CODEWITHSUNDEEP
javagenericsinterface
Aldo Bertero
Aldo Bertero

Reputation: 33

Compiler error using java generics with a List as a method parameter and throws generic Exception

I'm getting a Compiler error when using generics in my project. I generate a sample code:

My Bean Interface

package sample;

public interface MyBeanInterface {
  Long getId();
  String getName();
}

My Bean Concrete Class

package sample;

public class MyBean implements MyBeanInterface {
    private Long id;
    private String name;

    @Override
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    @Override
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

My Manager Interface

package sample;

import java.util.List;

public interface MyManagerInterface<T extends MyBeanInterface> {

    <EXCEPTION extends Exception> List<T> sortAll(List<T> array) throws EXCEPTION;

    List<T> sortAll2(List<T> array);

    <EXCEPTION extends Exception> List<T> sortAll3() throws EXCEPTION;

}

My Manager Concrete Class

package sample;

import java.io.IOException;
import java.util.List;

public class MyConcreteManager implements MyManagerInterface<MyBean> {

   @Override
   //this fails
   public List<MyBean> sortAll(List<MyBean> array) throws IOException {
       return null;
      }

    @Override
   //this works
    public List<MyBean> sortAll2(List<MyBean> array) {
        return null;
    }

    @Override
   //this works
    public List<MyBean> sortAll3() {
        return null;
    }

}

I tried using the method sortAll with no method parameters (sortAll()) in the interface and it compiles, using only the exception in the interface also works, but using both not.

Thanks.

Upvotes: 3

Views: 90

Answers (1)

Konstantin Yovkov
Konstantin Yovkov

Reputation: 62864

With regards to the sortAll(List<T> list) method, you have to do:

@Override
public <E extends Exception> List<T> sortAll(List<T> array) throws E {
    // TODO Auto-generated method stub
    return null;
}

and then, when invoking the method to explicitly set the methods type-parameter:

try {
    new MyConcreteManager().<IOException>sortAll(...);
} catch (IOException e) {

}

The sortAll3() implementation compiles fine, because in Java, when a method definition overrides another one, it is not allowed to throw additional checked exceptions, but it may throw fewer.

Upvotes: 2

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