Print all combinations
Why a string array . Just a String would suffice.
Do we really need to store it in arrays. The computed arrays would only be usde to display. So we can work towards a display method instead of storing and displaying them.

int i;
for(i=1;i&lt;26;i++){
    System.out.print(i+", ");
    System.out.print(Character.toString((char)(64+i))+", ");
}
System.out.print(i+", ");
System.out.println(Character.toString((char)(64+i))+".");

StringBuilder next = new StringBuilder();
for(i=1;i&lt;26;i++){
    System.out.print(i+", ");
    next.append(Character.toString((char)(64+i)) + ", ");
    System.out.print(next);
}
System.out.print(i+", ");
next.append(Character.toString((char)(64+i)));
System.out.println(next);
// Time complexity: O(n)
// Space complexity: O(n+m*(m+1)/2))

Assuming we are striving to have a generic implementation wherein we have two input arrays and we wish to provide the output. Even in that case we can carry forward with above implementation with slight changes.
Having the last condition check seems an unneeded overhead. Instead we loop in for last-but-one index and print the last outside.

if ((i + 1) == result.length)