct a schema by API, avoiding reflection and the usage of JSON?
thanks in advance for any suggestion
class Wish{
val s = "Hello! User. Wish you a Great day."
}
object Wish{
def main(args: Array[String]){
val w = new Wish()
println("Value - " + w.s )
}
}
Java classes can be used in Scala. Similarly, can Scala classes be used in Java?
Yes, Scala classes can be called from Java and vice versa.
The below text is taken from: Scala FAQs
What does it mean that Scala is compatible with Java?
The standard Scala backend is a Java VM. Scala classes are Java classes, and vice versa. You can call the methods of either language from methods in the other one. You can extend Java classes in Scala, and vice versa. The main limitation is that some Scala features do not have equivalents in Java, for example traits.
The following post also could be helpful to you: how to call Scala from Java
Yes. If you want to do this, there are a few things you might want to remember:
Do not use operators in your method names or provide a wordy alternative. Operator names can be called from Java but are mangled into somethings very ugly.
Java users might expect Java style getters and setters. You can produce those automatically by adding #BeanProperty annotation to fields.
In the same way Java user might be accustomed to factory methods called ClassName.of where Scala uses .apply. Those you have to provide by hand, if you want to provide that service.
I am getting the above mentioned Error from Scala compiler.
I am quite new to Scala and experimenting with it by converting a Java project that I have, to Scala. In my Java project, I am using Apache 'commons-chain' and I have a class that is extending 'org.apache.commons.chain.impl.ContextBase' and I am getting this error for it. I searched the internet it seems this problem has something to do with type erasure but my class doesn't not do anything special, just inherits from this class.
class SpecialContext extends ContextBase {
}
and here is the exact error I get..
Error:(10, 7) illegal inheritance;
class SpecialContext inherits different type instances of trait Map:
java.util.Map[K,V] and java.util.Map[K,V]
class SpecialContext extends ContextBase {
One of the attractions of Scala for me, while I can use nice language features of Scala, I would be still able to use the extensive number of open source libraries of the Java. After this experience, I am questioning this fact, considering my class not doing anything special, is it always this problematic to integrate the Java world and Scala world.
First my question is off-course is there a solution for the problem I described above?
Second question is, how is your experience integrating Scala and Java libraries? Or am I following the wrong way, are there ports of the popular Java libraries to Scala, like command-chain here, or lets say Spring....
Thx for answers.
The problem with ContextChain is that it uses raw types: in https://commons.apache.org/proper/commons-chain/apidocs/org/apache/commons/chain/impl/ContextBase.html you can see Map and HashMap instead of Map<Something, Something>.
Java only supports raw types to integrate with old, pre-generics code (to remind you, Java 5 was released in 2004), so you shouldn't see them in modern Java libraries. Scala doesn't support them at all.
In groovy one can do:
class Foo {
Integer a,b
}
Map map = [a:1,b:2]
def foo = new Foo(map) // map expanded, object created
I understand that Scala is not in any sense of the word, Groovy, but am wondering if map expansion in this context is supported
Simplistically, I tried and failed with:
case class Foo(a:Int, b:Int)
val map = Map("a"-> 1, "b"-> 2)
Foo(map: _*) // no dice, always applied to first property
A related thread that shows possible solutions to the problem.
Now, from what I've been able to dig up, as of Scala 2.9.1 at least, reflection in regard to case classes is basically a no-op. The net effect then appears to be that one is forced into some form of manual object creation, which, given the power of Scala, is somewhat ironic.
I should mention that the use case involves the servlet request parameters map. Specifically, using Lift, Play, Spray, Scalatra, etc., I would like to take the sanitized params map (filtered via routing layer) and bind it to a target case class instance without needing to manually create the object, nor specify its types. This would require "reliable" reflection and implicits like "str2Date" to handle type conversion errors.
Perhaps in 2.10 with the new reflection library, implementing the above will be cake. Only 2 months into Scala, so just scratching the surface; I do not see any straightforward way to pull this off right now (for seasoned Scala developers, maybe doable)
Well, the good news is that Scala's Product interface, implemented by all case classes, actually doesn't make this very hard to do. I'm the author of a Scala serialization library called Salat that supplies some utilities for using pickled Scala signatures to get typed field information
https://github.com/novus/salat - check out some of the utilities in the salat-util package.
Actually, I think this is something that Salat should do - what a good idea.
Re: D.C. Sobral's point about the impossibility of verifying params at compile time - point taken, but in practice this should work at runtime just like deserializing anything else with no guarantees about structure, like JSON or a Mongo DBObject. Also, Salat has utilities to leverage default args where supplied.
This is not possible, because it is impossible to verify at compile time that all parameters were passed in that map.