Java: How to output all possible binary combinations (256 different sequences)?

Question

I need to create a function that outputs all possible binary combinations (2^8 == 256 different sequences of 8 bits.). I'm really stumped on this. I have to do it with nested loops, and am not sure how to go about it. Below is what I tried so far. I was told that I could write this program using 8 nested loops, each one going from 0 to 1; Also, I could try to do this with bit manipulation operators.

Although what I have below is obviously wrong, I tried my best to show that I at least tried this. I also need to put new line's after each closing bracket, to separate the output.

The output should look like this:

00000000

00000001

00000010

00000011

00000100

...

11111110

11111111

public static void outputBinary(){

int[][][][][][][][] num = new int[2][2][2][2][2][2][2][2];

    for (int i = 0; i < 2; i++){

    for (int j = 0; j < 2; j++){

    for (int k = 0; k < 2; k++){

    for (int l = 0; l < 2; l++){

    for (int m = 0; m < 2; m++){

    for (int n = 0; n < 2; n++){

    for (int o = 0; o < 2; o++){

    for (int p = 0; p < 2; p++){

        System.out.print(num[i][j][k][l][m][n][o][p]);

    } }}}}}}}

}

Thanks for looking.

Solution 1

No need for the array. Here is a slight modification to your code that will output all the permutations.

for (int i = 0; i < 2; i++){
  for (int j = 0; j < 2; j++){
    for (int k = 0; k < 2; k++){
      for (int l = 0; l < 2; l++){
        for (int m = 0; m < 2; m++){
          for (int n = 0; n < 2; n++){
            for (int o = 0; o < 2; o++){
              for (int p = 0; p < 2; p++){
                System.out.println("" + i + j + k + l + m + n + o + p);
              }
            }
          }
        }
      }
    }
  }
}

Do you have to use nested loops? Because this is trivially easy when you simply take advantage of the fact that the binary representation of all the numbers from 0 through 255 cover every permutation.

for (int i=0; i<256; i++) {
    System.out.println(Integer.toBinaryString(i));
}

Solution 2

Just print the for variables (i...p) without accessing this obscure empty array.

Solution 3

Well, if it's OK to use some built-in classes, you can do this in the following way:

for (int i=0; i<256; i++){
    System.out.println(Integer.toBinaryString(i));
}

And the second way (I believe you should use it, because looking by looking at it you can understand what's under the hood instead of "some magic", it uses bit mask):

for (int i=0;i<256;i++){
    int mask = 256;
    while (mask > 0){
        if ((mask & i) == 0){
            System.out.print("0");
        } else {
            System.out.print("1");
        }
        mask = mask >> 1;
    }
    System.out.println();
}

Comments

[user2411290]

My instructions were: "You can use nested loops, if your familiar with how base 2 works, you can program it by extracting the base 2 digits; if you're familiar with bit manipulation operators, you could use them to output the values." I'm just trying to do it in a way that makes the most sense for me conceptually.

[Marko Topolnik]

From the deleted answer by Asaph: System.out.println("" + i + j + k + l + m + n + o + p);

[user2411290]

Thank you very much. This is somewhat embarrassing that I don't know how to do this, but I will make sure to study/practice it until I do. Thanks for your help.

[user2411290]

Thanks for your help, nikis!

[user2411290]

Thanks for helping me out!

[Marko Topolnik]

BTW your one-liner won't be satisfactory because leading zeros are important to meet the requirement.

[nikis]

@user2411290 I've added the second way - it should be used in education purposes instead of "some magic", it uses bit manipulation

[Asaph]

@MarkoTopolnik To get the zero padding: stackoverflow.com/a/4421438/166339 . Accepted answer is kinda ugly but satisfies the requirement.