Wrapper Classes

In Java, every primitive data type has a corresponding class which works like a wrapper. It provides a mechanism to wrap primitive data into an object. • All wrapper classes are final and present in java.lang package.

Mapping:

(Byte, Short, Integer, Long, Float, Double are subclasses of Number class).

Use of Wrapper Class

1. To represent primitive data as Objects (Reference Types).
2. To convert String primitives to actual primitives (Parsing).
3. Used in Collections which store only Objects.

AutoBoxing & Unboxing

1. AutoBoxing:

Automatic conversion of primitive type into its corresponding wrapper object. Integer i = 10; // AutoBoxed

2. Unboxing:

Automatic conversion of wrapper object into its corresponding primitive type. int j = i; // Unboxed

Parsing (String to Primitive)

Every wrapper class has a valid static method parseXxx(String s). • public static int parseInt(String s) • public static double parseDouble(String s) • public static boolean parseBoolean(String s) • Note: char cannot be parsed (Use charAt()).

NumberFormatException

Thrown when trying to convert a String with invalid format into a number. Example: Integer.parseInt("123a") throws NumberFormatException.