A brief introduction to automatic conversion of java basic types

The specific automatic promotion types are as shown in the picture above. Among them, the conversion of long->float made me feel a little problematic at first, because long is 64-bit, but float is 32-bit.

So to find the answer, refer to the murder case caused by the automatic conversion of long to float in Java in the blog.

Reason

First of all, you need to know that the range of numbers that float can represent is larger than that of long. So it is conceivable that a long type number can be converted to float type.

　 Long type, the value range is -9 223 372 036 854 775 808 ~ 9 223 372 036 854 775 807 (-2⁶³ ~ 2⁶³ -1)

　 Float type, the value range is 2^(-149) ---> (2-2^(-23))*2^127, which is Float.MIN_VALUE and Float.MAX_VALUE

Any long type number can be represented using the float type representation method. However, since float has precision limitations, the precision may be lost during the conversion process,

such as 3111111111111111L ---->3.1111111E15---->3111111100465152, the precision is lost after conversion

Secondly You need to know how the 32 bits of float represent decimals (I learned it in the computer composition principles course at the university, but forgot it. I will study it now and hope I can remember it).

float memory storage principle

http://steve.hollasch.net/cgindex/coding/ieeefloat.html (IEEE754 standard)

(1) In decimal system, 123.456 can be expressed as 1.23456 × 10 ² , in binary, 10100.110 can be represented as 1.0100110 × 2⁴

(2) Floating point numbers have precision, and numbers exceeding the precision cannot be represented. For example, 0.0000000000000001 is accurate to x digits after the decimal point.

(3) IEEE floating point numbers have three parts: sign bit (S), exponent bit (E), and tail (M). Any number can be expressed in binary as S*1.M*2^E

表示形式如下:
Single:

(4) Summary: The representation range of float is

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