Scala – Abstract static methods in Scala

abstract classscalastatic methods

I've read this relevant post, but there weren't many concrete answers (poor language design more or less):
Why can't static methods be abstract in Java

I'm a bit of a newcomer to Scala, is this possible in it (maybe with traits or something)?

I tried having my base class extend a trait, but then child classes are required to implement the abstract static method as a member method, when I really want them to be required to be implemented in the companion object.

Best Answer

There aren't static methods in Scala [*], so your question is moot.

However, you can get what you want by extending an object with a trait:

scala> trait A { def foo(): Int }
defined trait A

scala> object C extends A { def foo(): Int = 5 }
defined module C

scala> C.foo
res0: Int = 5

which probably does what you want. There isn't really any way to force something to be implemented in the companion object of a class. The companion object might not exist.

[*] Technically, there are, but this is more of an implementation detail than an overall philosophy. See Method in companion object compiled into static methods in scala?

Related Solutions

Java – Can an abstract class have a constructor

Yes, an abstract class can have a constructor. Consider this:

abstract class Product { 
    int multiplyBy;
    public Product( int multiplyBy ) {
        this.multiplyBy = multiplyBy;
    }

    public int mutiply(int val) {
       return multiplyBy * val;
    }
}

class TimesTwo extends Product {
    public TimesTwo() {
        super(2);
    }
}

class TimesWhat extends Product {
    public TimesWhat(int what) {
        super(what);
    }
}

The superclass Product is abstract and has a constructor. The concrete class TimesTwo has a constructor that just hardcodes the value 2. The concrete class TimesWhat has a constructor that allows the caller to specify the value.

Abstract constructors will frequently be used to enforce class constraints or invariants such as the minimum fields required to setup the class.

NOTE: As there is no default (or no-arg) constructor in the parent abstract class, the constructor used in subclass must explicitly call the parent constructor.

Java – Why can’t static methods be abstract in Java

Because "abstract" means: "Implements no functionality", and "static" means: "There is functionality even if you don't have an object instance". And that's a logical contradiction.

Best Answer

Related Solutions

Java – Can an abstract class have a constructor

Java – Why can’t static methods be abstract in Java

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