Using eclipse 4.2 with Java 7 and trying to implement the following method of the List interface i got a warning.
public <T> T[] toArray(T[] a) {
return a;
}
The warning says :
The type parameter T is hiding the type T
Why ? How can i get rid of it ?
Answer
The List interface is also generic. Make sure that you are not also using T for the generic type in your class. Note that in http://docs.oracle.com/javase/6/docs/api/java/util/List.html, they use “E” for the class generic parameter and “T” for the toArray() generic parameter. This prevents the overlap.
public class MyList<T> implements List<T> {
// V1 (compiler warning)
public <T> T[] toArray(T[] array) {
// in this method T refers to the generic parameter of the generic method
// rather than to the generic parameter of the class. Thus we get a warning.
T variable = null; // refers to the element type of the array, which may not be the element type of MyList
}
// V2 (no warning)
public <T2> T2[] toArray(T2[] array) {
T variable = null; // refers to the element type of MyList
T2 variable2 = null; // refers to the element type of the array
}
}