How to use wrapper classes with untyped collections

Wrapper classes for primitive types:

Primitive type Wrapper class
byte Byte
short Short
int Interger
long Long
float Float
double Double
char Char
boolean Boolean

Example 1: Code that adds integers to an untyped array list:

ArrayList number = new ArrayList();
nubers.add(new Integer(1));
nubers.add(new Integer(2));
nubers.add(new Integer(3));

Example 2: Code that retrieves intergers from the array list:

for (int i = 0; numbers.size(); i++)
{
int number = (Integer)numbers.get(i);
System.out.pringln(number);
}

Description:

  • Because untyped collections hold elements of thpe Object, they can't hold primitive types. As a result you must use wrapper claases to store primitive types in a collection.
  • To add a primitive type to an untyped collectio, create an instance of the appropriate wrapper class and pass the value you want it to hold to the construtor of that class.
  • To retrieve an element that holds a primitive type, cast the element to the wrapper type.