明显的类型冲突，但编译

为什么下面的代码段会编译？ 不会扩展，所以我敢打赌一个肾脏，这不会编译。但事实确实如此。OtherInterfaceConcrete

public class Test {

    public static interface SomeInterface {}

    public static interface OtherInterface{}

    public static class Concrete implements SomeInterface {

       public <T extends Concrete> T getConcrete() {
            return null;
       }
    }

    public static void doStuff() {
        Concrete c = new Concrete();
        OtherInterface iCompile = c.getConcrete();
    }
}

另一方面，下一个代码段不会编译，这是我所期望的。

public class Test {

    public static interface SomeInterface {}

    public static class UnrelatedClass{}

    public static class Concrete implements SomeInterface {

       public <T extends Concrete> T getConcrete() {
            return null;
       }
    }

    public static void doStuff() {
        Concrete c = new Concrete();
        UnrelatedClass iCompile = c.getConcrete();
    }
}