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How to implement hasNext() method with BufferedReader + StringTokenizer?

I have this fast reader class:
static class FastReader {
BufferedReader br;
StringTokenizer st;
public FastReader() {
br = new BufferedReader(new InputStreamReader(System.in));
}
String next() {
while (st == null || !st.hasMoreElements()) {
try {
st = new StringTokenizer(br.readLine());
}
catch (IOException e) {
e.printStackTrace();
}
}
return st.nextToken();
}
int nextInt() {
return Integer.parseInt(next());
}
long nextLong() {
return Long.parseLong(next());
}
double nextDouble() {
return Double.parseDouble(next());
}
String nextLine() {
String str = "";
try {
str = br.readLine();
}
catch (IOException e) {
e.printStackTrace();
}
return str;
}
int[] readArray(int n) {
int[] a = new int[n];
for(int i=0; i<n; i++) {
a[i] = nextInt();
}
return a;
}
}
I want to stop reading input as soon as I reach end of file. I know this can be done using scanner hasNext() method, How can I implement the same method for my reader class?
PS. I want to read input for this question:
https://www.spoj.com/problems/COINS/

You can set a mark() then try to read a line, if it is successful you could reset() to where you set the mark and return true and false otherwise.
You would also have to check if the current tokenizer has more tokens left. For example:
boolean hasNext() {
if (st != null && st.hasMoreTokens()) {
return true;
}
String tmp;
try {
br.mark(1000);
tmp = br.readLine();
if (tmp == null) {
return false;
}
br.reset();
} catch (IOException e) {
return false;
}
return true;
}
mark() takes readAheadLimit argument to limit the number of characters that can be read while having that mark set, you could increase that if you're dealing with long lines.

You can cover your code in a while loop with the condition that the user input is not null.
Example:
BuffedReader br = new BufferedReader(new InputStreamReader(System.in);
String key = "";
while((key = br.readLine()) != null)
{
//your code
}

Why I could not save the contents of a file after reading it twice?

Already fixed. Thanks for Mas & ruhul for observing my bugs.
I was trying to read a text file twice, named stationary.txt. The contents of the file has three columns such as the amount, the name of product and the total price.
What I am trying to do first is by averaging each product's price by reading line by line. Then I closed the Buffered and then open it again and read. The second reading takes a variable average and compares each product's price line by line. If line 1 is over the average, then write it into dearer.txt, otherwise write it into cheap.txt
Here is the stationary.txt
1 Highlighter 5.99
2 Pen 9.00
3 Eraser 5.00
4 DrawingPin 2.75
5 Highlighter 10.99
6 FountainPen 20.50
7 Pencil 14.50
Below is the source code
import java.util.*;
import java.io.*;
public class Ques {
public static void main(String[] args) throws FileNotFoundException {
double average = 0;
File inFile = new File("stationary.txt");
FileReader fileReader = new FileReader(inFile);
BufferedReader bufReader = new BufferedReader(fileReader);
File outFilel = new File("dearer.txt");
FileOutputStream outFileStreaml = new FileOutputStream(outFilel);
PrintWriter outStream1 = new PrintWriter(outFileStreaml);
File outFile2 = new File("cheap.txt");
FileOutputStream outFileStream2 = new FileOutputStream(outFile2);
PrintWriter outStream2 = new PrintWriter(outFileStream2);
computeAverage(bufReader, outStream1, outStream2, average);
}
public static void computeAverage(BufferedReader bufReader, PrintWriter outStream1, PrintWriter outStream2, double average) {
String line = "";
double mark = 0;
double sum = 0;
int count = 0;
try {
bufReader.readLine();
while ((line = bufReader.readLine()) != null) {
String [] data = line.split(" ");
mark = Double.parseDouble(data[2]);
sum += mark;
count++;
}
average = sum / count;
compareMark(outStream1, outStream2, average);
} catch (NumberFormatException | IOException e) {
System.out.println(e);
} finally {
if (bufReader != null) {
try {
bufReader.close();
} catch ( IOException e) {
e.printStackTrace();
}
}
}
}
public static void compareMark(PrintWriter outStream1, PrintWriter outStream2, double average) throws FileNotFoundException {
File inFile = new File("stationary.txt");
FileReader fileReader = new FileReader(inFile);
BufferedReader bufReader = new BufferedReader(fileReader);
String line = " ";
double sum = 0;
double mark = 0;
int count = 0;
try {
double ave = (double) Math.round(average * 100) / 100;
System.out.println("another " + ave);
bufReader.readLine();
while ((line = bufReader.readLine()) != null) {
System.out.println(line);
String [] data = line.split(" ");
mark = Double.parseDouble(data[2]);
if (mark > ave) {
System.out.println("Over");
outStream1.write(line);
} else {
System.out.println("Less");
outStream2.write(line);
}
}
} catch (IOException e) {
System.out.println(e);
} catch (NumberFormatException ex) {
System.out.println(ex);
} finally {
if (bufReader != null) {
try {
bufReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
The source code is perfectly working, just that I received 0 bytes of both files after executing reading twice (first, doing average and last, doing comparison). Why is that? what am I doing wrong here?
Thank you for your kind help.

