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I understand what is a wrapper class, they primitive types (eg: int, double, etc) to objects of their respective class (eg: Integer, Double, etc).
But, why we need Wrapper classes, why we chose objects of their respective class.
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Why we need Wrapper Class. Wrapper Class will convert primitive data types into objects. The objects are necessary if we wish to modify the arguments passed into the method (because primitive types are passed by value). The classes in java.
For every primitive type in Java, there is a built-in object type called a wrapper class. For example, the wrapper class for int is called Integer; for double it is called Double.
A Wrapper Class is often used by Salesforce Developers for creating new objects within the purview of Apex code. It helps the users in consolidating a set of different fields (whether they belong to different objects or not) that are required the most during runtime.
Need of Wrapper Classes They convert primitive data types into objects. Objects are needed if we wish to modify the arguments passed into a method (because primitive types are passed by value). The classes in java. util package handles only objects and hence wrapper classes help in this case also.
Java is an object-oriented language and can view everything as an object. A simple file can be treated as an object , an address of a system can be seen as an object , an image can be treated as an object (with java.awt.Image) and a simple data type can be converted into an object (with wrapper classes). This tutorial discusses wrapper classes. Wrapper classes are used to convert any data type into an object.
The primitive data types are not objects; they do not belong to any class; they are defined in the language itself. Sometimes, it is required to convert data types into objects in Java language. For example, upto JDK1.4, the data structures accept only objects to store. A data type is to be converted into an object and then added to a Stack or Vector etc. For this conversion, the designers introduced wrapper classes.
What are Wrapper classes?
As the name says, a wrapper class wraps (encloses) around a data type and gives it an object appearance. Wherever, the data type is required as an object, this object can be used. Wrapper classes include methods to unwrap the object and give back the data type. It can be compared with a chocolate. The manufacturer wraps the chocolate with some foil or paper to prevent from pollution. The user takes the chocolate, removes and throws the wrapper and eats it.
Observe the following conversion.
int k = 100;
Integer it1 = new Integer(k);
The int data type k is converted into an object, it1 using Integer class. The it1 object can be used in Java programming wherever k is required an object.
The following code can be used to unwrap (getting back int from Integer object) the object it1.
int m = it1.intValue();
System.out.println(m*m); // prints 10000
intValue() is a method of Integer class that returns an int data type.
Importance of Wrapper classes
There are mainly two uses with wrapper classes.
1) To convert simple data types into objects, that is, to give object form to a data type; here constructors are used.
2) To convert strings into data types (known as parsing operations), here methods of type parseXXX() are used.
Features of the Java wrapper Classes.
1) Wrapper classes convert numeric strings into numeric values.
2) The way to store primitive data in an object.
3) The valueOf() method is available in all wrapper classes except Character
4) All wrapper classes have typeValue() method. This method returns the value of the object as its primitive type.
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