Generics allow our programs to adapt to different data type needs but one issue with them is that we cannot use primitive types (int, double, boolean, etc) as arguments to generic type parameters. For example, we cannot create a Box of integers this way:

Box<int> intBox = new Box<>(56);

Fortunately, Java provides wrapper classes to allow us to create objects of primitive types and use them as type parameters. We can now create a Box of integers this way:

Box<Integer> intBox = new Box<>(56);

In the example above, the Integer wrapper class is used in place of int to work as a type argument. Also, notice that we are able to pass 2 as the argument to the constructor and this is because of autoboxing.

Autoboxing allows wrapper classes to take primitive values and convert them to their corresponding wrapper object by automatically calling the valueOf() method. For example, the following statements are equivalent when creating a Box<Integer>:

Integer a = 56;  // Autoboxing, automatic call to `valueOf()`
Box<Integer> intBox1 = new Box<>(a);
Box<Integer> intBox2 = new Box<>(56);  // Autoboxing, automatic call to `valueOf()`
Box<Integer> intBox3 = new Box<>(Integer.valueOf(56));

We can also take the wrapper object and convert it back to its primitive value using one of the wrapper object’s Value() methods. This process is also automated for us and is known as unboxing. For example:

Integer a = 56;
int aPrimitive1 = a.intValue();  // Return primitive `int` value from `Integer` object
int aPrimitive2 = a;  // Unboxing, automatic call to `intValue()`