Reference types in Java - ilya-khadykin/notes-outdated GitHub Wiki

There is actually no such thing as an object variable, there is only an object reference variable.

Wrapper classes

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

int primitive = 0;

Integer reference = Integer.valueOf(primitive);
int backToPrimitive = reference.intValue();

boxing

Integer reference = Integer.valueOf(primitive);

unboxing

int backToPrimitive = reference.intValue();

Implicit conversion

Integer a = 1;
int b = a;

Integer c = 10;
Integer d = 10;
Integer e = c + d; // much slower than primitives due to overhead of boxing/unboxing

Conversion to/from String

long fromString = Long.parseLong("12345"); // static method

String fromLong = Long.toString(12345); // static method

String concatenation = "area" + 51; // automatic conversion

Useful methods

short maxShortValue = Short.MAX_VALUE;

int bitCount = Integer.bitCount(123);

boolean isLetter = Character.isLetter('a');

float floatInfinity = Float.POSITIVE_INFINITY;

double doubleNaN = Double.NaN;

boolean isNaN = Double.isNaN(doubleNaN);