3*012 = 30 and not 36. Why is that?

Question

I am confused why this is and I cannot seem to find an answer why. This is from the assignment:

x=1, y=2, z=3;

z=(int)(x/y*3.0+z*012);

System.out.printf("%d %d %d", x, y, z);

Answer is :

1 2 30; << from eclipse

How I arrived here:

(1/2) = 0 * 3.0 = 0 + (z*012)= 30. I wanted to say 36 but I guess it is 30 according to the IDE.

Answer 1

012 is octal number not decimal which decimal value is 10.

z=(int)(x/y*3.0+z*012);

is equals -

z=(int)(1/2*3.0+3*10);

• For reference

Numeric starts with 0 is octal number.
Numeric starts with 0x is hexadecimal number.
Numeric starts with 0b or OB is binary number.(Since Java edition 7 - Binary Literals)

Answer 2

In Java and several other languages, an integer literal beginning with 0 is interpreted as an octal (base 8) quantity. Here 012 is an octal number which has a decimal value f 10

So your multiplication will come like

z = (int) (1/2 * 3.0 + 3 * 10);

From JLS

An octal numeral consists of an ASCII digit 0 followed by one or more of the ASCII digits 0 through 7 interspersed with underscores, and can represent a positive, zero, or negative integer.

Answer 3

012 is an octal, because it starts with 0:

012 = (0 * 8^2) + (1 * 8^1) + (2) = 10

Therefore:

012 * 3 = 10 * 3 = 30

Notes:

• Remember that an octal is a number in base 8 (decimal is base 10), so it can't have digits larger or equal to 8.
• Similarly, hexadecimal numbers starts with 0x, for example: 0x12 = 1*16 + 2 = 18

Answer 4

See the JLS:

An octal numeral consists of an ASCII digit 0 followed by one or more of the ASCII digits 0 through 7 interspersed with underscores, and can represent a positive, zero, or negative integer.

So,

012 = 0 * 8² + 1 * 8¹ + 2 * 8⁰ = 10

In Java 7, you can use underscores in numeric literals which might help you interrupting the value.