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  1. import java.util.Optional;
  2. import java.util.function.Consumer;
  3.  
  4. class test<T> {
  5.  
  6.     public void foo(Consumer<Optional<T>> c) {
  7.         Optional<T> t = null;
  8.         c.accept(t); // compiles
  9.     }
  10.  
  11.     public void foo2(Consumer<? super Optional<?>> c) {
  12.         Optional<T> t = null;
  13.         //c.accept(t); // doesn't compile
  14.     }
  15.  
  16.     public static <T, S extends T> void foo3(Consumer<Optional<T>> c, test<S> test) {
  17.     	Optional<S> s = null;
  18.     	@SuppressWarnings("unchecked")  // Safe because of properties of Optional.
  19.     	Optional<T> t = (Optional<T>) (Optional<?>) s;
  20.     	c.accept(t);
  21.     }
  22.  
  23.     public static void main(String[] args) {
  24.         test<Integer> t = new test<>();
  25.         Consumer<Optional<Number>> crn = c -> {};
  26.         Consumer<Optional<Integer>> cri = c -> {};
  27.  
  28.         foo3(cri, t); // compiles
  29.         foo3(crn, t); // compiles
  30.     }
  31. }
Success #stdin #stdout 0.13s 4386816KB
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https://ideone.com/Jqi9y0
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
secret

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