[英]Incompatible types: java.lang.Class<capture#1 of ?> cannot be converted to
I have a rather weird problem with generics, where Java reports a compilation error.我对泛型有一个相当奇怪的问题,Java 报告编译错误。
Background: I am creating my own Kafka client wrapper.背景:我正在创建自己的 Kafka 客户端包装器。 One thing I need to support is for users of lib to supply their own key serializer class and value serializer class.我需要支持的一件事是让 lib 用户提供他们自己的关键序列化器类和值序列化器类。
Let's say that I have:假设我有:
import org.apache.kafka.common.serialization.Serializer;
// ...
private Class<? extends Serializer<?>> keySerializerClass;
private Class<? extends Serializer<?>> valueSerializerClass;
// ...
public Builder<K, V> serializeWith(Class<? extends Serializer<?>> keySerializerClass,
Class<? extends Serializer<?>> valueSerializerClass)
{
this.keySerializerClass = keySerializerClass;
this.valueSerializerClass = valueSerializerClass;
return this;
}
Now, at the call-site, if I do:现在,在呼叫站点,如果我这样做:
import org.apache.kafka.common.serialization.StringSerializer;
import io.confluent.kafka.serializers.KafkaAvroSerializer;
// ...
builder.serializeWith(StringSerializer.class, KafkaAvroSerializer.class);
It works perfectly.它完美地工作。 However, if I attempt :但是,如果我尝试:
import org.apache.kafka.common.serialization.StringSerializer;
import io.confluent.kafka.serializers.protobuf.KafkaProtobufSerializer;
// ...
builder.serializeWith(StringSerializer.class, KafkaProtobufSerializer.class);
It screams with a compilation error:它尖叫着编译错误:
java: incompatible types: java.lang.Class<capture#1 of ?> cannot be converted to java.lang.Class<? extends org.apache.kafka.common.serialization.Serializer<?>>
which does not make any sense to me.这对我没有任何意义。 After all, KafkaProtobufSerializer
conforms the <? extends Serializer<?>>
毕竟, KafkaProtobufSerializer
符合<? extends Serializer<?>>
<? extends Serializer<?>>
bounded generic: <? extends Serializer<?>>
有界泛型:
public class KafkaProtobufSerializer<T extends Message> extends AbstractKafkaProtobufSerializer<T> implements Serializer<T> {
Please tell me that I overlooked some silliness :)请告诉我,我忽略了一些愚蠢:)
There are a few options you could try, if you have the ability to modify your Builder class:如果您有能力修改 Builder 类,则可以尝试以下几个选项:
public Builder<K, V> serializeWith(Class<? extends Serializer<K>> keySerializerClass,
Class<? extends Serializer<V>> valueSerializerClass)
{
this.keySerializerClass = keySerializerClass;
this.valueSerializerClass = valueSerializerClass;
return this;
}
or removing the ?或删除? from Serializer:来自序列化程序:
public Builder<K, V> serializeWith(Class<? extends Serializer> keySerializerClass,
Class<? extends Serializer> valueSerializerClass)
{
this.keySerializerClass = keySerializerClass;
this.valueSerializerClass = valueSerializerClass;
return this;
}
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