Java Generic interface with List<T> not accepting object type

Question

I am trying to implement a system as follows:

DtoMapper: This is an interface which defines a contract any third party mappers should return objects as

    public interface DtoMapper<T> {

    /**
     * Converts list of T into FooResponse
     * @param List of T
     * @return FooResponse
     */
    FooResponse convertToFooResponse(final List<T> rewards);

FooMapper: implements DtoMapper passing a List of Bar as method argument, however the compiler does not like my override of the method implementation and is wanting the second implementation (bottom).

public final class FooMapper implements DtoMapper {


    @Override
    FooResponse convertToFooResponse(final List<Bar> listOfBars) {
        ... Logic
    }

     @Override
    public convertToFooResponse(final List listOfBars) {
        ... I dont want this
    }

How can I make my interface work with this requirement, so that in future another implementation of say public convertToFooResponse(final list<Snafu> listOfSnafus); ?

Can you show the declaration of FooMapper?

M A
– M A

2016-09-08 11:06:20 +00:00
Commented Sep 8, 2016 at 11:06 — M A
– M A, Commented Sep 8, 2016 at 11:06
Updated the class declaration for you

tomaytotomato
– tomaytotomato

2016-09-08 11:07:58 +00:00
Commented Sep 8, 2016 at 11:07 — tomaytotomato
– tomaytotomato, Commented Sep 8, 2016 at 11:07

Jose Ignacio Acin Pozo · Accepted Answer · 2016-09-08 11:07:00Z

5

You need to explicitely implement DtoMapper<Bar> instead of DtoMapper.

Example:

public interface DtoMapper<T> {

    /**
    * Converts list of T into FooResponse
    * @param List of T
    * @return FooResponse
    */
    FooResponse convertToFooResponse(final List<T> rewards);
}

public class FooMapperImplementation implements DtoMapper<Bar> {
    @Override
    public FooResponse convertToFooResponse(List<Bar> rewards) {
        return null;
    }
}

answered Sep 8, 2016 at 11:07

Jose Ignacio Acin Pozo

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Comments

Mureinik · Accepted Answer · 2016-09-08 11:08:38Z

3

You need to pass the generic specification when implementing the class:

public final class FooMapper implements DtoMapper<Bar> {
// Here -----------------------------------------^

    @Override
    FooResponse convertToFooResponse(final List<Bar> listOfBars) {
        ... Logic
    }

answered Sep 8, 2016 at 11:08

Mureinik

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2 Comments

Jose Ignacio Acin Pozo Over a year ago

This answer is not adding anything new not provided in stackoverflow.com/a/39389316/6783451 which was posted before yours.

Michaela Elschner Over a year ago

If think @JoseIgnacioAcinPozo is right. And he also added more information.

Ady Junior · Accepted Answer · 2016-09-08 11:13:28Z

1

You forgot the parameterized type

class FooResponse{}
class First{}
class Second{}

public interface DtoMapper<T> {
    FooResponse convertToFooResponse(final List<T> rewards);    
}

class FirstMapper implements DtoMapper<First> {
    @Override
    public FooResponse convertToFooResponse(List<First> list) {
        return null;
    }
}

class SecondMapper implements DtoMapper<Second> {
    @Override
    public FooResponse convertToFooResponse(List<Second> list) {
        return null;
    }
}

answered Sep 8, 2016 at 11:13

Ady Junior

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Comments

engtuncay · Accepted Answer · 2023-01-26 10:36:29Z

0

Before calling the method, you can create a new list with interface type.

List<InterfaceType> listWithInterfaceType = new ArrayList<>(listWithObjectType);

edited Jan 26, 2023 at 10:36

answered Jan 26, 2023 at 6:11

engtuncay

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