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What is wrong in my file reading with Scanner class?

Every time I run it, gives this message (( InputMismatchException )) where is the problem from ?
File f = new File("nameList.txt");
try {
PrintWriter out;
out = new PrintWriter(f);
for (int i = 0; i < 4; i++) {
out.printf("Name : %s Age : %d ", "Rezaee-Hadi", 19);
out.println("");
}
out.close();
} catch (IOException ex) {
System.out.println("Exception thrown : " + ex);
}
try {
Scanner in = new Scanner(f);
String name = in.nextLine();
int age = in.nextInt();
for (int i = 0; i < 4; i++) {
System.out.println(name);
System.out.println(age);
}
in.close();
} catch (FileNotFoundException ex) {
System.out.println("Exception thrown : " + ex);
}

You are creating your data file in the following data format:
Name : Rezaee-Hadi Age : 19
Now, it really doesn't matter (to some extent) how you format your data file as long as you realize that you may need to parse that data later on. You really don't need to maintain a header with your data on each file line. We already know that the first piece of data on any file line is to be a Name and the second piece of data on any file line is to be the Age of the person the Name relates to. So, the following is sufficient:
Rezaee-Hadi, 19
If you want, you can place a header as the very first line of the data file so that it can easily be determined what each piece of data on each line relates to, for example:
Name, Age
Rezaee-Hadi, 19
Fred Flintstone, 32
Tom Jones, 66
John Smith, 54
This is actually a typical format for CSV data files.
Keeping with the file data format you are already using:
There is nothing wrong with using the Scanner#nextLine() method. It's a good way to go but you should be iterating through the file line by line using a while loop because you may not always know exactly how many actual data lines are contained within the file, for example:
Scanner in = new Scanner(f);
String dataLine;
while (in.hasNextLine()) {
dataLine = in.nextLine().trim();
// Skip Blank Lines
if (dataLine.equals("")) {
continue;
}
System.out.println(dataLine);
}
This will print all the data lines contained within your file. But this is not what you really want is it. You want to separate the name and age from each line which means then that you need to parse the data from each line. One way (in your case) would be something like this:
String dataLine;
Scanner in = new Scanner(f);
while (in.hasNextLine()) {
dataLine = in.nextLine().trim();
// Skip Blank Lines
if (dataLine.equals("")) {
continue;
}
String[] dataParts = dataLine.replace("Name : " , "").split(" Age : ");
System.out.println("The Person's Name: " + dataParts[0] + System.lineSeparator()
+ "The Person's Age: " + dataParts[1] + System.lineSeparator());
}
In the above code we iterate through the entire data file one line at a time using a while loop. As each line is read into the dataLine string variable it is also trimmed of any leading or trailing whitespaces. Normally we don't want these. We then check to make sure the line is not blank. We don't normally want these either and here we skip past those blank lines by issuing a continue to the while loop so as to immediately initiate another iteration. If the file line line actually contains data then it is held within the dataLine variable.
Now we want to parse that data so as to retrieve the Name and the Age and place them into a String Array. We do this by using the String#split() method but first we get rid of the "Name : " portion of the line using the String#replace() method since we don't want to deal with this text while we parse the line. In the String#split() method we supply a string delimiter to split by and that delimiter is " Age : ".
String[] dataParts = dataLine.replace("Name : " , "").split(" Age : ");
Now when each line is parsed, the Name and Age will be contained within the dataParts[] string array as elements located at index 0 and index 1. We now use these array elements to display the results to console window.
At this point the Age is a string located in the dataParts[] array at index 1 but you may want to convert this age to a Integer (int) type value. To do this you can utilize the Integer.parseInt() or Integer.valueOf() methods but before you do that you should validate the fact the the string you are about to pass to either of these methods is indeed a string numerical integer value. To do this you would utilize the String#matches() method along with a simple little Regular Expression (RegEx):
int age = 0;
if (dataParts[1].matches("\\d+")) {
age = Integer.parseInt(dataParts[1]);
// OR age = Integer.valueOf(dataParts[1]);
System.out.println("Age = " + age);
}
else {
System.out.println("Age is not a numerical value!");
}
The regular expression "\\d+" placed within the String#matches() method basically means, "Is the supplied string a string representation of a integer numerical value?". If the method finds that it is not then boolean false is returned. If it finds that the value supplied is a string integer numerical value then boolean true is returned. Doing things this way will prevent any NumberFormatException's from occurring.

