A parameterized bean type is considered assignable to a parameterized required type if they have identical raw type and for each parameter: * the required type parameter is an actual type, the bean type parameter is a type variable and the actual type is assignable to the upper bound, if any, of the type variable, or

From: "Laird Nelson" <ljnelson(a)gmail.com&gt; To: "Matej Novotny" <manovotn(a)redhat.com&gt; Sent: Sunday, April 26, 2020 10:52:57 PM Subject: Odd type assignability test Hello; I ran across this test during some code reading to better understand type assignability. It's in BeanTypeAssignabilityTest.java: @Test public <E> void testStringFooMatchesVariableFoo() throws Exception { Type stringFooType = new TypeLiteral<Foo<String>>() { }.getType(); Type variableFooType = new TypeLiteral<Foo<E>>() { }.getType(); Assert.assertTrue("Foo<String> should match Foo<E>", getRules().matches(stringFooType, variableFooType)); } Am I reading this right? Is this saying that a reference of type Foo<String> should be able to receive a Foo<E>, where E doesn't extend String? I understand that any method that declares a type variable E and returns a Foo<E> will happen to produce a compatible reference. That is: public <E> Foo<E> blatz() { /* ... */ } can be called like this: final Foo<String> foo = blatz(); // should work; E's upper bounds will be String here But in this test, E has no upper bounds, so how does it work? Thanks, Laird