REALLY need help with new lines

Question

Ok,
I have been thinking for hours and cannot find the solution to my problem.
My issue is that when I write text to a file:
...Initiate bufferedwriter
bw.write("CODE");
bw.write(System.getProperty("line.separator"));
bw.write("CODE2");...it comes out normal, but when I read it:
..Initiate bufferedreader
String st=br.readLine();
String st2=br.readLine();st comes out as CODECODE2
st2 comes out as null
WHAT AM I DOING WRONG???????????????????

Answer 1

EXACT snippets from the program:
String[] fin=st.split("\n");
for(int i=0;i<fin.length;i++) {
                fos.write(fin);
fos.write(System.getProperty("line.separator"));
fos.flush();
fos.close();
fw.close();
(st is text to write)String st=br.readLine();
while(true) {
String st2=br.readLine();
if(st2==null) {
break;
else{st=st+st2+System.getProperty("line.separator");}
br.close();