I have in one scala file following class (and bellow main method):
class OuterClass {
class Inner {
def innerMethod(): Unit = {
println("innerMethod")
}
class InnerMost {
innerMethod()
}
}
}
Now want to call that class from main method:
object main {
def main (args: Array[String] ): Unit = {
println("Main")
val pt = new OuterClass
...
}
}
How to achieve that?
To instantiate the nested class Inner and then InnerMost
val pti = new pt.Inner
val ptim = new pti.InnerMost
Related
I need to write two functions to get the output format and the output index for file conversion. As part of this, I wrote a TransformSettings class for these methods and set the default value. And in the transformer class, I created a new object of TransformSettings class to get the default values for each job run. Also, I have another class called ParquetTransformer that extends Transformer where I want to change these default values. So I implemented like below.
class TransformSettings{
def getOuputFormat: String = {
"orc"
}
def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("orc.column.index.access")
}
}
class Transformer{
def getTransformSettings: TransformSettings = {
new TransformSettings
}
def posttransform(table: AWSGlueDDL.Table):Dateframe ={
val indexAccess = getTransformSettings.getOuputIndex(table: AWSGlueDDL.Table)
........
}
}
class ParquetTransformer extends Transformer{
override def getTransformSettings: TransformSettings = {
val transformSettings = new TransformSettings {
override def getOuputFormat: String = {
"parquet"
}
override def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("parquet.column.index.access")
}
}
}
}
Is there a way to avoid creating a brand new object of TransformSettings in Transfomer class every time this is called?
Also is there a way to rewrite the code using Scala value class?
As #Dima proposed in the comments try to make TransformSettings a field / constructor parameter (a val) in the class Transformer and instantiate them outside
class TransformSettings{
def getOuputFormat: String = {
"orc"
}
def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("orc.column.index.access")
}
}
class Transformer(val transformSettings: TransformSettings) {
def posttransform(table: AWSGlueDDL.Table): DataFrame ={
val indexAccess = transformSettings.getOuputIndex(table: AWSGlueDDL.Table)
???
}
}
val parquetTransformSettings = new TransformSettings {
override def getOuputFormat: String = {
"parquet"
}
override def getOuputIndex(table: AWSGlueDDL.Table): Option[String] = {
table.StorageDescriptor.SerdeInfo.Parameters.get("parquet.column.index.access")
}
}
class ParquetTransformer extends Transformer(parquetTransformSettings)
You don't seem to need value classes (... extends AnyVal) now. They are more about unboxing, not about life-cycle management. TransformSettings and Transformer can't be value classes because they are not final (you're extending them in class ParquetTransformer extends Transformer... and new TransformSettings { ... }). By the way, value classes have many limatations
https://failex.blogspot.com/2017/04/the-high-cost-of-anyval-subclasses.html
https://github.com/scala/bug/issues/12271
Besides value classes, there are scala-newtype library in Scala 2 and opaque types in Scala 3.
I have the following test:
class Foo extends mutable.SpecificationWithJUnit {
sequential
"this example should run before the 'After' method" in new Context {
bar must beSome
}
class Context extends mutable.BeforeAfter with mutable.Around {
override def apply[T : AsResult](a: =>T): Result = {
lazy val result = super[Around].apply(a)
super[BeforeAfter].apply(result)
}
override def delayedInit(x: => Unit): Unit = around { try { before; x; Success() } finally { after }}
#Resource var barReader : BarReader = _
val bar = barReader.someBar
override def before : Any = { //some stuff}
def after: Any = {
bar = None
}
override def around[T : AsResult](t: =>T) = {
//spring context injection logic
AsResult.effectively(t)
}
}
}
}
I expect this test to pass but in reality what happens is that because of the delayed init, the after runs before the example. If I change the Context to a trait I lose the delayed init functionality. Is this a bug or am I doing something wrong?
**Edited:
This example will throw an NPE when the Context is a trait. What I expect to happen is that because of the delayed-init, the Context's constructor, which consequentially means the barReader.someBar will run only after the barReader has been injected.
Thanks
Netta
You should use a trait instead of a class for Context. If you use a class, delayedInit (hence after) will be triggered twice. Once for the body of the Context class and another time for the body of the anonymous class new Context. With a trait you don't get such a behavior:
class Foo extends mutable.SpecificationWithJUnit {
sequential
"this example should run before the 'After' method" in new Context {
bar must beSome
}
trait Context extends mutable.After {
var bar : Option[String] = Some("bar")
def after: Any = bar = None
}
}
Simple answer, looks like this can't be done.
As far as I understand it, Scala creates an anonymous class if I create a class using the new keyword and follow the class name with a constructor:
class MyClass {
def doStuff() {
// ...
}
}
val mc = new MyClass {
doStuff()
}
The nice thing being that all the code in the constructor is in the scope of the new object.
Is there a way I can reproduce this syntax where the class is created by a factory method rather than the new keyword? i.e. make the following code work:
val mf = new MyFactory
val mc = mf.MyClass {
doStuff()
}
I can't find a way to do it but Scala has so much to it that this might be pretty easy!
Using an import as suggested by #Ricky below I can get:
val mf = MyFactory;
val mc = mf.MyClass
{
import mc._
doStuff()
}
(Where the blank line before the block is needed) but that code block is not a constructor.
