Question

What will be equivalent of this in Java?

for (i = (sizeof(num)*8-1); i; i--)  

num is given number, not array. I want to reverse bits in integer.

Answer 1

Java does not have sizeof. Arrays have the length property, and many collections have size() and similar things like that, but a linguistic sizeof for any arbitrary object is both not supported and not needed.

Related questions

• Is there any sizeof-like method in Java?
• In Java, what is the best way to determine the size of an object?

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Getting bits of an integer in LSB-MSB order

To get the bits of an integer from its least significant bit to its most significant bit, you can do something like this:

    int num = 0xABCD1234;
    System.out.println(Integer.toBinaryString(num));
    for (int i = 0; i < Integer.SIZE; i++) {
        System.out.print((num >> i) & 1);
    }

This prints:

10101011110011010001001000110100    // MSB-LSB order from toBinaryString
00101100010010001011001111010101    // LSB-MSB order from the loop

So in this specific case, the sizeof * 8 translates to Integer.SIZE, "the number of bits used to represent an int value in two’s complement binary form". In Java, this is fixed at 32.

JLS 4.2.1 Integral types and values

For int, from -2147483648 to 2147483647, inclusive