-128 as binary literal in Java

Question

Based on the fact that a byte type in java is a signed 8 bit two\'s complement integer, why doesn\'t the second way of declaring a byte work?

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Answer 1

Actually, as mentioned by Eng Fouad, 0b10000000 is an integer literal. Integer literals create an int value, the size of which in Java is 32-bit.The byte data type is an 8-bit signed two's complement integer.

So assigning the integer literal to a byte type would not work. To create a conversion between two incompatible types, one must use a cast.

 b = (byte)0b10000000;        // (This is narrowing conversion)

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_{Also, the signed 2's complement representation of -128 is 110000000. But, the MSB 's 1 can be discarded(represents negative sign bit) and hence 10000000 is acceptable as 2's complement representation of -128.}

Answer 2

0b10000000 is an int literal (= 0b00000000000000000000000010000000) which equals to +128. byte holds 8 bits and cannot represent +128. However, you can achieve this as follows:

byte notok = (byte) 0b10000000;