Reference type casting doubt?

[Joe San]

Hi Guys,

The following is from Dan chisholm,

interface I1 {}  interface I2 {}
class Base implements I1 {}
class Sub extends Base implements I2 {}
class Gray {
  public static void main(String []args) {
  Base[] base = {new Base()};  // 1
  Sub sub[] = {new Sub()};     // 2
  Object obj = sub;            // 3
  base = obj;                  // 4
}}

The question is on which line will it give a compile time error? Answer given as line 4. Help my why?

Thanks in advance.

[Tommaso Nuccio]

Hi,

my answer is:
you could call base.methods() on an obj of type Object.
This wouldn't work, as the Object class does not know about base.methods.

E.G.:
class Base implements I1 {
public void methodA(){}
}

now you want base to be obj, which in turn references to sub.
Doesn't work.
Cast it:
--> base = (Base[]) obj;

[Arpit Khandelwal]

Hi Jothi Shankar ,

I think your current problem has nothing to do with all the interfaces and every other thing...

Its as simple as this ::
This will work ->class test {
public static void main(String args[]) {
Object obj = new Object();
test t = new test();
obj = t;
}
}

But this certainly wont ->
class test {

public static void main(String args[]) {

Object obj = new Object();
test t = new test();
t = obj;
}
}

You should know the very basic principle and that spells :: "you can not assign a parent reference to a child class " and Object class is the parent of all classes ,thats it.

I hope this satisfies you...

[Maneessh saxena]

Hi jyoti,
You’ll need typecast explicitely to get your code compile.see below.

interface I1 {} interface I2 {}
class Base implements I1 {}
class Sub extends Base implements I2 {}
class Gray {
public static void main(String []args) {
Base[] base = {new Base()}; // 1
Sub sub[] = {new Sub()}; // 2
Object obj = sub; // 3
base = (Sub[]) obj; /*or base = (Base[]) obj; */ //explicit typecasting
}}

Hope this will help.

Regards
Maneesh Saxena