Cfrtjryk

I have written a simple method which returns the boolean value.

private boolean isActionAvailable(Collection<StudentConfiguration> studentConfigs){

       if(studentConfigs != null)

        {

            studentConfigs.forEach(studentConfig -> {

                if(studentConfig.action() == null || !studentConfig.action().equals(Action.DELETE)) {

                    return true;

                }

            });

        }

        return false;

    }

The method is throwing the following exception .

error: incompatible types: unexpected return value

            studentConfigs.forEach(studentConfig -> 

What's the problem with my code?

The lambda expression passed to forEach shouldn't have a return value.

It looks like you want to return true if any of the elements of the input Collection satisfies a condition:

private boolean isActionAvailable(Collection<StudentConfiguration> studentConfigs){

    if(studentConfigs != null) {

        if (studentConfigs.stream().anyMatch(sc -> sc.action() == null || !sc.action().equals(Action.DELETE))) {

            return true;

        }

    }

    return false;

}

As Holger suggested, this can be reduced to a single statement:

return studentConfigs != null && studentConfigs.stream().anyMatch(sc -> sc.action() == null || !sc.action().equals(Action.DELETE));

or

return studentConfigs != null ? studentConfigs.stream().anyMatch(sc -> sc.action() == null || !sc.action().equals(Action.DELETE)) : false;

Alternatively with Java9 and above you can use Stream.ofNullable and update as:

private boolean isActionAvailable(Collection<StudentConfiguration> studentConfigs) {

    return Stream.ofNullable(studentConfigs)

            .flatMap(Collection::stream)

            .anyMatch(studentConfig -> studentConfig.action() == null || !studentConfig.action().equals(Action.DELETE));

}

I don't recommend you use Stream API here. Look at how clear and simple the foreach version is:

private boolean isActionAvailable(Collection<StudentConfiguration> studentConfigurations) {

    if(studentConfigurations == null) {

        return false;

    }



    for (StudentConfiguration configuration : studentConfigurations) {

        if (!Action.DELETE.equals(configuration.action())) {

            return true;

        }

    }



    return false;

}

Otherwise, if you are a fanatic guy,

private boolean isActionAvailable(Collection<StudentConfiguration> configs) {

    return configs != null &&

           configs.stream()

                  .map(StudentConfiguration::action)

                  .anyMatch(Predicate.isEqual​(Action.DELETE).negate()));

}

The return statement in your lambda will terminate that lambda, not the isActionAvailable() method. Therefore, the inferred type of the lambda is now wrong, because forEach expects a Consumer.

See the other answers for how to solve that problem.

This is signature of forEach() method forEach(Consumer<? super T> action) .

It takes reference of Consumer interface which has method void accept(T t).
In your code you are overriding accept() and returning a value which is not valid as accept() has void return type.

Therefore it is showing error

 error: incompatible types: unexpected return value

            studentConfigs.forEach(studentConfig ->