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Weird java behavior with casts to primitive types
Why does this code in Java,
int i = (byte) + (char) - (int) + (long) - 1;
System.out.println(i);
prints 1? Why does it even compile?
Source: Java Code Geeks
Source: Tips4all, CCNA FINAL EXAM
What you are doing is combining type casts with unary operators.
ReplyDeleteSo let's see:
First, you have the value -1, which you cast to the type long.
Then, you perform the unary operation +, which doesn't change the value, so you still have (long) -1.
Then, you cast it to int, so we now have int -1. Then, you use unary operator -, so we have -(-1), which is 1.
Then you cast it to char, so we have char 1. Then, you use unary operator +, so you still have 1.
Finally, the value is cast to byte, so you have byte 1. And then it is once again (implicitly) cast to int.
The various (<type>) parts are just casting between various types. So what happens is, reading from the right, 1 -> -1 -> (long)-1 -> (int)-1 -> -(int)-1 = 1 -> (char)1) -> (byte)1 which then gets cast to an int during the assignment. At no point does the type cast result in effective change of the value, so the entire first line is equivalent to int i = 1;.
ReplyDeleteThis goes right to left. -1 gets cast to long. Then the + prefix is applied (which has no effect), and it's cast to int. Then the - gets applied (changing it to 1) and it gets cast to char. Lastly, the + prefix is applied (which still has no effect) and it's cast to byte.
ReplyDeletelets add parenthesis:
ReplyDeleteint i = ((byte) + ((char) - ((int) + ((long) (- 1)))));
System.out.println(i);
basically this is just a series of casts and unary operators (+ does nothing, - negates)
the full program flow is in luiscubal's answer