I have a class defined like this, with the appropriate getter and setter methods...
public class Album {
private int id;
private String artist;
private String name;
private int published;
}
I also have a .csv file that stores this content for a number of Albums. In the file, one line represents one Album.
I'm trying to read the information from the .csv file, and then use the setters of the Album class to assign the values. Here is my code...
public Map<Integer, Album> load() {
Scanner scanner = new Scanner(fileName);
Map<Integer, Album> loadedAlbums = new HashMap<Integer, Album>();
while(scanner.hasNextLine()) {
Album album = new Album();
String[] albumDivided = scanner.nextLine().split(",");
//in the .csv file every unit of information is divided by a comma.
album.setId(Integer.parseInt(albumDivided[0])); //this is line 11.
album.setArtist(albumDivided[1]);
album.setName(albumDivided[2]);
album.setPublished(Integer.parseInt(albumDivided[3]));
loadedAlbums.put(album.getId(), album);
}
return loadedAlbums;
}
However, trying to use this code, I get the following Exception:
java.lang.NumberFormatException: For input string: "albums.csv" at line 11.
Could you please help me to understand the cause of this problem.
Well the problem is described to you by the Exception...
A NumberFormatException would have been triggered by one of your Integer.parseInt() lines. The line of your code that is triggering the exception is Line 11 (as per the exception message) - not sure which one this is but its probably the first Integer.parseInt() line.
Your code is trying to convert the value "albums.csv" to a number, which is obviously isn't. So somewhere in your CSV file you must have a line that contains the value albums.csv where it is expecting a number.
Hope this helps pinpoint the problem.
Since you don't want the whole solution here is a hint to resolve your problem:
You should take a look at the API documentation of the Scanner class. Take a really close look on the constructor that expects a single String parameter (as you use it in your code).
As far as I can tell, albumDivided[0] will containt "1." which will not be able to parse to an integer because of the dot. Either remove the dot from your csv file, or create a new string that removes the dot before you parse it to Integer. The approach might look something like this:
String newString;
for(int i=0;i<albumDivided[0].length-1;i++){ //length -1 to remove the dot
newString = newString + albumDivided[0].charAt(i); //get the string stored in albumDivided[0] and add each char to the new string
}
Related
I Have a formatted text file called cars.txt; It's separated by tabs.
Name Length Width
truck1 18.6 8.1
suv1 17.4 7.4
coupe1 14.8 5.4
mini1 14.1 5.0
sedan1 16.4 6.1
suv2 17.5 7.3
mini2 14.3 5.2
sedan2 16.5 6.2
I need to read in this information so it can be used for calculations later on.
This is my current idea but I am having a hard time piecing together what I need to execute.
public class Class{
public void readFileIn(){
Scanner sc = new Scanner(new FileReader("cars.txt");
try{
while (sc.hasNextLine()){
if (/**something that catches strings*/){
method1(string1, double1, double2);
method2(double1, double2);
}
}
}catch(FileNotFoundException exception){
System.out.println("File dosen't exist");
}
}
}
Scanner and Buffer Reader are not used very often anymore as Java provides a better way to achieve tha same result with less code.
I can see at least three possible approaches to solve your problem:
approach 1: if you can use at least Java 8, then I would suggest to use the java.nio.file libraries to read the file as a stream of lines:
Stream<String> linesStream=Files.lines("cars.txt");
Then depending on what you need to do, you could use either forEach that will loop on each line of the stream:
linesStream.forEach(e -> e.myMethod());
Or Java Collectors to execute the calculation that you need to. A good tutorial about Collectors can be found here. You can use collectors also to separate your string etc...
approach 2: you can use Apache Commons libraries to achieve the same goal. In particular you could use FileUtils and StringUtils. For instance:
File carFile=new File("cars.txt");
LineIterator lineIterator=lineIterator(carFile);
for(String line : lineIterator) {
String[] my values=StringUtils.split(line);
//do whatever you need
}
approach 3: use Jackson to transform your file into a json or a java object that you can then use for your own transformations. Here is an example explaining how to convert a CSV to JSON. With a bit of digging in the Jackson documentation, you could apply it to your case.
First of all, i recommend you create an Entry class that represents your data.
private class Entry {
private String name;
private double length;
private double width;
// getters and setters omitted
#Override
public String toString() {
// omitted
}
}
Next, create a method that takes a String as an arguments and is responsible for parsing a line of text to an instance of Entry. The regex \\s+ matches any whitespace characters and will split your line to its individual columns. Remember that in production, Double.valueOf can throw an RuntimeException if your are not passing a valid String.
