Wild card characters with super keyword

If we want to force the method to allow particuler type list or it’s super classes type list as parameter we have to use super keyword. See , below example.

public int size(List<? super X> arrayList) {
—-
}


1) If X is a class then above method is applicable for ArrayList of X type or its super classes .

2) If X is a interface then above method is applicable for ArrayList of X type or super classes of X implementation types.

3) With in the method we can add X type elements and ‘null’ only . See the below example.

import java.util.ArrayList;
import java.util.List;

public class Sample {
    public int size(List<? super String> arrayList) {
        arrayList.add("raj"); 
        return arrayList.size();
    }

    public static void main(String as[]) {
        List<String> names = new ArrayList<String>();
        List<Integer> age = new ArrayList<Integer>();
        names.add("sree");
        names.add("krish");
        System.out.println(new Sample().size(names));
    }
}