Develop Reference

How to sum up all ints in a text file?

I need to pull integers from a text file and sum them up. I came up with this but I keep getting an error. What am I missing? I need to use a scanner class.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class txtClass {
public static void main(String[] args) throws FileNotFoundException {
File txtFile = new File(//text file path//);
Scanner scan = new Scanner(txtFile);
int length = 0;
while(scan.hasNextLine()) {
scan.nextLine();
length++;
}
int array[] = new int [length];
array[length++] = scan.nextInt();
System.out.println(array.toString());
int h = 0;
for (int i = 0; i<array.length; i++)
{
h +=array[i];
}
scan.close();
System.out.print(h);
}
}

As suggested, a lot of the code is not really needed. But presumably the 'error' you get is array index out of bounds. Here:
int array[] = new int [length];
array[length++] = scan.nextInt();
So you allocate an array and immediately access off the end of the array. Let's assume length is 42. Therefore, the allocated array elements have indexes 0 to 41. You try and assign something to array[42]. I'm not sure what you're trying to do with that line.
The alternative guess (which we would not need to guess had you mentioned the actual error message) is that your counting lines leaves the scanner positioned at end of file. so the scan.nextInt() call in the assignment gets you an I/O error.
In any case, the core of the solution is something like
int sum = 0;
while (scan.hasNextInt())
sum += scan.nextInt();
No array is needed.

You wrote in your question
I keep getting an error
That would be NoSuchElementException which is thrown by this line of your code:
array[length++] = scan.nextInt();
This is because you have already scanned the entire file and therefore there is no next int.
Remember that in order for people to help you with errors thrown by your code, you need to post the actual exception and the stack trace as well as your code.
You don't need to save all the numbers in the file in an array in order to get the sum of all the numbers. However if you also want to save all the numbers but you don't know in advance how many there are, you can use a List.
Here is a minimal example of how to read the file – which I assume contains only numbers separated by whitespace – and calculate the total. Of-course you need to replace text file path with the actual path to the text file.
File txtFile = new File("text file path");
try (Scanner scan = new Scanner(txtFile)) {
int total = 0;
while (scan.hasNextInt()) {
total += scan.nextInt();
}
System.out.println("Total: " + total);
}
catch (FileNotFoundException xFileNotFound) {
xFileNotFound.printStackTrace();
}
Note that the above code uses try-with-resources.

How to read both integers and doubles from txt fle

i have a text file and i want to read the integers and doubles. I dont know how many values i have to read. The first value in the line is always the integer and the second is always the double. I want to save the value of the first line seperately.
200
11010 0.004
500 0.02
637 0.018
How to create 2 arrays and save the values, so i can use them later? I am not allowed to create a new class. I tried to use Point but cant store doubles.
Scanner scanner = new Scanner(new File(args[0]));
int cores= scanner.nextInt();
System.out.print(cores);
while (scanner.hasNext()) {
int x = scanner.nextInt();
double y = scanner.nextDouble();
System.out.printf("x");}
I' ve tried the code above but throws out Exception

You can use simple file handling approach to read the file line by line, For the first line you can use a flag to mark the line and sent the file to remote location you want to save the data. Then for all later lines you can split the string on the basis of " " (space). Post which once you have stripped the elements of the resulting array you can typecast and append the element at first index to integer array. And the second element (typecast before append) to the double array. This shall work absolutely fine with any length of file.
A demo code for the same is as following:
public class ReadLineByLine
{
public static void main(String args[])
{
try
{
FileInputStream fis=new FileInputStream("Demo.txt");
Scanner sc=new Scanner(fis);
String tempLineData = "";
int flag = 0;
String[] elements;
List<Integer> ints = new ArrayList<Integer>(
List<Float> floats = new ArrayList<Float>(
while(sc.hasNextLine())
{
if(flag == 0){
// Place the operation with the first line here
flag++;
}
tempLineData=sc.nextLine();
elements = tempLineData.split(" ");
ints.add((int)elements[0].trim());
floats.add((float)elements[1].trim());
}
sc.close();
}
catch(IOException e)
{
e.printStackTrace();
}
}
}