Finally, you can read the file, here using the Java 8 stream API. Skip the first line since it includes the column header and not actual data.
private void readFile() throws Exception {
Path path = Paths.get(/* path to your file */);
Files.readAllLines(path).stream().skip(1).map(FileReadTest::toEntry)
.forEach(this::action);
}
In my example, i am just printing each entry to the console:
private void action(Entry entry) {
System.out.println(entry);
}
Resulting output:
Entry[name='truck1', length=18.6, width=8.1]
Entry[name='suv1', length=17.4, width=7.4]
Entry[name='coupe1', length=14.8, width=5.4]
Entry[name='mini1', length=14.1, width=5.0]
Entry[name='sedan1', length=16.4, width=6.1]
Entry[name='suv2', length=17.5, width=7.3]
Entry[name='mini2', length=14.3, width=5.2]
Entry[name='sedan2', length=16.5, width=6.2]
Here's an example of how to properly read a text file - replace the charset with the one you need.
try (final BufferedReader br = Files.newBufferedReader(file.toPath(), StandardCharsets.UTF_8)) {
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
Once you have the individual lines, you can split them by whitespace: str.split("\\s+");
You get an array with three entries. I guess you can figure out the rest.
I am trying to create a public instance method that takes no arguments and returns no values. It is required to get an input from a user to select a file, this part I have no issues with. The method needs to make use of the BufferReader and Scanner Objects. So that it can read the file selected. For each line that is read, a new object should be created and its instance variables set using the values found in the file.
That object that is created should then be added to a list. This is where I am having issues, it won't let me add the new object to the list. Below is my code:
public void readInEntrants()
{
String pathname = OUFileChooser.getFilename();
File aFile = new File(pathname);
Scanner bufferedScanner = null;
Set<Entrant> entrantSet = new HashSet<>();
try
{
String currentEntrantLine;
Scanner lineScanner;
bufferedScanner = new Scanner(new BufferedReader(new FileReader(aFile)));
while (bufferedScanner.hasNextLine())
{
currentEntrantLine = bufferedScanner.nextLine();
lineScanner = new Scanner(currentEntrantLine);
lineScanner.useDelimiter(" ");
currentEntrantLine = lineScanner.next();
entrantSet.add(new Entrant(currentEntrantLine)); // <----- Here is where I am having trouble. It won't let me add the new object to the class Entrant
}
}
catch (Exception anException)
{
System.out.println("Error: " + anException);
}
finally
{
try
{
bufferedScanner.close();
}
catch (Exception anException)
{
System.out.println("Error: " + anException);
}
}
return entrantSet;
}
I'm not sure what to do. Could anyone see what I am doing wrong?
Sorry for got to add that it is a compilation issue, it will not compile properly.
Use an IDE ,I bet you dont (otherwise it would mark compilation error immediatly with red -> you use return in void method ) and in this case you would see other errors.
(off: this would go to comment section however under 50reputation I am not allowed to do that. Stackoverflow should change this imo. )
First of all:
You marked function readInEntrants as public void so you can't use return inside.
You could either remove return entrantSet; instruction or change function definition to public Set<Entrant> readInEntrants.
Concerning problem you have:
Basing on comment you left on beatrice answer I think you have only parameterless constructor for 'Entrant' class, while you try to create it passing string as parameter.
new Entrant(currentEntrantLine)
What you need to do is define Entrant class constructor that accept String as it's argument. For example:
public Entrant(String dataToParse)
{
// here you parse data from string to entrant fields
}
On the side:
You use bufferedReader to read entire file line at once and that's ok, but then you define Scanner lineScanner to iterate through line elements and then use it only once.
This way for file... let's say:
One Two Three
Four Five Six
Your while loop would work like this:
Store "One Two Three" inside currentEntrantLine.
Create scanner that'll work on "One Two Three", and set it to use space as delimiter.
Use .next to "Finds and returns the next complete token" (see documentation) and then store value inside currentEntrantLine. This way contents of currentEntrantLine is "One". Not entire line.
In next iteration you would have scanner working on "Four Five Six" and "Four" as currentEntranceLine content.
It seems the constructor of entrant class does not have any argument. Pass String as an argument type in the constructor to set the String field inside the Entrant class .
I have this code, and the string is coming from JSON from the server, and I use these if statements to prioritize what I want to get exported to the text file, but when I run it, the output isnt the output I am expecting, see below:
JSONObject attributeObject = objects.getJSONObject(objectAttribute);
String[] elementList = JSONObject.getNames(attributeObject);
for (String attributeName : elementList) {
if (attribute.equals("Custodian")){
String value = objects.getString("attributeValue");
System.out.print(value+",");
out.write(value);
out.append(",");
}
if (attribute.equals("Custodian Delegate")){
String value = objects.getString("attributeValue");
System.out.print(value+",");
out.write(value);
out.append(",");
}
if (attribute.equals("Authentication Directory")){
String value = objects.getString("attributeValue");
System.out.print(value+",");
out.write(value);
out.append(",");
}
if (attribute.equals("User ID")){
String value = objects.getString("attributeValue");
System.out.println(value);
out.write(value);
out.append(",");
out.newLine();
}
}
Expected output based from the if statements:
JDoe,CPer,Active Directory, No
But once I run it, the output becomes:
Active Directory,JDoe,CPer,No
Is there an easier way to fix this? My only problem is that the Authentication Directory goes first when I start running the program. Any tips? I would greatly appreciate.
