(Java) Specify number of bits (length) when converting binary number to string?

Question

I\'m trying to store a number as a binary string in an array but I need to specify how many bits to store it as.

For example, if I need to store 0 with two bits I ne

Answer 1

Try this:

String binaryString = String.format("%"+Integer.toString(size)+"s",Integer.toBinaryString(19)).replace(" ","0");

where size can be any number the user wants

Answer 2

Here's a simple solution for int values; it should be obvious how to extend it to e.g. byte, etc.

public static String bitString(int i, int len) {
    len = Math.min(32, Math.max(len, 1));
    char[] cs = new char[len];
    for (int j = len - 1, b = 1; 0 <= j; --j, b <<= 1) {
        cs[j] = ((i & b) == 0) ? '0' : '1';
    }
    return new String(cs);
}

Here is the output from a set of sample test cases:

  0   1                                0                                0
  0  -1                                0                                0
  0  40 00000000000000000000000000000000 00000000000000000000000000000000
 13   1                                1                                1
 13   2                               01                               01
 13   3                              101                              101
 13   4                             1101                             1101
 13   5                            01101                            01101
-13   1                                1                                1
-13   2                               11                               11
-13   3                              011                              011
-13   4                             0011                             0011
-13   5                            10011                            10011
-13  -1                                1                                1
-13  40 11111111111111111111111111110011 11111111111111111111111111110011

Of course, you're on your own to make the length parameter adequate to represent the entire value.