How to convert a number to binary or hex

Short answer

Integer has ready-made methods for binary, octal and hexadecimal notation:

void main() {
    int number = 255;
 
    IO.println(Integer.toBinaryString(number));
    IO.println(Integer.toOctalString(number));
    IO.println(Integer.toHexString(number));
}

Output:

11111111
377
ff

Any radix

Integer.toString(n, radix) converts to any base from 2 to 36:

void main() {
    IO.println(Integer.toString(255, 3));
    IO.println(Integer.toString(35, 36));
}

Output:

100110
z

Back to a number

parseInt() with a second argument reads a string in the given base:

void main() {
    IO.println(Integer.parseInt("1010", 2));
    IO.println(Integer.parseInt("ff", 16));
}

Output:

10
255

With leading zeros

toBinaryString() does not add leading zeros. Pad the string yourself, and for hexadecimal use HexFormat:

void main() {
    String bits = Integer.toBinaryString(5);
    IO.println("0".repeat(8 - bits.length()) + bits);
 
    IO.println(HexFormat.of().toHexDigits((byte) 10));
    IO.println(HexFormat.of().formatHex(new byte[] {1, 127, -1}));
}

Output:

00000101
0a
017fff

Common mistake

Being surprised by negative numbers. The methods show the internal representation — 32-bit two's complement:

void main() {
    IO.println(Integer.toBinaryString(-1));
    IO.println(Integer.toHexString(-1));
    IO.println(Integer.toString(-1, 2));
}

Output:

11111111111111111111111111111111
ffffffff
-1

If you need a minus sign, use Integer.toString(n, 2).

Thanks for reading!

Short answer

Any radix

Back to a number

With leading zeros

Common mistake

Functions used in this recipe

Thanks for reading!