You can do this, but you still have to keep the new keyword, and create the nested class as a path-dependent type:
class Bippy(x: Int) {
class Bop {
def getIt = x
}
}
val bip = new Bippy(7)
val bop = new bip.Bop
bop.getIt // yields 7
val bop2 = new bip.Bop{ override def getIt = 42 }
bop2.getIt // yields 42
I don't think it's possible. However, a common pattern is to add a parameter to factory methods which takes a function modifying the created object:
trait MyClass {
var name = ""
def doStuff():Unit
}
class Foo extends MyClass {
def doStuff() { println("FOO: " + name) }
}
trait MyClassFactory {
def make: MyClass
def apply( body: MyClass => Unit ) = {
val mc = make
body(mc)
mc
}
}
object FooFactory extends MyClassFactory {
def make = new Foo
}
You can then create and modify instance with a syntax close to your example:
val foo = FooFactory { f=>
f.name = "Joe"
f.doStuff
}
It sounds like you're just looking to mix in a trait. Instead of calling myFactoryMethod(classOf[Foo]] which ideally would do (if Scala permitted it):
new T {
override def toString = "My implementation here."
}
you can instead write
trait MyImplementation {
override def toString = "My implementation here."
}
new Foo with MyImplementation
However, if you are just looking to get the members of the new object accessible without qualification, remember you can import from any stable identifier:
val foo = new Bar
import foo._
println(baz) //where baz is a member of foo.
I have a class, with multiple methods and members. When I create an instance of this class, I create an instance of another class within the first class. Some of the methods in this second class require to know which instance of the first class is running. Currently, I am trying to pass "this" into the argument that accepts type firstClass. What am I doing wrong? Again, I simply want the second class instance knowing what first class instance it belongs to so that it can call public methods and members from it.
EDIT: Code example:
def main(args:Array[String]) : Unit = {
val objectOne = new classOne
}
class classOne {
val mutableBuffer = mutable.Buffer[String]
val objectTwo = new classTwo
objectTwo.doThis(this)
}
class classTwo {
def doThis (exA:classOne) = {
exA.mutableBuffer += "Adding text to a Buffer in object One"
}
}
Self-typing is often the cleanest solution here
class Bippy {
outer =>
...
class Bop {
def demoMethod() = println(outer)
}
...
}
UPDATE
The example code changes everything, this clearly isn't about inner classes. I believe your problem is in this line:
val mutableBuffer = mutable.Buffer[String]
It isn't doing what you think it's doing, mutableBuffer is now pointing to the mutable.Buffer singleton, it isn't actually an instance of a Buffer
Instead, try one of these two:
val mutableBuffer = mutable.Buffer[String]()
//or
val mutableBuffer = mutable.Buffer.empty[String]
You should also stick to the convention of starting class/singleton/type names with an uppercase letter, turning your example code into:
import collection.mutable.Buffer
def main(args:Array[String]) : Unit = {
val one = new ClassOne()
}
class ClassOne {
val mutableBuffer = Buffer.empty[String]
val two = new ClassTwo()
two.doThis(this)
}
class ClassTwo {
def doThis(one: ClassOne) = {
one.mutableBuffer += "Adding text to a Buffer in object One"
}
}
I had to make some superficial changes to your example code in order to make it run:
import scala.collection.mutable
class classOne {
val mutableBuffer : mutable.Buffer[String] = new mutable.ArrayBuffer[String]
val objectTwo = new classTwo
objectTwo.doThis(this)
}
class classTwo {
def doThis (exA : classOne) = {
exA.mutableBuffer += "Adding text to a Buffer in object One"
}
}
val objectOne = new classOne
println(objectOne.mutableBuffer(0))
But it works as expected. The classTwo object is able to modify the classOne object. Do you need something beyond this functionality?
I am not a Groovy expert, but I did read the book "Groovy in Action". In Groovy, each closure comes with a "context", where the items inside the closure can get access to pseudo-variables like "this", "owner", and "delegate", that let the items know who called the closure. This allows one to write DSLs like this (from Groovy in Action):
swing = new SwingBuilder()
frame = swing.frame(title:'Demo') {
menuBar {
menu('File') {
menuItem 'New'
menuItem 'Open'
}
}
panel {
// ...
}
}
Note that 'menuBar' "knows" that it belongs to 'frame' because it can get context information about the owner and delegate of the closure.
Is this possible to do in Scala? If so, how?
One way is to use a scala.util.DynamicVariable to track the context. Something like the SwingBuilder could be implemented as
import scala.util.DynamicVariable
import javax.swing._
object SwingBuilder {
case class Context(frame: Option[JFrame], parent: Option[JComponent])
}
class SwingBuilder {
import SwingBuilder._
val context = new DynamicVariable[Context](Context(None,None))
def frame(title: String)(f: =>Unit) = {
val res = new JFrame(title)
res.add(new JPanel())
context.withValue(Context(Some(res),context.value.parent)){f;res}
}
def menuBar(f: =>Unit) = {
val mb = new JMenuBar()
context.value.frame.foreach(_.setJMenuBar(mb))
context.withValue(Context(context.value.frame,Some(mb))){f;mb}
}
def menu(title: String)(f: =>Unit) = {
val m = new JMenu(title)
context.value.parent.foreach(_.asInstanceOf[JMenuBar].add(m))
context.withValue(Context(context.value.frame,Some(m))){f;m}
}
def menuItem(title: String) = {
val mi = new JMenuItem(title)
context.value.parent.foreach(_.asInstanceOf[JMenu].add(mi))
}
}
object Test {
def main(args: Array[String]) {
val builder = new SwingBuilder()
import builder._
val f = frame("Demo") {
val mb = menuBar {
menu("File") {
menuItem("New")
menuItem("Open")
}
}
}
f.setVisible(true)
}
}