Your code is not correct and does not compile. But the main flaws are the following:
Your Double.parseDouble(data[2]) shouldn't work with your 4th line of data. Better use Double.parseDouble(data[data.length - 1])
Remove the readLine()-calls in front of the while-loop.
Write the lines including a line separator.
Close the OutStreams

The Data File that you have provided have the columns seperated by a space. As the 2nd Column has data which contains spaces, the convertion of data[2] to double will trigger an exception. Which will make the program to close the buffers and exit.
Use Commas to seperate column data.
Use better exception handling to find exceptions easily.

All you need is to close those output stream. As you are using bufferredWriter and not flushing it after each write you need to close those output-stream. which will write back those lines or datas into the file. Here is an example how you can do it:
Example 1: using flush().
....
outStream1.write(line);
outStream1.flush();
} else {
System.out.println("Less");
outStream2.write(line);
outStream2.flush();
}
Example 2: most efficient (either way you need to close those buffer too like bufReader.close())
...
} catch (IOException e) {
System.out.println(e);
} catch (NumberFormatException ex) {
System.out.println(ex);
} finally {
// add try catch.
outStream2.close();
outStream1.close();
if (bufReader != null ... ) {
try {
bufReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

As requested, an example using List
First a class to hold the stationary data, must be completed:
public class Stationary {
private final int id; // or String if desired
private final String name;
private final double mark; // BigDecimal would be better for money
public Stationary(int id, String name, double mark) {
// TODO error checking
this.id = id;
...
}
public int getId() {
return id;
}
... // TODO other getters
// TODO equals, hashCode, toString
}
and to read the file:
public List<Stationary> read(File file) {
List<Stationary> list= new ArrayList<>();
try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
String line;
while ((line = reader.readLine()) != null) {
// TODO parse line into id, name, mark
list.add(new Stationary(id, name, mark);
}
}
return list;
}
now the list can be used as needed, e.g. average:
List<Stationary> stationaries = read(STATIONARY_FILE);
...
for (Stationary stationary : stationaries) {
sum += stationary.getMark();
count += 1;
}
...
streams not used to keep it simple

finding the number of occurrences for a specific char using recursion

This code below is part of a program, that will find the number of occurrences of the input character in a text file
public static void main(String[] args){
[...]
java.io.File file1=new java.io.File(dirPath1);
FileInputStream fis = new FileInputStream(file1);
System.out.println(" return "+rec(sc.next().charAt(0),fis));
}
public static int rec (char ch, FileInputStream fis)throws IOException{
char current=0;
if(fis.available()==0){
return 0;
}
if(fis.read()!=-1){
current = (char) fis.read();
}
if(current==ch) {
return 1+rec(ch,fis);
}else
return rec(ch,fis);
}
}
The problem is:
If the file has one character, and ch=that one character. it returns 0, when I traced the code I found that it doesn't enter if(current==ch). Although, they are the same char.
if there is more than on character,strings some of them-the matches chars- will enter if block and others won't.
How can I fix this ?
Is there another way to find the number of occurrences recursively ?
another question: should I use try and catch in rec method to catch IOException ?
Thanks in advance
P.S. this program is from assignment,I have to use recursion and compare it with iteration.

you call fis.read() twice first one read first character and second one read nothing
this is your answer
public static int rec(char ch, FileInputStream fis) throws IOException {
char current = 0;
if (fis.available() == 0) {
return 0;
}
int read = fis.read();
if (read != -1) {
current = (char) read;
}
if (current == ch) {
return 1 + rec(ch, fis);
}
else
return rec(ch, fis);
}

My suggestion would be as follows:
Read the whole text file into a java.lang.String
Then use the library Apache Commons Lang and use this method for counting the occurrences:
http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html#countMatches-java.lang.CharSequence-java.lang.CharSequence-

