实现泛型接口 为什么可以任意返回?

我也不知道为什么, 想问一下.
我的问题,记录
我需要看: https://docs.oracle.com/javase/tutorial/java/generics/index.html
找到了答案: https://www.liaoxuefeng.com/wiki/1252599548343744/1265104600263968 泛型的类型擦除.

这个造成了一个问题:
consume records from Kafka, got a ClassCastException

    private class KafkaMessage {}

    private class AvroGeneric {}

    class Record<K, V> {
        K k;
        V v;
    }

    interface DeSerialize<T> {
        T deserializer();
    }

    class AvroDeserializer implements DeSerialize {
        @Override
        public Object deserializer() {
            return new AvroGeneric();
        }
    }

    @Test
    public void testGenericDiff() {
        // KafkaMessage is what I want.
        Record<String, KafkaMessage> record = new Record<>();

        // consume from xxx, get a AvroGenricObject. 
        DeSerialize<KafkaMessage> deSerialize = new AvroDeserializer();
        record.v = deSerialize.deserializer();

        // this is the problem, a AvroGeneric is assigned to a KafkaMessage variable.
        KafkaMessage v = record.v;
        System.out.println(v);
    }