The "Java" basic data type and its conversion

Sort out the Java basic data types and the knowledge that the interview might involve.

		Number of bytes (byte)	Number of bits (bit)	Range of values
Integral type	Byte	1	8	-2^7 ~ 2^7-1
	Short	2	16	-2^15 ~ 2^15-1
	int*	4	32	-2^31 ~ 2^31-1
	Long	8	64	-2^63 ~ 2^63-1
Floating point Type	Float	4	32
	double*	8	64
Character type	Char	2	16	0~2^16-1
Boolean type	Boolean	1

The range of values for integral types:

The highest bit is the symbol, plus or minus each 2^ (bit-1) number, 0 is positive, so the positive range is 0~2^ (bit-1)-1, negative is -2^ (bit-1) ~-1

Range of values for floating-point types:

The range of float and double is determined by the number of digits of the exponent. Do not understand this, later review and then look.

Https://www.cnblogs.com/BradMiller/archive/2010/11/25/1887945.html, this is a good piece of writing.

1. Conversions between basic data types

Reference: https://www.cnblogs.com/liujinhong/p/6005714.html

Low Precision	→→ Automatic Conversion →→			High Precision
	Byte, char, short,int, long, float,double
	←← Cast ←←

Because the default integer data in Java uses int, the floating-point type uses double, so the writing specification:

byte a = 1;　　　 Auto Convert byte B = (byte) 128;　 Values out of range need to be cast long C = 10000000000L;　　　　　 Cast float d = 3.5f; Cast double e = 3.5;

When you perform a mathematical operation, the data type is converted to the largest form of data involved

int a = 2;byte b = 2;byte c = (byte) (a+b);d ouble d = 5;char ch = (char) (' a ' + 1);

Char type is automatically promoted to int

char a = 55;char B = ' a '; char C = (char) (a+b); char d = ' a ' + ' a '; System.out.println (a);//7system.out.println (b);//a

2. Wrapper classes for basic data types and their conversions

basic data type	boolean	char	byte	SHORT 	int	long	float	double
Packing class	Boolean	Character	Byte	Short	Integer	Long	Float	Double

Box packing and unpacking

Integer i = 10;　　　　　Boxing base type → wrapper type int n = i; Unboxing wrapper type → basic type

View the corresponding. class file to discover the method that the above code actually calls:

Integer i = integer.valueof (ten); int n = I.intvalue ();

The ① Integer ( pointing to Cache/Chang) and the new integer(pointing to the heap) are different when compared to the memory location.

When ②integer (non-new) is compared to each other, the value is within the Int value range, the result is true, the range is false

③int and integer/new integer comparisons, the result of the comparison must be true, since the integer will first be unboxing and int.

Note: Double comparison is different, all double comparisons are false

Details: https://www.cnblogs.com/dolphin0520/p/3780005.html

The "Java" basic data type and its conversion