Counting from 0 to a number and back to zero, and space-padding the result to be a given length
You can simplify the logic that prints the numbers going from 0 to number anc back to 0.

They are: number - Math.abs(number - x). Let's explain why. With the number 5, the wanted output is:

01234543210


As a pre-requisite, let's consider the (simpler) output

54321012345


We want to model that with a single variable x going from 0 to 2 * number. Clearly, there are 2 paths: one decreasing and one increasing.

                     5   4   3   2   1   0   1   2   3   4   5
value of x           0   1   2   3   4   5   6   7   8   9   10
value of 5 - x       5   4   3   2   1   0  -1  -2  -3  -4  -5
value of abs(5 - x)  5   4   3   2   1   0   1   2   3   4   5  &lt;-- output


Now that we have that, it is clear that our real wanted output is simply 5 minus that one, i.e. number - Math.abs(number - x).

Putting this into code:

public static void counter(int number, int length) {
    int space = (length - number * 2 + 1) / 2;
    for (int a = 0; a &lt; space; a++) {
        System.out.print(" ");
    }
    for (int x = 0; x &lt;= number * 2; x++) {
        System.out.print(number - Math.abs(number - x));
    }
    for (int b = 0; b &lt; space; b++) {
        System.out.print(" ");
    }
}


Other comments:


Add spaces before each operator, it adds to readability.
Don't use a mixed form of curly braces and single line statement. Either add curly braces everywhere and then have a proper line break or make it a single line without them.
There is no need to store into local variables when you only use it once. In this case having numberFull and spaceFull don't really add to clarity and it is much simpler to have int space = (length - number * 2 + 1) / 2;.
There is no validation on the number and the count of spaces. You might want to add some.
Instead of letting the counter method print the String directly, it would be better to let it build the String and return it. The caller can then decide to print it or not. For that, take a look at the StringBuilder class.