How to convert reference types to primitive types and vice versa?

Conversion of reference types (wrappers) to primitive types (unboxing) and vice versa (autoboxing) occurs automatically in Java, but it can also be done explicitly.

Autoboxing: Automatic conversion of a primitive type to its corresponding reference type.

int primitiveInt = 10;
// Automatically converted to Integer
Integer wrapperInt = primitiveInt; 

Unboxing: Automatic conversion of a reference type to its corresponding primitive type.

Integer wrapperInteger = 20;
// Automatically converted to int
int primitiveInteger = wrapperInteger;

Explicit conversion:

Converting a reference type to a primitive: using methods like intValue(), doubleValue(), etc.

Integer wrapperInt = 30;
int primitiveInt = wrapperInt.intValue(); // explicit conversion

Double wrapperDouble = 40.5;
double primitiveDouble = wrapperDouble.doubleValue(); // explicit conversion

Converting a primitive type to a reference type: using wrapper class constructors or static methods valueOf(). The static method valueOf() is preferred as it can cache values.

int primitiveInt = 50;
Integer wrapperInt = new Integer(primitiveInt); // constructor (deprecated)

double primitiveDouble = 60.7;
Double wrapperDouble = Double.valueOf(primitiveDouble); // using valueOf()

Conversion table:

Primitive Type	Reference Type
boolean	Boolean
byte	Byte
short	Short
char	Character
int	Integer
long	Long
float	Float
double	Double