Help here!!

what's wrong in this code:

import java.io.*;

public class WriteFile{

public static void main(String[] args) throws IOException{
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));

FileOutputStream fop = new FileOutputStream(f);
File f = new File("textfile1.txt");
System.out.print("Enter your name: ");
String winner1 = input.readLine();

System.out.print("Enter name1");
String winner2 = input.readLine();
System.out.print("Enter name2");
String winner3 = input.readLine();
System.out.print("Enter name3");
String winner4 = input.readLine();
System.out.print("Enter name4");

if(f.exists()){
String str= winner1;
String str2= winner2;
String str3= winner3;
String str4= winner4;

fop.write(str.getBytes());
fop.write(str2.getBytes());
fop.write(str3.getBytes());
fop.write(str4.getBytes());

fop.flush();
fop.close();
System.out.println("The data has been written");
}

else
System.out.println("This file is not exist");
}
}