英文:
Why is java.util.Set not Assignable From java.lang.Iterable?
问题
当我调用Set.class.isAssignableFrom(Iterable.class)时，它返回false。
然而，在文档中，java.util.Set被列为java.lang.Iterable的子接口。因此我感到困惑。你甚至可以尝试在一行代码中测试：
System.out.println(Set.class.getName() + " is " + ((Set.class.isAssignableFrom(Iterable.class)) ? "" : "NOT ") + "assignable from " + Iterable.class.getName());
它会打印出java.util.Set is NOT assignable from java.lang.Iterable。
为什么会这样呢？
英文:
When I call Set.class.isAssignableFrom(Iterable.class), it returns false.
Nevertheless, in the docs, java.util.Set is listed as a subinterface of java.lang.Iterable. Hence my confusion. You can even try it out in a single line of code:
System.out.println(Set.class.getName() + " is " + ((Set.class.isAssignableFrom(Iterable.class)) ? "" : "NOT " ) + "assignable from " + Iterable.class.getName());
it prints java.util.Set is NOT assignable from java.lang.Iterable.
Why is that?
答案1
得分: 3
因为你错误地使用了 isAssignableFrom。
正如文档所述，isAssignableFrom(Class<?> cls) "确定由此Class对象表示的类或接口是否与指定的Class参数表示的类或接口相同，或者是指定的Class参数的超类或超接口"。所以 cls 应该是 Set.class，完整的语法是：
Iterable.class.isAssignableFrom(Set.class)。
...确实会返回 true。
英文:
That's because you're using isAssignableFrom wrong.
As the docs say, isAssignableFrom(Class<?> cls) "determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter". So cls would be Set.class, and the full syntax would be:
Iterable.class.isAssignableFrom(Set.class).
...which, indeed, returns true.
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