Question on generics - from Niko questions

[Anuradha Prasanna]

class Test {
void say(Set<Double> set) { }
void say(Set<Boolean> set) { }
}

When i try to compile the above code, it fails.
say(Set<Double> set) and say(Set<Boolean> set) is not a valid overload??
can any one explain why?

also,

can anyone explain, why the instanceof examples below give compiler error???

a)

Object set = new TreeSet<Integer>();
    boolean flag = set instanceof NavigableSet<Integer>;

b)

public class Child<T> {
   Child(T my){
boolean b = (my instanceof T);

[Ankit Garg]

As you might know, generics is only for compile time type safety. The JVM doesn't know about generics. So if you create a List<String>, to the JVM its the same as List without any types. That's why when you write two methods like

class Test {
void say(Set<Double> set) { }
void say(Set<Boolean> set) { }
}

Here after type erasure both the methods will have the same signature, so there is no overloading and thus you get an error. You can find more details about overloading here and about instanceof here...

[Anuradha Prasanna]

thanks Ankit, i will look into it..