You should use FileReader to read chars from text file.
Reader reader = new FileReader("MyFile.txt");
I think using while ((i=reader.read()) != -1) is a better approach instead of three if and an else.
So you can achieve this with fewer lines of code:
public static int rec (char ch, Reader reader)throws IOException{
char current=0;
int i;
while ((i=reader.read()) != -1) {
current = (char) i;
if(current==ch) {
return 1+rec(ch,reader);
}else
return rec(ch,reader);
}
return 0;
}
I think there is no need to use try and catch in rec method to catch IOException. I have used it here:
try {
Reader reader = new FileReader("MyFile.txt");
System.out.println(" return " + rec('a', reader));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Do-while loop not paying attention to the while in java

I'm trying to write a do while loop that will read a file that the user input and read it out and will loop until the user types end. The do part is working, but my while just isn't being activated and I'm struggling to figure out why.
public static void readingFiles() throws Exception {
BufferedReader reader = null;
Scanner input = null;
boolean fileFound = true;
do {
System.out.print("Enter a file name or Type END to exit: ");
input = new Scanner(System.in);
if(input.hasNextLine())
{
try {
File f = new File(input.nextLine());
reader = new BufferedReader(new FileReader(f));
String str = null;
while((str = reader.readLine()) != null)
{
System.out.println(str);
}
}
catch (FileNotFoundException e)
{
System.out.println("File Not Found. Please try again.");
fileFound = false;
continue;
}
catch (IOException e)
{
System.out.println("There was an IOException. Please try again.");
continue;
}
catch (Exception e)
{
System.out.println("There was an exception. Please try again.");
continue;
}
finally
{
{
if(fileFound)
reader.close();
}
}
}
} while(!input.nextLine().equalsIgnoreCase("end"));
}
I've tried using an if statement before my input.hasNextLine() but then it would ignore the rest of the whole program and do nothing and only typing end would work. I've tried using && in my current if statement too but that didn't work. And I tried using a boolean that I set to true if string contained end. I think the problem may be in the input.hasNextLine but I'm not sure why or what to change it to?
Thanks for any help

Calling input.nextLine() again will not preserve your previous input string.
Store it in a variable, and compare that
public static void readingFiles() throws Exception {
BufferedReader reader = null;
String filename = null;
Scanner input = new Scanner(System.in);
boolean fileFound = true;
do {
System.out.print("Enter a file name or Type END to exit: ");
if(input.hasNextLine()) {
filename = input.nextLine();
try {
File f = new File(filename);
// reader =
...
} while (!filename.equalsIgnoreCase("end");

Need my program to know where I left off

So I'm trying to make clip card application. In other words, I'm making an application that counts how many coffees a customer purchases, and for every 10:th purchase the customer gets awarded a free one. I'm pretty much done with the loop, but I'm having difficulties with figuring out how to make my program remember where I left off. For example, lets say I have bought my 7th coffee and am leaving so I want to close the application; is there a way for the program to remember where to continue next time it is being run?
Here's what I have so far:
import java.util.Scanner;
public class FelixNeww {
public static void main(String [] args) {
Scanner key;
String entry;
int count = 0;
String password = "knusan01";
while(true) {
System.out.println("Enter password: ");
key = new Scanner(System.in);
entry = key.nextLine();
if(entry.compareTo(password) == 0){
count++;
System.out.println("You're one step closer to a free coffe! You have so far bought "
+ count + " coffe(s)");
}
if(count == 10 && count != 0){
System.out.println("YOU'VE GOT A FREE COFFE!");
count = 0;
}
if(entry.compareTo(password) != 0){
System.out.println("Wrong password! Try again.\n");
}
}
}
}
Thanks

If you want to make sure the progress is saved, try looking into the RuntimeHook as said here: Intercepting java machine shutdown call?
And what you need to do is store the data in a file, the current count. This can be done fairly easily with the following code:
public void saveToFile(int count)
{
BufferedWriter bw = null;
try
{
bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("countStorage"))));
bw.write(count);
}
catch(IOException e)
{
e.printStackTrace();
}
finally
{
if(bw != null)
{
try
{
bw.close();
}
catch(IOException e) {}
}
}
}
public int readFromFile()
{
BufferedReader br = null;
try
{
br = new BufferedReader(new InputStreamReader(new FileInputStream(new File("countStorage"))));
String line = br.readLine();
int count = Integer.parseInt(line);
return count;
}
catch(IOException e)
{
e.printStackTrace();
}
finally
{
if(br != null)
{
try
{
br.close();
}
catch(IOException e) {}
}
}
}