int number = 0xFF；
Literal means without saving the variables in the program, can be directly expressed as a specific number or value strings.
0xFF is an integer literals, the default type is integer literals int.
We know that in Java, int is a 4-byte (32-bit) of the basic data types.
So 0xFF actually complete wording is 0x000000FF.
4 may represent a binary hexadecimal, then 0x000000FF converted to binary wording is:
0000 0000 0000 0000 0000 0000 1111 1111
Bitwise:
~number
= ~0xFF
= ~0x000000FF
= 0xFFFFFF00【H】 = 1111 1111 1111 1111 1111 1111 0000 0000【B】;
The first is the sign bit, 1 indicates a negative number, so there should be a conversion , the conversion from a negative form to complement the original code, in order to obtain real value it wants to express.
Converted from complement to the original code, obtained by subtracting 1 to the inverted and inverted to obtain the original code.
The first step, the least significant bit minus 1:
. 1 1,111,111,111,111,111,111 complement 1111 0000 [0000] --1 = . 1 1,111,111,111,111,111,111 code 1110111111111 [trans]
The second step, in addition to the sign bit, invert:
1 0,000,000,000,000,000,000 0001 0000 0000] [original code
After obtaining the original code, its value calculation part to give: 100,000,000 [B] = 2 . 8 [Q] = [Q] 256
Plus sign bit , the outcome is: -256
Therefore, the hexadecimal number 0xFF corresponding decimal number is negated after -256.
In summary, here are three related to knowledge.
First, in Java, the default type is integer literals int, it is composed by a 32bit;
Second, bitwise representation of a binary number ~ bitwise, i.e. 0 to 1, a 1 to a 0;
Second, in a computer system, there is the sign bit numeric code data is represented in the form of complement and storage. Complement itself it is positive; a negative complement code is converted to the original code, before the least significant digit by 1, and then everybody except the sign bit inverted, the original code is finally obtained.