How to avoid a "java.util.NoSuchElementException" crashing my program

TL;DR-- how to get a java.util.NoSuchElementException to return a null instead of error and crash the program.
I was writing a program that is supposed to read a series of ints from a text file. In the program the amount of ints will vary each time I run it. I have written a piece of code that will read ints and I want to know how to make the java.util.NoSuchElementException not crash my program and instead return a null.
The code I have writen is as follows
public static void main(String[] args) throws IOException{
Scanner Input = new Scanner(new File("newestcode.txt"));
Integer[] digits = new Integer[100];
int h = 0;
while(true){
digits[h] = Input.nextInt();
h++;
System.out.println(digits[h]);
}
}
in case you are curious, the program I am to be writing is a sort of decryption engine for a bad encryption engine I wrote the other day

try {
digits[h] = Input.nextInt();
h++;
System.out.println(digits[h]);
}catch (NoSuchElementException e){
break;
}

First of all, if you're not sure about amount of ints in your file, don't try to store them into fixed-size array. Use ArrayList instead.
Also don't use endless loop while(true) but consider using Input.hasNext() to check if there still is something to read from file.
And one more. You're trying to print value after increment. This means that you're adding element on 0 position but trying to read it from 1 position. Make increment on the end of the loop.
Scanner Input = new Scanner(new File("newestcode.txt"));
List<Integer> digits = new ArrayList<>();
int h = 0;
while(Input.hasNetxt()){
digits.add(h, Input.nextInt());
System.out.println(digits.get(h));
h++;
}

You should use the input.hasNext() method to check whether the input has any more 'int' before using it.
In order to support any length of int elements, you cannot set the array to a fixed length of 100, you need to use an ArrayList to add elements dynamically.
Scanner input = new Scanner(new File("./newestcode.txt"));
List<Integer> digits = new ArrayList<>();
int h = 0;
while (input.hasNext()) {
digits.add(h, input.nextInt());
System.out.println(digits.get(h));
h++;
}
Note: You need to print digits[h] before increasing the h.

Printing lines in reverse java

I'm trying to wrap my head around a problem I have in a programming set.
We're supposed to write code that reads from a file and prints it out. I get that, I can do it.
What he wants us to do is have it print out in reverse.
the file reads:
abc
123
987
He wants:
987
123
abc
The code, as it is, is as follows:
{
FileReader n=new FileReader("F:\\Java\\Set 8\\output1.txt");
Scanner in=new Scanner(n);
int l;
while (in.hasNext())
{
l=in.nextInt();
System.out.println(l);
}
in.close();
}
}
Yes, I am using java.io.*; and Scanner.
What would be the simplest way to do this?
EDIT EDIT EDIT
Here's the improved code, where I try to put it into an array.
The data in the array isn't printing out.
public static void main(String[] args) throws IOException
{
int[]Num=new int[20];
Scanner in=new Scanner(new FileReader("F:\\Java\\Set 8\\output1.txt"));
int k;
for (k=0;k<20;k++)
{
Num[k]=in.nextInt();
}
//in.close();
for (k=20;k<20;k--)
{
System.out.print(+Num[k]);
}
//in.close();
}

The most simplest way is to construct a List and add each line to the list while reading from the file. Once done, print the list items in reverse.
Here is my version of code for your problem.
public static void main(String[] args) throws FileNotFoundException {
FileReader n = new FileReader("/Users/sharish/Data/abc.xml");
Scanner in = new Scanner(n);
ArrayList<String> lines = new ArrayList<String>();
while (in.hasNext()) {
lines.add(in.nextLine());
}
in.close();
for (int i = lines.size() - 1; i >= 0; i--) {
System.out.println(lines.get(i));
}
}

Use Stack.
public static void displayReverse() throws FileNotFoundException {
FileReader n=new FileReader("C:\\Users\\User\\Documents\\file.txt");
Scanner in=new Scanner(n);
Stack<String> st = new Stack<String>();
while (in.hasNext()) {
st.push(in.nextLine());
}
in.close();
while(!st.isEmpty()) {
System.out.println(st.pop());
}
}

