What are wrapper classes and why are they useful for ArrayLists? In your answer, include examples of autoboxing and unboxing.
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Introduction:
Wrapper classes are classes that provide a way to use primitive data types like int, boolean, etc. as objects. Those objects can be used with Java's Collection framework. It is useful for ArrayLists as they store only objects (not primitives). Autoboxing and unboxing are two features that automatically convert a primitive data type to its corresponding wrapper class (autoboxing) and the other way (unboxing).
Wrapper Classes:
A wrapper class is a class whose objects wrap or contain primitive data types. We can use a wrapper class to instantiate objects instead of using the int, double, float, char, etc. Wrapper classes are helpful for students learning Java since they embrace the object-oriented model 100%. Commonly used wrapper classes are Integer, Boolean, Long, Float, Double, etc. The wrapper classes allow the programmer to use primitive data types with the Java collections framework, which require objects.
Why are Wrapper Classes Useful for ArrayLists?
ArrayList is a collection class that can contain objects only. This means that an ArrayList can only contain objects and not primitive data types. Java provides wrapper classes to use primitive data types as objects. All the primitive data types such as int, short, byte, float, double, long, char, and boolean have their corresponding wrapper classes: Integer, Short, Byte, Float, Double, Long, Character, and Boolean respectively. Thus, it is possible to store primitive data type elements in an ArrayList.
Autoboxing and Unboxing:
Autoboxing is the process of automatically converting a primitive data type to its corresponding wrapper class. The compiler does this when a primitive type is used in a context where an object is expected. Unboxing is the opposite process when an object is automatically converted to a primitive data type. Both autoboxing and unboxing are useful for ArrayLists as they allow to store primitives in list objects.
Example 1: Autoboxing
// integer to Integer
int a = 20;
Integer b = a; // conversion of int to Integer is known as autoboxing
Example 2: Unboxing
// Integer to integer
Integer x = new Integer(10);
int y = x; //conversion of Integer to int is known as unboxing
In conclusion, wrapper classes are used to store primitive data types as objects. ArrayList, a collection class, cannot store primitives and hence they must be stored using wrapper classes. Autoboxing and unboxing are two processes used to convert primitives to wrapper classes and vice vera.They come in handy when using ArrayList.