What is a wrapper class

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What is a wrapper class  How are such classes useful

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a wrapper is class which is used to communicate between two different application between different platform

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a wrapper class is usually a class that has an object as a private property  the wrapper implements that private object s API and so it can be passed as an argument where the private object would      say you have a collection  and you want to use some sort of translation when objects are added to it - you write a wrapper class that has all the collection s methods  when add   is called  the wrapper translate the arguments instead of just passing them into the private collection       the wrapper can be used anyplace a collection can be used  and the private object can still have other objects referring to it and reading it

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In general  a wrapper class is any class which  wraps  or  encapsulates  the functionality of another class or component   These are useful by providing a level of abstraction from the implementation of the underlying class or component  for example  wrapper classes that wrap COM components can manage the process of invoking the COM component without bothering the calling code with it   They can also simplify the use of the underlying object by reducing the number interface points involved  frequently  this makes for more secure use of underlying components

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Wrapper class is a wrapper around a primitive data type  It represents primitive data types in their corresponding class instances e g  a boolean data type can be represented as a Boolean class instance  All of the primitive wrapper classes in Java are immutable i e  once assigned a value to a wrapper class instance cannot be changed further

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Just what it sounds like  a class that  quot wraps quot  the functionality of another class or API in a simpler or merely different API  See  Adapter pattern  Facade pattern

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To make a wrapper class well being is not a easy job  To understand a wrapper class how it is designed by some others is also not a easy job  Because it is idea  not code  Only when you understand the idea  you can understand wrapper

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There are several design patterns that can be called wrapper classes   See my answer to  How do the Proxy  Decorator  Adaptor  and Bridge Patterns differ

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A wrapper class is a class that serves the sole purpose of holding something and adding some functionality to it  In Java since the primitives  like ints floats chars     are not objects so if you want to treat them like one then you have to use a wrapper class  Suppose you want to create a Vector of ints  the problem is a Vector only holds Objects not primitives  So what you will do is put all the ints in an Integer wrapper and use that  Example   int number   5  Integer numberWrapped   new Integer number     now you have the int in an object    and this is how to access the int value that is being wrapped  int again   numberWrapped intValue

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Wrapper class is a class that wrap the another class and provide the abstraction between client and the original class being wrapped

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A wrapper class is a class that  wraps  around something else  just like its name   The more formal definition of it would be a class that implements the Adapter Pattern   This allows you to modify one set of APIs into a more usable  readable form   For example  in C   if you want to use the native Windows API  it helps to wrap it into a class that conforms to the  NET design guidelines

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Wrapper classes came in to existence to fulfill a basic need of programmers - i e  to use primitive values wherever only Objects are allowed  As their name suggests wrapper classes wrap around a primitive value and hold the value in an Object  So  all those places where primitives were not allowed - such as generics  hashmap-keys  Arraylists etc - programmers now have an option of providing these primitive values as their corresponding wrapper types   In addition these wrapper types have a number of utility methods for converting from primitive type to corresponding wrapper types and back  and also from Strings to wrapper types and back   I have written a detailed article on wrapper classes in a my blog which explains the concept of wrapper types in depth - http   www javabrahman com corejava java-wrapper-classes-tutorial-with-examples    Disclosure - This blog is owned by me

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It might also be valuable to note that in some environments  much of what wrapper classes might do is being replaced by aspects   EDIT   In general a wrapper is going to expand on what the wrappee does  without being concerned about the implementation of the wrappee  otherwise there s no point of wrapping versus extending the wrapped class  A typical example is to add timing information or logging functionality around some other service interface  as opposed to adding it to every implementation of that interface     This then ends up being a typical example for Aspect programming   Rather than going through an interface function by function and adding boilerplate logging  in aspect programming you define a pointcut  which is a kind of regular expression for methods  and then declare methods that you want to have executed before  after or around all methods matching the pointcut   Its probably fair to say that aspect programming is a kind of use of the Decorator pattern  which wrapper classes can also be used for  but that both technologies have other uses

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Wrapper classes provide a way to use primitive types as objects  For each primitive   we have a wrapper class such as    int Integer byte Byte    Integer and Byte are the wrapper classes of primitive int and byte   There are times restrictions when you need to use the primitives as objects so wrapper classes provide a mechanism called as boxing unboxing    Concept can be well understood by the following example as   double d   135 0 d  Double doubleWrapper   new Double d    int integerValue   doubleWrapper intValue    byte byteValue   doubleWrapper byteValue    string stringValue   doubleWrapper stringValue      so this is the way   we can use wrapper class type to convert into other primitive types as well  This type of conversion is used when you need to convert a primitive type to object and use them to get other primitives as well Though for this approach   you need to write a big code   However  the same can be achieved with the simple casting technique as  code snippet can be achieved  as below   double d   135 0  int integerValue    int  d     Though double value is explicitly converted to integer value also called as downcasting

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A wrapper class is a class that is used to wrap another class to add a layer of indirection and abstraction between the client and the original class being wrapped

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A wrapper class doesn t necessarily need to wrap another class  It might be a API class wrapping functionality in e g  a dll file   For example it might be very useful to create a dll wrapper class  which takes care of all dll initialization and cleanup and create class methods that wrap function pointers created from e g  GetProcAddress     Cheers

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I currently used a wrapper class for my project and the main benefits I get  just a single benefit to widen the topic explanation    Exception handling  My main class  that another class wraps  has methods that are throwing exceptions if occurs any  so I created a wrapper class that handles the exceptions and logs them immediately  So  in my main scope  there is no exception handling  I just call a method and do something   Easy Usage  I can easily initiate the object  Normally initiating phase is constructed of a lot of steps   Code Readability  When another programmer opens my code  the code will seem very clear and easy to manipulate   Hiding the Details  If you are generating a class that another programmer is going to use  then you can wrap the details like  error handling  exception handling  logging messages and etc     so that the programmer will not be have to handle the chaos  just simply uses the methods

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Java programming provides wrapper class for each primitive data types  to convert a primitive data types to correspond object of wrapper class

[design-patterns] What is a wrapper class?

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