How to use wrapper classes with untyped collections

• Because untyped collections can't hold primitive types, you must use wrapper classes to store primitive types in them.
• To add a primitive type to an untyped collection:
• create an instance of the appropriate wrapper class
• pass the value you want it to hold to the constructor of that class
• You can assign the wrapper type to a primitive type variable without any explicit casting. To retrieve an element that holds a primitive type, cast the element to the wrapper type.

Wrapper classes for primitive types

Code that adds integers to an untyped array list

ArrayList numbers = new ArrayList();

numbers.add(new Integer(1));
numbers.add(new Integer(2));
numbers.add(new Integer(3));
Code that retrieves integers from the array list
for (int i = 0; i < numbers.size(); i++)
{
    int number = (Integer)numbers.get(i);
    System.out.println(number);
}

Resulting output