Replace this:
int age=0;
while (in.hasNext()) {
// if the next is a Int,
// print found and the Int
if (in.hasNextInt()) {
age = in.nextInt();
System.out.println("Found Int value :"
+ age);
}
}
in place of this:
int age = in.nextInt();
Then you will not get "InputMismatchException" anymore..

How to add each value to a separate line?

My code does read and write the file, but it is not on a new line for every value and instead prints every value in one line.
// 2 points
static void Q1(String inputFilename, String outputFilename) {
// You are given a csv file (inputFilename) with all the data on a single line. Separate the
// values by commas and write each value on a separate line in a new file (outputFilename)
String data = "";
try {
for(String s :Files.readAllLines(Paths.get(inputFilename))){
data = data + s;
}
Files.write(Paths.get(outputFilename), data.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
As such the grader says:
Incorrect on input: [data/oneLine0.csv, output0.txt]
Expected output : overwrought plastic bomb
wrapped litter basket
obstetric matter of law
diabetic stretching
spatial marathi
continental prescott
reproductive john henry o'hara
hollow beta blocker
stereotyped national aeronautics and space administration
irremediable st. olaf
brunet fibrosis
embarrassed dwarf elm
superficial harrier
disparaging whetstone
consecrate agony
impacted lampoon
nefarious textile
some other organisation
Your output : overwrought plastic bomb,wrapped litter basket,obstetric matter of law,diabetic stretching,spatial marathi,continental prescott,reproductive john henry o'hara,hollow beta blocker,stereotyped national aeronautics and space administration,irremediable st. olaf,brunet fibrosis,embarrassed dwarf elm,superficial harrier,disparaging whetstone,consecrate agony,impacted lampoon,nefarious textile,some other organisation

String data = "";
try {
// input file has all data on one line, for loop isn't necessary here
// input file has elements separated by comma characters
for(String s : Files.readAllLines(Paths.get(inputFilename))){
data = data + s;
}
String[] separated = data.split(",");// does not handle embedded commas well
data = "";
// output file should have each comma separated value on its own line
for (String t : separated) {
data = data + t + System.getProperty("line.separator");
}
Files.write(Paths.get(outputFilename), data.getBytes());
}

First of all, you need to remove the comma from the CSV file. I'd suggest using
s = s.replace(",",""); Additionally, you must append a \n to each string to make it appear on a new line. So, you should add s += "\n"; This yields the code:
// 2 points
static void Q1(String inputFilename, String outputFilename) {
// You are given a csv file (inputFilename) with all the data on a single line. Separate the
// values by commas and write each value on a separate line in a new file (outputFilename)
String data = "";
try {
for(String s :Files.readAllLines(Paths.get(inputFilename))){
s.replace(",","");
s += "\n";
data = data + s;
}
Files.write(Paths.get(outputFilename), data.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}

For-loop calculation of arbitrary times

I have a plain format txt file named enroll.txt which contains:
1997 2000
cs108 40 35
cs111 90 100
cs105 14 8
cs101 180 200
The first row shows the years of class
The second row first column shows the class name, and the following two columns show the number of students in the class in the years mentioned on the first row.
ex) In 1997, there were 40 students in class cs108.
My desired outcome: code prints as follows using
(i) split (ii) parseInt (iii) for-loop
student totals:
1997: 324
2000: 343
But this code should also work for any number of years (for example if I had student numbers for four years for each class instead of two, the code would still give me a similar output as below with student totals of say 1997, 2000, 2001, 2002 etc.)
What I have so far:
import java.util.*;
import java.io.*;
public class ProcessCourses{
public static void main(String[] args) throws FileNotFoundException{
Scanner console = new Scanner(System.in);
String fileName = console.nextLine();
Scanner input = new Scanner(new File(fileName));
while(input.hasNextLine()){
String line = input.nextLine();
String[] arr = line.split(" ");
//......????
}
}
}
What would go inside the //....????

