wildcard

public class GenericsInJava
{
static void processElements(ArrayList<? extends Number> a)
{
for (Object element : a)
{
System.out.println(element);
}
}

public static void main(String[] args)
{
//ArrayList Containing Integers

ArrayList<Integer> a1 = new ArrayList<>();

a1.add(10);

a1.add(20);

a1.add(30);

processElements(a1);

//Arraylist containing Doubles

ArrayList<Double> a2 = new ArrayList<>();

a2.add(21.35);

a2.add(56.47);

a2.add(78.12);

processElements(a2);

//Arraylist containing Strings

ArrayList<String> a3 = new ArrayList<>();

a3.add("One");

a3.add("Two");

a3.add("Three");

//This will not work

processElements(a3);     //Compile time error
}
}