How to override java list methods?

Question

I'm working on a java project where i need to use lists of different types that I create (Student ,school ... for example).

The problem is that I need to use some list methods with this types(or classes) like "containe" for Ex ...

I try to override this methods by creating my own list(arraylist or vector) which is Extended from java list ... but I have many problems because I want to use this new list(my list) with different types .

This how I extends myList from java list:

public class myList extends ArrayList<Object>{

public myList() {
}
    /***methods***/
}

and this how I use it :

public class newclass(){
       .
       .
       .
    myList<student> sl=new myList<student>();
       .
       .

But it does not work. So what is the right way to do this.

and thanks.

two sidenodes. Classes do start with capital letters following the java naming convention. second, don´t make this custom `List` a rawtype by defining the generic as `Object`, this will and can only cause troubles later on(which is also your problem). Make it `MyList extends ArrayList`. — SomeJavaGuy, Apr 25 '16 at 12:37
Possible duplicate of [Extending Generic Classes](http://stackoverflow.com/questions/7255643/extending-generic-classes) — Rabbit Guy, Apr 25 '16 at 12:37
I don't know if I understood correctly, but maybe all you need is implement comparable in your object, so sort and other methods work ... reference: http://stackoverflow.com/a/3718515/2101088 — Rodrigo, Apr 25 '16 at 12:42

Nicolas Filotto · Accepted Answer · 2016-04-25T18:52:35.447

1

What you are looking for are Generics:

public class myList<T> extends ArrayList<T> {
...
}

This way you can create your own list of whatever you want like this:

myList<student> sl = new myList<>();

Response Update:

how to make get -for example- return the same type in declaration -which is instead of the type Object

Response with your list

myList<student> sl = new myList<>();
sl.add(new student());
student s = sl.get(0);

Response with an ArrayList:

// But it works also with an ArrayList which implicitly mean that you have no need 
// to create your own implementation of an ArrayList
List<student> sl = new ArrayList<>();
sl.add(new student());
student s = sl.get(0);

edited Apr 25 '16 at 18:52

answered Apr 25 '16 at 12:48

Nicolas Filotto

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Can you please write the overrided `contain` for a type(object) `student` wich is defined by `String firstName ; String lastName;`. – M. os.i Apr 25 '16 at 14:27
could you please clarify I don't understand your question – Nicolas Filotto Apr 25 '16 at 14:33
1

you have no need to override the contains method, simply implement properly your equals method in your class student – Nicolas Filotto Apr 25 '16 at 15:06
i want to override the methods of list (contain,get ...) to work with different types of objects (i.e how to make `get` -for example- return the same type in declaration -which is `` instead of the type `Object`) , so how to do this ?! @NicolasFilotto – M. os.i Apr 25 '16 at 18:30
Maybe you want to overload by adding public boolean contains(T element) and then your class definition will be something like public class myList extends ArrayList – Nicolas Filotto Apr 25 '16 at 18:42
@M.os.i answer updated, once again you have no need to create your own imp of an ArrayList – Nicolas Filotto Apr 25 '16 at 18:52

How to override java list methods?

1 Answers1