边界不匹配：类型A不是边界参数的有效替代品 <T extends Entity> 类型为TestService <T>

Question

Im getting this exception when compiling MyService. What is the issue in the generics definition here?

public interface Entity extends Serializable{

    public <T extends Serializable> T getId();

}

public  class A  implements Entity {
... some code
}



public abstract class TestService<T extends Entity> implements Serializable {
...some code
}

public class MyService extends TestService<A> {
...some code
}

Answer 1

The error simply tells that the type parameter T you are using here public abstract class TestService<T extends Entity> implements Serializable { is a bound parameter extending Entity .

Whereas, here public class MyService extends TestService<A> { , you are specifying an unbound parameter A .

I am not sure whether it has to do anything with the Java version 5 onwards, you can refer this Type Erasure