Reputation: 1533

Converting integer variable to byte variable

Hello i'm learning java programming and i just had task in my book which says to convert int varible to byte variable

byte b;
int i=257;

And when i convert int to b

b=(byte) i;

Output is 1 ? How it can be one when value of byte variable goes from -128 to 127 In my book they say byte variable have range of validity to 256 ?

Upvotes: 3

Answers (6)

T.J. Crowder

Reputation: 1074276

The key here is to look at the bits.

int i = 257 gives us this set of bits (leaving off leading zeros):

b100000001

That value requires nine bits to hold (int has 32, so plenty of room). When you do b = (byte)i, it's a truncating cast. That means only what can be held by the byte (eight bits) is copied to it. So that gives us the lower eight bits:

b00000001

...which is the value 1.

Upvotes: 2

Linga

Reputation: 10553

Because it can store any number from -128 to 127. A byte is always signed in Java. You may get its unsigned value by binary-anding it with 0xFF.

Example:

int i = 234;
byte b = (byte) i;
System.out.println(b); // -22
int i2 = b & 0xFF;
System.out.println(i2); // 234

Upvotes: 2

Eng.Fouad

Reputation: 117587

257 == 00000000000000000000000100000001 (as integer which holds 32 bits)
  1 ==                         00000001 (byte holds only 8 bits)

Upvotes: 6

christopher

Reputation: 27346

The range of 256 is because it can store any number from -128 all the way to 127. The difference between these two numbers is 256. The value of 1 has occurred thanks to overflow, where you've attempted to store a value that can not be accurately represented with 7 bits and 1 sign bit.

Upvotes: 1