Problem with return type in an overriden method

[Xavier Figueroa]

Given this code:

class Animal {
    public Object voice(){
        return "animal voice";
     }
}

class Dog extends Animal{
    public String voice(){
        return "bark";
    }
}
public class CastingTest {
    public static void main(String[] args) {
        Animal a = new Dog();
        String s = a.voice();
        System.out.println(s);
    }
}

if i run this code i get

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - incompatible types
  required: java.lang.String
  found:    java.lang.Object

Why I need to cast (String)a.voice() if the method called is a Dog Class member and has a String return type?
if i put the cast, y get

bark

[Martin Vajsar]

You've declared the variable as Animal, and Animal.voice() returns Object. Although you know that the variable a contains an instance of Dog, the compiler does not "know" it and therefore expects that a.voice() returns Object.

This behavior of the compiler is not an error, it was designed this way. This is a trivial case. However, there might be cases in which such conclusions about actual type of a variable (if at all possible) might require extensive analysis. Therefore, the compiler follows a simple rule: a type of the variable is always determined by its declared type, regardless of its actual contents.

[Martin Vajsar]

... and welcome to the Ranch!

[Xavier Figueroa]

Thank you so much for your answer, I really needed this clarification and thanks for your Welcome