Java program to illustrate Wrapper class?

Answer 1

java uses simple or primitive data types, such as int, char and Boolean etc. These data types are not part of the object hierarchy. They are passed by value to methods and cannot be directly passed by reference. However, at times there is a need to create an object representation of these simple data types. To address this need, Java provides classes that correspond to each of these simple types. These classes encapsulate, or wrap, the simple data type within a class. Thus, they are commonly referred to as wrapper classes.

Wrapper classes corresponding to respective simple data types are as given in table below.

Primitive Data Types

Wrapper class

byte

Byte

short

Short

int

Integer

long

Long

char

Character

float

Float

double

Double

boolean

Boolean

void

Void

eg

Say supposing there is a requirement to store only the

object in an array A.The Primitive types cannot be stored in

the same array as the array can accommodate only Objects

here is where Wrapper Class come into picture.ie, we create

wrapper for the primitive types.One such example is as below

Ex:int i;

Wrapper class for the primitive type(int) is created as below:

Integer i = new Integer();

Answer 2

The wrapper classes in the Java API serve two primary purposes:

• To provide a mechanism to "wrap" primitive values in an object so that the primitives can be included in activities reserved for objects, like being added to Collections, or returned from a method with an object return value.

• To provide an assortment of utility functions for primitives. Most of these functions are related to various conversions: converting primitives to and from String objects, and converting primitives and String objects to and from different bases (or radix), such as binary, octal, and hexadecimal.

An Overview of the Wrapper Classes

There is a wrapper class for every primitive in Java. For instance, the wrapper class for int is Integer, the class for float is Float, and so on. Remember that the primitive name is simply the lowercase name of the wrapper except for char, which maps to Character, and int, which maps to Integer.

The Wrapper classes for each of the primitive types is as follows:

1. boolean - Boolean

2. byte - Byte

3. char - Character

4. double - Double

5. float - Float

6. int - Integer

7. long - Long

8. short - Short

A point to note here is that, the wrapper classes for numeric primitives have the capability to convert any valid number in string format into its corresponding primitive object. For ex: "10" can be converted into an Integer by using the below line

Integer intVal = new Integer("10");