package demoThe above Scala Trait generates a Java Interface:
trait Trait1 {
def abstractMethod: Int
}
public interface demo.Trait1 {Now let us find out what happens when a Scala Trait has got an implemented method along with an abstract one.
public abstract int abstractMethod();
}
package demoThis one generates two Java entities:
trait Trait3 {
def abstractMethod: Int
def implMethod: Int = 7
}
public interface demo.Trait3 {
public abstract int abstractMethod();
public abstract int implMethod();
}
public abstract class demo.Trait3$class {So along with a sensible Java Interface, it also generated an abstract class with two static methods! Let us have a closer look at the first static method: it's name is same as the implemented method on the Trait and the default implementation logic is reflected too. But what's the use of this abstract class?
public static int implMethod(demo.Trait3);
Code:
0: bipush 7
2: ireturn
public static void $init$(demo.Trait3);
Code:
0: return
}
To understand how this abstract class is used let us use it, of course. :)
package demoAnd this is how it was used:
class SomeClass extends Trait3 {
def abstractMethod = 1
}
public class demo.SomeClass implements demo.Trait3 {The SomeClass implements the generated Java Interface, demo.Trait3. makes sense.
public int implMethod();
Code:
0: aload_0
1: invokestatic #17 // Method demo/Trait3$class.implMethod:(Ldemo/Trait3;)I
4: ireturn
public int abstractMethod();
Code:
0: iconst_1
1: ireturn
public demo.SomeClass();
Code:
0: aload_0
1: invokespecial #24 // Method java/lang/Object."<init>":()V
4: aload_0
5: invokestatic #28 // Method demo/Trait3$class.$init$:(Ldemo/Trait3;)V
8: return
}
But this class has also magically got the default implemented Scala Trait method, implMethod!
And how is this auto-generated method implemented? It simply delegates to the namesake static method in abstract class Trait3$class. No magic. Isn't it?
Wait a minute, if the generated Trait3$class has all static methods then what could have been the reason behind declaring it "abstract"? Please let me know when you find it. No, I am serious.
