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  1. import java.util.*;
  2.  
  3. class Builder<T extends Builder> {
  4.     private String name;
  5.     private List<String> friends;
  6.  
  7.     T setName(String name) {
  8.         this.name = name;
  9.         return (T) this;
  10.     }
  11.  
  12.     T setFriends(List<String> friends) {
  13.         this.friends = friends;
  14.         return (T) this;
  15.     }
  16.  
  17.     T uncheckedOops() {
  18.         // setName returns a raw type Builder
  19.         setName("Foobar")
  20.             // oops, passing List<Integer> to List<String> compiles,
  21.             // because the parameter type of T.setFriends is erased to just List
  22.             .setFriends(Arrays.asList(1, 2, 3));
  23.         return (T) this;
  24.     }
  25.  
  26.     public static void main(String[] args) {
  27.         Builder<?> b = new Builder<>().uncheckedOops();
  28.  
  29.         try {
  30.             for (String friend : b.friends)
  31.                 System.out.println(friend);
  32.         } catch (Exception x) {
  33.             x.printStackTrace(System.out);
  34.         }
  35.     }
  36. }
Success #stdin #stdout 0.07s 27704KB
comments (?)
stdin 
Standard input is empty
stdout 
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
	at Builder.main(Main.java:30)
https://ideone.com/xCeii8
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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