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  1.  
  2. // source http://stackoverflow.com/q/12894335/348975
  3.  
  4. import java.util.List;
  5. import java.util.ArrayList;
  6.  
  7. class Main
  8. {
  9. 	public static void main ( String [ ] args )
  10. 	{
  11. 	}
  12. }
  13.  
  14. interface Canine {}
  15. class Dog implements Canine {}
  16. class Collie extends Dog {
  17.     public static void main(String[] args){
  18.         List<Dog> d = new ArrayList<Dog>();
  19.         List<Collie> c = new ArrayList<Collie>();
  20.         d.add(new Collie());
  21.         c.add(new Collie());
  22.         do1(d); do1(c);
  23.         do2(d); do2(c);
  24.     }
  25.     static void do1(List<? extends Dog> d2){
  26.  //       d2.add(new Collie());
  27.         System.out.print(d2.size());
  28.     }
  29.     static void do2(List<? super Collie> c2){
  30.         c2.add(new Collie());
  31.         System.out.print(c2.size());
  32.         System . out . println ( c2 . get ( 0 ) ) ; // works ok 
  33.         Collie collie = c2 . get ( 0 ) ; // compiler error ... no access
  34. 	System . out . println ( collie ) ;
  35.     }
  36. }
  37.  
Compilation error #stdin compilation error #stdout 0.06s 215488KB
comments (?)
stdin
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Standard input is empty
compilation info 
Main.java:33: error: incompatible types
        Collie collie = c2 . get ( 0 ) ; // compiler error ... no access
                                 ^
  required: Collie
  found:    CAP#1
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Object super: Collie from capture of ? super Collie
1 error
stdout
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Standard output is empty
https://ideone.com/msMcQ
language:
Java (12.0.1)
created:
11 years ago
visibility:
public

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