Thanks in advance
make your life easy by creating a Model class
class Model{
String JDoe=""; //this is an example, so change attribute names using naming convention
String CPer="";
String Active_Directory="";
String No="";
#Override
public String toString(){
return JDoe+", " +CPer+", " +Active_Directory+", " + No;
}
}
now change your code to use this model, and only update the class Model without writing anything to the file.
for example:
Model model = new Model();
...
for(whatever condition is){ //start of the loop
if (attribute.equals("Custodian")){
String value = objects.getString("attributeValue");
model.CPer=value;
//System.out.print(value+",");
//out.write(value); <-- skip this
//out.append(","); <-- skip this
}
...
}
//after the loop
out.write(model.toString());
NOTE:
if you have two loops place Model model = new Model();
inside your outter loop
The output might be correct. You are iterating over all keys of the JSON-object. The resulting order does not depend on the order of your if-satements. In every loop only a single if-condition matches. The given snippet will output the elements in the same order as in the returned array.
The .getNames() returnes the array of the field names of the given Object. Then you are iterating over theses field names. Therfore the attribute value will have the same value per cycle. It is impossible that two if-condition will match because attribute can not equal for example "Custodian" and "Custodian Delegate" at thes same time.
It seems like the array contains the attributes in an alphabetic order. Therefore the attributeName-variable is "Authentication Directory" during the first cycle.
I have a CSV file which has only one column with 100+ rows. I would like to put those values in an one dimensional array(only if its possible). So that it works as same as if I wrote a string array manually. I.e.
String[] username = {'lalala', 'tatata', 'mamama'}; //<---if I did it manually
String[] username = {after passing the CSV values}; //<---I want this like the above ones.
Then later I would like to be able to initialized that class to a different class, say if the class that holds the array is called ArrayClass, I would like to be able to initialized this to different class, like this --
public class MainClass{
ArrayClass array = new ArrayClass();
//Then I would like to be able to do this
someMethod(array.username);
}
I know I asked a lot of things but I seriously appreciate all your help. Even if you see this question and say THIS IS BS. Oh and one more thing I would prefer it to be in JAVA.
It might be easier to use an arraylist rather than an array as you dont have to worry about number of rows. An array has a fixed size that cant be changed. i.e ArrayList
As you have only one column you will not need to worry about commas in csv
Example code would look something like this:
import java.util.*;
import java.io.*;
public class MyClass {
private ArrayList<String> MyArray = new ArrayList<String>();
private Scanner scan;
public MyClass(){
try {
scan = new Scanner(new File("MyFile.csv"));
} catch (IOException ioex) {
System.out.println("File Not Found");
}
}
public ArrayList<String> getArray() {
while (scan.hasNext()) {
Scanner line = new Scanner(scan.nextLine());
MyArray.add(line.next());
}
return MyArray;
}
}
And in the main:
MyClass f = new MyClass();
System.out.println(f.getArray());
If it's just a csv you can use the split method of string with a proper regex.
Please do check the split method
The first half of your question is easy and can be handled in a number of different ways. Personally, I would use the Scanner class and set the delimiter to be ",". Create a new Scanner Object and then call setDelimiter(",") on it. Then simply scan through the tokens. See the example on the documentation. This method of doing things is effective because it handles reading in the file and separating it based on your criteria (the ',' character).
Hi I keep getting the following error:
The method setOfficeCode(String) in the type UnitForm is not applicable for the arguments (List<String>)
The java code I have is:
public static void main(String[] args)
{
UnitForm uform = (UnitForm) form;
List<String> lines = new ArrayList<String>();
lines.add("Once upon a midnight dreary");
lines.add("While I pondered weak and weary");
lines.add("Over many a quaint and curious volume of forgotten lore");
String[] linesArr = lines.toArray(new String[lines.size()]);
for (String line : linesArr)
{
System.out.println(line);
}
uform.setOfficeCode(lines);
}
I am trying to output what is contained in lines to a formbean in my jsp and if I convert setOfficeCode to a list what i see on my jsp is coming out with [] around it like [Over many a quaint and curious volume of forgotten lore, Hi, Bye] and I don't want the brackets to appear around the data on the jsp and i would like to break them up into separate lines instead of a whole string so that hi is on a new line and bye is on a new line etc.
Your setOfficeCode expects a String as parameter and your giving it a list of Strings. Either change the setOfficeCode definition so it accepts a list, or pass only one String from your list at the method call.
Plus you don't need the array conversion as you can also do:
for (String line : lines)
{
System.out.println(line);
}
setOfficeCode{String input)
is not equal to
setOfficeCode(List input).
The error tells you exactly and explicitly what is wrong.
So, you problem is actually one of not understanding how your code works.
What you need to do is prepare your data before you output it in proper HTML format, or modify your JSP to handle the list instead of just a string.
Simplest way to do this would use commons-lang library (which is likely already in your class path) and do something like:
uform.setOfficeCode(StringUtils.join(lines, "<br/>"));