CODEWITHSUNDEEP
scalainheritancemethodsabstract-class
alepuzio
alepuzio

Reputation: 1418

"Abstract class does not take parameters": why?

I'm studying Scala and I'm trying to translate the code of some design pattern from Java to Scala, but I lose some detail.

For example, now I write a simple State but I receive three occurrences of the same error in compile time:

This is the code

abstract class Statelike {
    def writeName(STATE_CONTEXT : StateContext ,  NAME : String): Unit
 }

class StateA extends Statelike {
   override def writeName( STATE_CONTEXT : StateContext ,   NAME : String) : Unit = {
        println(NAME.toLowerCase());
        STATE_CONTEXT.myState(new StateB)  **//same error**
    }
}//end StateA 


class StateB  extends Statelike {
     var count = 0;
     override def writeName( state_contest: StateContext , name: String) : Unit = {
     println(name.toUpperCase());
     count+1;
     var conto2 = count;
     if (conto2 > 1) {
        state_contest.myState(new StateA)     **//same error**
     }
    }
}//StateB  

class StateContext {

    var state : Statelike = null

    def StateContext() {
        myState(new StateA)   **//same error**
    }

    def myState_=(s1 : Statelike ) = {state = s1}

    def myState : Statelike = state

    def writeName ( NAME : String): Unit =  {
        myState.writeName(this, NAME);
    }
}//end StateContext 

object TestClientState {
    def main( args : Array[String]) { 
        var SC = new StateContext();

        SC.writeName("Monday");
        SC.writeName("Tuesday");
        SC.writeName("Wednesday");
        SC.writeName("Thursday");
        SC.writeName("Friday");
        SC.writeName("Saturday");
        SC.writeName("Sunday");
    }
}

The error occurences are:

State.scala:12: error: Statelike does not take parameters
        STATE_CONTEXT.myState(new StateB)
                             ^
State.scala:26: error: Statelike does not take parameters
            state_contest.myState(new StateA)
                                 ^
State.scala:37: error: Statelike does not take parameters
        myState(new StateA)
               ^
three errors found

reading the doc, it likes an uncorrect use of traits, but I'm not using the traits!

The StateA and StateB are the implementing class of class Statelike, what is abstract. No more, no less.

Where's my code error? A too much "Java-style" inheritance? Waht can be a solution?

Thanks in advance

Upvotes: 0

Views: 360

Answers (1)

senia
senia

Reputation: 38045

Compiler is puzzled what you are trying to do here:

myState(new StateA)

Well... I'm puzzled too. myState is a method without parameters.

def myState : Statelike = state

So you could rewrite your code like this:

val ms: Statelike = myState
ms(new StateA)

Since ms is not a method the last line (ms(new StateA)) is the shorten version of ms.apply(new StateA). But there is no method apply in class Statelike.

Maybe you want to call myState.writeName(new StateA) instead of myState.(new StateA), but there is not enough parameters for method writeName.

Setter

As @AlexIv mentioned: If you are trying to call setter, you should note that it's name is myState_=, not myState.

myState_=(new StateA)

With syntax sugar:

myState = new StateA

Upvotes: 4

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