Question

As you know, the binary literal is a new feature that is introduced in Java 7:

int x = 0b1011;
System.out.println(x); // prints 11 as expected

But, when I tried to get the maximum number from the literal binary I got -1!!!

int x = 0b11111111111111111111111111111111;
System.out.println(x); // prints -1 !!!

---

Further Details:

System.out.println(Integer.MAX_VALUE);
System.out.println(0b1111111111111111111111111111111); // 31 bits

/* Both print 2147483647 */

/************************************************************************************/

System.out.println(Integer.MIN_VALUE);
System.out.println(0b10000000000000000000000000000000); // 32 bits (increment by 1)

/* Both print -2147483648 */

/************************************************************************************/

// And if you keep increasing the binary literal, its actual value
// will be decreased until you reach the maximum binary literal and
// its actual value will be -1.

System.out.println(0b11111111111111111111111111111111); // 32 bits

/* Prints -1 */

As you can see, the actual value of the literal binary (while the increment) jumps over from the maximum value of int to the minimum one and then keep decreasing till it reaches -1 which is the maximum value of the literal binary.

Is this a bug? or does it have something to do with signed/unsigned numbers?

Answer 1

You’re using a signed integer. Bit 32 (the “first” one from the left) is the sign bit. It being 1 means it is a negative number, and 0 means positive. Two’s complement is then performed to give the value of -1. Read about that here:

http://tfinley.net/notes/cps104/twoscomp.html