If you are permitted the use of third party APIs, Apache Commons IO contains a class, ReversedLinesFileReader, that reads files similar to a BufferedReader (except last line first). Here is the API documentation: http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/input/ReversedLinesFileReader.html
Another (less efficient) solution is hinted at in the comments. You can read your entire file into an ArrayList, reverse that list (e.g. by pushing its contents onto a stack and then popping it off), and then iterate through your reversed list to print.
EDIT:
Here is a crude example:
ArrayList<String> lines = new ArrayList<String>();
Scanner in = new Scanner(new FileReader("input.txt"));
while (in.hasNextLine())
{
lines.add(in.nextLine());
}
Use an ArrayList instead of a static array. We don't necessarily know the length of the file in advance so a static array doesn't make sense here. http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
Your example input 123, abc, etc, contains characters as well as ints, so your calls to hasNextInt and nextInt will eventually throw an Exception. To read lines use hasNextLine and nextLine instead. These methods return String and so our ArrayList also needs to store String. http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextLine()
Once the file is in a list (not a good solution if the file is large - we've read the entire file into memory) we can either reverse the list (if keeping a reversed form around makes sense), or just iterate through it backwards.
for (int i=lines.size()-1; i>=0; i--) // from n-1 downTo 0
{
String line = lines.get(i);
System.out.println( line );
}

public static void main(String[] args) throws Exception{
String fileName = "F:\\Java\\Set 8\\output1.txt";
RandomAccessFile raf = new RandomAccessFile(fileName,"r");
int len = (int) raf.length();
raf.seek(len);
while(len >= 0){
if(len == 0){
raf.seek(0);
System.out.println(raf.readLine());
break;
}
raf.seek(len--);
char ch = (char)raf.read();
if(ch == '\n'){
String str = raf.readLine();
System.out.println(str);
}
}
}

try using org.apache.commons.io.input.ReversedLinesFileReader, it should do what you want.

You could read the lines like you are already doing, but instead of printing them (because that would print them in order and you need it the other way around), add them to some memory structure like a List or a Stack, and then, in a second loop, iterate this structure to print the lines in the needed order.

Using your code and the answers in the comments, here's an example of how you would store the strings into the arraylist and then print them out in reverse (building off of your own code)
{
FileReader n=new FileReader("F:\\Java\\Set 8\\output1.txt");
Scanner in=new Scanner(n);
int l;
ArrayList<String> reversed = new ArrayList<String>(); // creating a new String arraylist
while (in.hasNext())
{
l=in.nextInt();
System.out.println(l);
reversed.add(l); // storing the strings into the reversed arraylist
}
in.close();
// for loop to print out the arraylist in reversed order
for (int i = reversed.size() - 1; i >= 0; i--) {
System.out.println(reversed.get(i));
}
}
}

Using Java 8:
try(PrintWriter out =
new PrintWriter(Files.newBufferedWriter(Paths.get("out.txt")))) {
Files.lines(Paths.get("in.txt"))
.collect(Collectors.toCollection(LinkedList::new))
.descendingIterator()
.forEachRemaining(out::println);
}

Printing values from array after I split the values?

I'm want to read in from a file and then split it into separate parts and then access it and print it out. I know i can't do it the way it looks now. Please reply asap. The object of the program is to read in from a file points where i split it into x and y values, then sort these values according to there polar_order(this i have figured out) i just want to print out the values for testing.
Thanks
public static void main(String[] args){
int count = 0;
Scanner read = new Scanner(System.in);
int N = read.nextInt();
while(read.hasNext()){
String nN = read.nextLine();
String[]cord = nN.split(" ");
int x = Integer.parseInt(args[0]);
int y = Integer.parseInt(args[1]);
count++;
}
read.close();
for(int i = 0; i<N;i++){
System.out.print(x[i]);
}

Hope you are trying to print the contents of the string array 'cord'.
Try this code:
string dataToPrint = string.Join(" ", cord);

Not sure how you've structured your file but if you want to read in a file, here's an indication of how you might do that. Replace the while method with the method you need to extract the x, y values... you should probably apply Nist's answer to do so (use an ArrayList).
try {
Scanner s = new Scanner(new File("your file path"));
while (s.hasNextLine()) {
System.out.println(s.nextLine());
}
s.close();
}
catch (Exception e) {
System.out.println(e.getMessage());
}

I've found the easiest way to print the contents of an array (assuming it's not null) is this:
System.out.println(Arrays.toString(array));
For some odd reason, most of the list classes give nice output:
[1, 2, 3]
whereas arrays gives you a type/address indicator:
[Ljava.lang.String;#10b62c9
I've never quite understood why they didn't do something so that arrays had nicer output without having to call some utility function.