Elementary inheritance in java

Question

So I have a Superclass and two classes ClassA and ClassB that extend Superclass. ClassA and Superclass contain a method .doSomething(), ClassB does not. I got instances of ClassA and -B in a List<Superclass> objects. There also is a loop that iterates through objects and calls .doSomething() like this:

for(Superclass o : objects){
    o.doSomething();
}

My question is: If o is an instance if ClassA, is then ClassA.doSomething() being called or does this loop only call Superclass.doSomething()?

If there was only a possibility to _simply try it_. Hint: `ClassA.doSomething()` is called. — Marvin, Nov 04 '17 at 15:08
The overriden version will always be the one that's used, so yes, it'll be `ClassA.doSomething()` — user184994, Nov 04 '17 at 15:08
@Marvin 1. we don't know whether `doSomething()` is actually overrided in `ClassA`. 2. If it is, we don't know whether the implementation also invokes the method of the super class. — davidxxx, Nov 04 '17 at 15:22
@davidxxx 1. *"ClassA and Superclass contain a method .doSomething()"*, this statement tells us that `ClassA` has `doSomething` and it is therefore an overrode. 2. This is a valid point. Although, the question title should indicate that this corner case is not what the OP is asking for. — Chetan Kinger, Nov 04 '17 at 15:25
#1 is IMHO clearly stated in the question and #2 doesn't change the fact that the loop does **not** _"only call `Superclass.doSomething()`"_. — Marvin, Nov 04 '17 at 15:34

score 1 · Answer 1 · answered Nov 04 '17 at 15:10

1

Yes, because SuperClass implements doSomething, ClassB inherits that implementation, ClassA overrides it.

answered Nov 04 '17 at 15:10

Robert Moskal

21,737
8
62
86

score 0 · Answer 2 · answered Nov 04 '17 at 15:08

0

Yes, as the method .doSomething() of ClassA overrides the one of Superclass.

answered Nov 04 '17 at 15:08

flogy

906
4
16

score 0 · Answer 3 · answered Nov 04 '17 at 15:15

  class Super
{
 void hi()
 {
 System.out.println("Super class");
 }
}
class A extends Super
{
 void hi()
 {
  System.out.println("Class A");
 }

}
class B extends Super
{


}
public class Drive
{

public static void main(String[]args)
{
 Super s=new A(); 
 s.hi();                // prints "Class A"
 Super h=new B();
 h.hi();             // prints "Super Class" since B does not override Super
}
}                        //hope this helps

score 0 · Answer 4 · answered Nov 04 '17 at 16:14

If an instance is of ClassA, then its method will be called, and superclass methods will only be consireded if ClassA doesn't have an implementation.

And this doesn't change if you assign the ClassA instance to a variable of a superclass type. In other languages, that might be different, but with Java it's always like that.

Elementary inheritance in java

4 Answers4