Java, using Scanner to fetch data line by line

Question

I'm basically running this code:

AddressBook.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package addressbook;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

/**
 *
 * @author hassan
 */
public class AddressBook extends Application {

    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("MainWindow.fxml"));

        Scene scene = new Scene(root);

        stage.setScene(scene);
        stage.setResizable(false);
        stage.show();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
        new AddressBookMapper().parseDataFile();
    }
}

AddressBookMapper.java:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package addressbook;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Pattern;
/**
 *
 * @author hassan
 */
public class AddressBookMapper {
    private File dataFile;
    private FileWriter fileWriter;
    private PrintWriter printWriter;
    public ArrayList lines;

    private void openDataFile() {
        this.dataFile = new File("src/addressbook/datafile.txt");
    }
    public void writeData() {

        System.out.println(this.lines);
        Iterator iterator = this.lines.iterator();
        System.out.println(this.lines.get(0));
        while(iterator.hasNext()) {
            System.out.println();
            System.out.println("-----");
        }
    }
    public void createAddress(String fullName, String email, String telephoneNumber, String mobileNumber) {
        this.openDataFile();
        try {
            this.fileWriter = new FileWriter(this.dataFile, true);
            this.printWriter = new PrintWriter(this.fileWriter);
            this.printWriter.append(fullName + "," + email + "," + telephoneNumber + "," + mobileNumber + "\n");
            this.printWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public int getLastId() {
        return 0;
    }
public void parseDataFile() {
    File dataFile = new File("src/addressbook/datafile.txt");

    try {
        Scanner scanner = new Scanner(dataFile, "UTF-8").useDelimiter("\\n");

        while(scanner.hasNext()) {
            System.out.println(scanner.next());
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    this.writeData();
}
    private int findLastAddressId() {
        return 0;
    }
}

My data file text:

ff,ff,fff,ff
krfr,frffr,frfs,ff
a,a,b,c
d,a,f,e
fa,e,f,a

But, for some reason, I get this output:

ff,ff,fff,ff
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
krfr,frffr,frfs,ff
a,a,b,c
d,a,f,e
fa,e,f,a
null
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.NullPointerException
    at addressbook.AddressBookMapper.writeData(AddressBookMapper.java:36)
    at addressbook.AddressBookMapper.parseDataFile(AddressBookMapper.java:69)
    at addressbook.AddressBook.main(AddressBook.java:36)
    ... 11 more
Exception running application addressbook.AddressBook
Java Result: 1

Any solution? I am basically trying to get the text from my data file line by line and stack it up into my ArrayList. Also, when writing my datafile adds a blank line in the end of the document.

It's hard to understand purpose of "this.openDataFile();" and "this.dataFile" — Kartic, Apr 25 '15 at 18:35
What's at AddressBookMapper.java line 69? And don't use `==` with `String` — , Apr 25 '15 at 18:53
so `this.lines` is `null`. And yes `equals` for `String` (As a side note, you might want to use [`Files#readAllLines`](http://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#readAllLines(java.nio.file.Path,%20java.nio.charset.Charset))) here — , Apr 25 '15 at 18:56
Common, can't you google it? (here you go: http://www.java2s.com/Tutorials/Java/java.nio.file/Files/Java_Files_readAllLines_Path_path_Charset_cs_.htm) — , Apr 25 '15 at 19:00
Something smells fishy. The NPE seems to be a red herring. With properly instantiated elements, the only exception I get is `NoSuchElementException` which is what I expected. — Makoto, Apr 25 '15 at 19:14
@RC. It did output everything but with a `null` and loads of errors. http://pastebin.com/205kpKLL — Hassan, Apr 25 '15 at 19:14
Please no - that's not necessary. All I really care to see is where `lines` is instantiated. — Makoto, Apr 25 '15 at 19:16
@Kartic I did but it did not work. I did try your answer with `this.` prefixed — Hassan, Apr 25 '15 at 19:19
I tried a new method which @RC. suggested. It works better but with a few errors that need to be patched — Hassan, Apr 25 '15 at 19:20

Kartic · Answer 1 · 2015-04-25T19:20:37.103

1

Can you please try -

while(scanner.hasNext()) {
    lines.add(scanner.next());
}

edited Apr 25 '15 at 19:20

answered Apr 25 '15 at 19:02

Kartic

2,575
5
19
39

Let me get a pastebin – Hassan Apr 25 '15 at 19:06
http://pastebin.com/DGXRTVJz – Hassan Apr 25 '15 at 19:06
This is actually the correct response. It'd be great if you came back and justified it a bit more. – Makoto Apr 25 '15 at 19:16

Java, using Scanner to fetch data line by line

1 Answers1