[FIXED] How to fix 'Unchecked cast from MyClass to T'

Issue

I have a method that works, but give me a warning, is there any solution to remove it, cleanly?

• In this method I call the method :
  <T extends SonarContainPaging> T getSonarObjectFromPage(String url, Map<String, Object> uriVariables, Class<T> klass, List<T> page)
  That return an object that extends SonarContainPaging.

• I try to add an object that extends SonarContainPaging to my list, but I get a warning.

• The SonarContainPaging object has a method canContinuePaging that takes a page integer and return a boolean.

The warning:

Type safety: Unchecked cast from SonarContainPaging to T

private <T extends SonarContainPaging> void getSonarListContainingPaging(String url, Map<String, Object> uriVariables, 
        Class<T> klass, List<T> list) {
    int page = 1;
    SonarContainPaging sonarObject = getSonarObjectFromPage(url, uriVariables, klass, page);
    page++;

    list.add((T)sonarObject); // Warning
    while (sonarObject.canContinueLooping(page)) {
        sonarObject = getSonarObjectFromPage(url, uriVariables, klass, page);
        page++;

        list.add((T) sonarObject); // Warning
    }
}

Any solution you can think of?

---

The solution given by @Sweeper is to change the type of sonarObject to T
The error I made, was assuming that a generic T object could not call method from its parent.

Solution

The solution is to use T as the type here and then you can remove your casts:

// before:
// SonarContainPaging sonarObject = getSonarObjectFromPage(url, uriVariables, klass, page);
// after:
T sonarObject = getSonarObjectFromPage(url, uriVariables, klass, page);

Since according to your comment, getSonarObjectFromPage returns T, where T is the class you pass it in:

<T extends SonarContainPaging> T getSonarObjectFromPage(String url, Map<String, Object> uriVariables, Class<T> klass, List<T> page)

In this case you passed the class klass, which is a Class<T>, so getSonarObjectFromPage will return a T as well.

Answered By - Sweeper

Answer Checked By - Timothy Miller (PHPFixing Admin)