Java中整数到字节的转换

Question

Referring to page number 79 of " Java The complete Reference" 7th edition by Herbert Schildt. The author says : " If the integer's value is larger than the range of a byte, it will be reduced modulo (the remainder of an integer division by the) byte's range".

The range of byte in java is -128 to 127. So the maximum value that fits in a byte is 128. If an integer value is assigned to a byte as shown below :

int i = 257;
byte b;
b = (byte) i;

Since 257 crosses the range 127, 257 % 127 = 3 should be stored in 'b'. But am getting the output as 1 instead of 3. Where have I gone wrong in understanding the concept?

Answer 1

Just consider the binary representation of the numbers :

257 is represented in binary as 00000000 00000000 00000001 00000001

When you cast this 32 bits int to an 8 bits byte , you keep only the lowest 8 bits :

00000001

which is 1

Answer 2

257 = 00000000 000000000 00000001 00000001 in bits and a byte is made up of 8 bits only...

As a result only the lower 8 bits are stored and 1 is the output.