Use of wildcard characters in Java generics

 PackageCom.srie.testjava;Importjava.util.ArrayList;Importjava.util.List; Public classTestclassdefine2<t, SextendsT> {     Public Static voidMain (string[] args) {List<String> slist =NewArraylist<string>(); List<Integer> iList =NewArraylist<integer>(); Ilist.add (1); Ilist.add (2); Slist.add (A); Slist.add ("B"); List<?> A =slist; System.out.println (a);//[A, b]//A.add ("C");//You cannot add specific elements to an indeterminate type, only from an indeterminate type;A.add (NULL);//can add null;Slist.add ("C"); System.out.println (a);//[A, B, c]A =iList; System.out.println (a);//[1, 2]//post-compilation results://List slist = new ArrayList (); //List iList = new ArrayList (); //Ilist.add (integer.valueof (1)); //Ilist.add (integer.valueof (2)); //Slist.add ("a"); //Slist.add ("B"); //List a = slist; //System.out.println (a); //        //a.add (NULL); //Slist.add ("C"); //System.out.println (a); //a = iList; //System.out.println (a);    }}

Use of wildcard characters in Java generics