Apart from all these answers the problem with your code was that you are not clearing the string before reversing it. So before the for loop just put s = ""
and you code should work fine.. :)
Based on comment
public class ConvertBinary {
public static String convertBinary(int n) {
String s = "";
while (n > 0) {
s += (n % 2);
n = n / 2;
}
int len = s.length();
String[] binary = s.split("");
String[] binaryCopy = new String[s.length()];
s = "";
for (int i = 0; i < len; i++) {
binaryCopy[i] = binary[len - i - 1];
s += binaryCopy[i];
}
return s;
}
public static void main(String args[]) {
int num = 4;
System.out.println(convertBinary(num));
System.out.println(Integer.toBinaryString(num));
}
}