java - How to define a generic List in an abstract super class? -

i'm trying create abstract class abstract method, should able return type of list items extending superbean.

later want create generic class can add items lists. example:

class abstractservice<t extends superbean> {     //this i'm aiming     void add(t item) {         // "is not applicable arguments (t)"         superbean.getsublist().add(item);     } }  abstract class superbean {     abstract list<? extends superbean> getsublist(); }  class mybean1 extends superbean {     list<mybean2> sublist;      list<mybean2> getsublist() {         return sublist;     } }  class mybean2 extends superbean {     list<mybean3> sublist;      list<mybean3> getsublist() {             return sublist;         } } 

question: how have define abstract getsublist() class can add t item implementation of superbean?

you need add generics in abstractservice:

//        add s t's type parameter         add <s> superbean here class abstractservice<s extends superbean, t extends superbean<s>> {     // i'm assuming superbean defined here.     t superbean;      //this i'm aiming     void add(s item) {         superbean.getsublist().add(item);     } } 

next, need make superbean generic, subclasses defining generic type parameter <t>:

abstract class superbean<t extends superbean> {     // can define abstract method properly:     abstract list<t> getsublist(); } 

each subclass defines generic type parameter appropriately:

class mybean1 extends superbean<mybean2> {     list<mybean2> sublist;      list<mybean2> getsublist() {         return sublist;     } } 

and mybean2 defined similarly:

class mybean2 extends superbean<mybean3> {     list<mybean3> sublist;      list<mybean3> getsublist() {             return sublist;     } } 

this allows declare services follows:

abstractservice<mybean2, mybean1> service1 = new abstractservice<mybean2, mybean1>(); abstractservice<mybean3, mybean2> service2 = new abstractservice<mybean3, mybean2>();