Java Autoboxing and Unboxing

The autoboxing and unboxing Java features let you write cleaner and easier-to-read code by allowing you to use either primitive data types or their corresponding wrapper objects. Java then automatically makes the needed conversions in code at runtime.

	Conversion	Applied when
Autoboxing	Primitive → Wrapper	A primitive value is: Passed as a parameter to a method that expects an object of the corresponding wrapper class Assigned to a variable of the corresponding wrapper class.
Unboxing	Wrapper → Primitive	A wrapper object is: Passed as a parameter to a method that expects a value of the corresponding primitive type Assigned to a variable of the corresponding primitive type Used in expressions with operators

Conversion

Applied when

Autoboxing

Primitive → Wrapper

A primitive value is:

Passed as a parameter to a method that expects an object of the corresponding wrapper class
Assigned to a variable of the corresponding wrapper class.

Unboxing

Wrapper → Primitive

A wrapper object is:

Passed as a parameter to a method that expects a value of the corresponding primitive type
Assigned to a variable of the corresponding primitive type
Used in expressions with operators

Autoboxing and unboxing both work for all primitive data types, including char and boolean.


  // Example 1: Autoboxing by parameter passing
  List<Integer> list = new ArrayList<>();
  int i = 8; 
  list.add(i);      // converted to: list.add(Integer.valueOf(i));

  // Example 2: Unboxing by assignment
  i = list.get(0);  // converted to: i = list.get(0).intValue();

  // Example 3: Unboxing by using operators
  Integer a = new Integer(1);
  i = (a + 2);      // converted to: i = (a.intValue() + 2);

// Example 1: Autoboxing by parameter passing

List<Integer> list = new ArrayList<>();

int i = 8;

list.add(i); // converted to: list.add(Integer.valueOf(i));

// Example 2: Unboxing by assignment

i = list.get(0); // converted to: i = list.get(0).intValue();

// Example 3: Unboxing by using operators

Integer a = new Integer(1);

i = (a + 2); // converted to: i = (a.intValue() + 2);

Leave a Reply Cancel Reply