Java classes and Member objects type

Question

I have a bit of confusion in the following:

class Foo{
private ArrayList<Obj1> obj1List;
private ArrayList<Obj2> obj2List;


/* constructor */
...

public void push(?){

if(the object is of type Obj1)
    push into obj1List (object)
if(the object is of type Obj2)
    push into obj2List (object)

}

How can I do such a thing with the Push function, that it would identify the object type itself, without using instanceof (casting) or using (Object obj) as its' parameter? I need to it to know into which arraylist to push!

Answer 1

The easiest method is to have two overloads:

public void push(Obj1 obj) {
  objList1.add(obj);
}

public void push(Obj2 obj) {
  objList2.add(obj);
}

Answer 2

You can simply have 2 methods, one for each object type, and your program will use the method that is the most specific automatically:

public void push(Obj1 obj){
    obj1List.add(obj);
}

public void push(Obj2 obj){
    obj2List.add(obj);
}