What are wrapper classes in Java?

A wrapper class in Java converts a primitive data type into class object.

Java is an object-oriented language that only supports pass by value. Therefore, wrapper class objects allow us to change the original passed value. These wrapper classes help with multithreading and synchronization because, in Java, multithreading only works with objects. Moreover, most collections (like Vector, LinkedList, etc.) work with objects.

Autoboxing

The automatic conversion of primitive data types into its wrapper class objects is known as autoboxing.

class Autoboxing {
    public static void main( String args[] ) {
     int a = 15; // Primitive data type
     Integer I = a; // Autoboxing will occur internally.
    }
}

Unboxing

The automatic conversion of wrapper class objects into its primitive data types is known as unboxing.

class Autoboxing {
    public static void main( String args[] ) {
      Integer a = new Integer(15); // Wrapper class object
      int I = a;// Unboxing will occur internally.
    }
}