無検査キャストの警告が出るけどジェネリクスで一応できた

class Super<E>{
E own = (E)this;
String a;
public E setA(String a){
this.a = a;
return own;
}}

class Sub extends Super<Sub>{
String c;
public Sub setC(String c){
this.c = c;
return own
}}

public class Test{
public static void main(String [] args){
Sub s = new Sub();
s.setA("this is a").setC("this is c");
System.out.println(s.getA());
System.out.println(s.getC());
}}