There are a couple ways you can reverse a string to make it backwards.

1. StringBuilder/StringBuffer:

String code = "code";
System.out.println(code);

StringBuilder sb = new StringBuilder(code); 
code = sb.reverse().toString();

System.out.println(code);

1. Char array:

String code = "code";
System.out.println(code);

char[] array = code.toCharArray();
for (int index = 0, mirroredIndex = array.length - 1; index < mirroredIndex; index++, mirroredIndex--) {
    char temp = array[index];
    array[index] = array[mirroredIndex];
    array[mirroredIndex] = temp;
}

// print reversed
System.out.println(new String(array));