So in the first line you have years, read them first :
Scanner input = new Scanner(new File(fileName));
String str = input.nextLine();
String[] years = str.split(" ");
Now you have set of student's information,
int[] total = new int[years.length];
while(input.hasNextLine()){
String line = input.nextLine();
String[] strength = line.split(" ");
int len = strength.length; // no of entries which includes course id + "years" no.of numbers.
for(int i=1;i<len;i++){ // from 1 because you don't care the course id
total[i-1] = total[i-1] + Integer.parseInt(strength[i]);
}
}
Then just print it :
for(int i=0;i<years.length;i++){
System.out.println(years[i]+ " : " + total[i]);
}

Cannot get values from splitted Array String into a String

I am trying to get the values out of String[] value; into String lastName;, but I get errors and it says java.lang.ArrayIndexOutOfBoundsException: 2
at arduinojava.OpenFile.openCsv(OpenFile.java:51) (lastName = value[2];). Here is my code, but I am not sure if it is going wrong at the split() or declaring the variables or getting the data into another variable.
Also I am calling input.next(); three times for ignoring first row, because otherwise of study of Field of study would also be printed out..
The rows I am trying to share are in a .csv file:
University Firstname Lastname Field of study
Karlsruhe Jerone L Software Engineering
Amsterdam Shahin S Software Engineering
Mannheim Saman K Artificial Intelligence
Furtwangen Omid K Technical Computing
Esslingen Cherelle P Technical Computing
Here's my code:
// Declare Variable
JFileChooser fileChooser = new JFileChooser();
StringBuilder sb = new StringBuilder();
// StringBuilder data = new StringBuilder();
String data = "";
int rowCounter = 0;
String delimiter = ";";
String[] value;
String lastName = "";
/**
* Opencsv csv (comma-seperated values) reader
*/
public void openCsv() throws Exception {
if (fileChooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
// Get file
File file = fileChooser.getSelectedFile();
// Create a scanner for the file
Scanner input = new Scanner(file);
// Ignore first row
input.next();
input.next();
input.next();
// Read from input
while (input.hasNext()) {
// Gets whole row
// data.append(rowCounter + " " + input.nextLine() + "\n");
data = input.nextLine();
// Split row data
value = data.split(String.valueOf(delimiter));
lastName = value[2];
rowCounter++;
System.out.println(rowCounter + " " + data + "Lastname: " + lastName);
}
input.close();
} else {
sb.append("No file was selected");
}
}

lines are separated by spaces not by semicolon as per your sample. Try in this way to split based on one or more spaces.
data.split("\\s+");
Change the delimiter as shown below:
String delimiter = "\\s+";
EDIT
The CSV file should be in this format. All the values should be enclosed inside double quotes and there should be a valid separator like comma,space,semicolon etc.
"University" "Firstname" "Lastname" "Field of study"
"Karlsruhe" "Jerone" "L" "Software Engineering"
"Amsterdam" "Shahin" "S" "Software Engineering"

Please check if you file is using delimiter as ';' if not add it and try it again, it should work!!

Use OpenCSV Library for read CSV files .Here is a detailed example on read/write CSV files using java by Viral Patel

How to find a string right after the searched string from a text file using Java?

I have text file in which I have following content.
Name Sahar Hassan
Age 26
I have wrote a Java code to find the location of the word "Name" and it works fine. I want to output the string right after the word "Name", that is "Sahar Hassan".

Keep it simple:
import java.io.*;
import java.util.Scanner;
File file = new File("somefilepath");
Scanner s = new Scanner(file);
String name = null;
while (s.hasNextLine()) {
String line = s.nextLine();
if (line.startsWith("Name"))
name = line.substring(5);
}
// The variable "name" will be the name you seek (or be null if line not found)

You could use indexOf and search for the newline character (starting from the index of Name). Like this:
String str = "Name Sahar Hassan\nAge 26";
int nameIndex = str.indexOf("Name"); // What you say you already have.
int newLineIndex = str.indexOf("\n", nameIndex);
// Extract part after "Name"
String name = str.substring(nameIndex + 5, newLineIndex);
System.out.println(name); // Prints "Sahar Hassan"