Develop Reference

Java: Using .txt files to assign specific indexes of each line to an arraylist

My .txt file is
code1,description1,price1
code2,description2,price2
etc.
Using:
ArrayList<String> items = new ArrayList<String>();
String description;
File fn = new File("file.txt");
String[] astring = new String[4];
try{
Scanner readFile = new Scanner(fn);
Scanner as = new Scanner(System.in);
while (readFile.hasNext()){
astring = readFile.nextLine().split(",");
String code = astring[0];
items.add(code);
description = astring[1];
}
}catch(FileNotFoundException){
//
}
for(String things: items){
System.out.println("The code is: " + things + "The description is " + description);
}
My output prints out
code1 description1
code2 description1
code3 description1
I'm trying to figure out how to make the description update as the code's do. e.g.
code1 description1
code2 description2
code3 description3
If this question has been asked already, I apologize. I couldn't find out how to do it by searching around but if there's a reference to figure this out I'll close this down and go there. Thanks in advance!

The problem is with your logic. You are storing only astring[0] to the items ArrayList and overwriting the value of description each time. As a result on last value read is stored in description which you are printing in the loop.
I prefer creating a custom class as follows. (Just for the sake of demo otherwise you would declare your fields as private and provide getters and setters)
class MyObject {
public String code;
public String description;
public String price;
}
now instead of creating ArrayList of Strings you will create ArrayList of MyObject as follows
ArrayList<MyObject> items = new ArrayList<MyObject>();
now create a new instance of MyObject each time you read a line , populate its fields with the values from astring as follows
ArrayList<MyObject> items = new ArrayList<MyObject>();
File fn = new File("test.txt");
String[] astring = new String[4];
try {
Scanner readFile = new Scanner(fn);
Scanner as = new Scanner(System.in);
MyObject myObject;
while (readFile.hasNext()) {
astring = readFile.nextLine().split(",");
myObject = new MyObject();
myObject.code = astring[0];
myObject.description = astring[1];
myObject.price = astring[2];
items.add(myObject);
}
} catch (Exception e) {
System.out.println(e.getMessage());
}
and then finally print it using the same foreach loop as follows
for (MyObject item : items) {
System.out.println("The code is: " + item.code + " The description is: " + item.description + " The price is: " + item.price);
}
Output
The code is: code1 The description is: description1 The price is: price1
The code is: code2 The description is: description2 The price is: price2

The reason you're seeing that output is that you are not saving description along with the code inside the list, that is why the last description is saved within the description variable not all description values.
To solve this problem, you can create a simple Java Bean/POJO class
and wrap your data inside it and then you can simply fetch the value
you have saved it and then show it properly. Take a look at the code
below:
public class Launcher{
public static void main(String[] args) {
ArrayList<Item> items = new ArrayList<Item>();
File fn = new File("file.txt");
try {
Scanner readFile = new Scanner(fn);
while (readFile.hasNext()) {
String[] astring = readFile.nextLine().split(",");
String code = astring[0];
String description = astring[1];
String price = astring[2];
Item item = new Item(code, description, price);
items.add(item);
}
} catch (FileNotFoundException d) { // }
}
for (Item thing : items) {
System.out.println(String.format("The code is: %s\tThe description is: %s\tThe Price is %s",thing.getCode(),thing.getDescription(), thing.getPrice()));
}
}
}
class Item {
private String code;
private String description;
private String price;
public Item(String code, String description, String price) {
this.code = code;
this.description = description;
this.price = price;
}
public String getCode() {
return code;
}
public String getDescription() {
return description;
}
public String getPrice() {
return price;
}
}

Map array to object

I have an array defined as follows:
String [] source = {"26", "Tom", "foo", ...};
And a Person class:
public class Person{
private String age;
private String name;
private String print;
private String ......;//the same type and order and number of source
public Person() {
}
//full construtors
public Person(String age, String name, String print,String ....) {
this.age = age;
this.name = name;
this.print = print;
//....
}
/* setters & getters */
}
How can I map these values to a Personinstance?
this is my real coding
public static List<BasicalVo> readObject(String path) throws IOException, NoSuchMethodException {
InputStreamReader fReader = new InputStreamReader(new FileInputStream(path),"gb2312");
BufferedReader bufferedReader = new BufferedReader(fReader);
String currentLine;
String[] temp;
List<BasicalVo> basicalVoList= new ArrayList<BasicalVo>();
while ((currentLine = bufferedReader.readLine()) != null) {
temp = currentLine.split(",");//I get the Array
for (int i = 0; i < temp.length; i++) {
//I don't know hot to translate to BasicalVo .
BasicalVo vo = new BasicalVo();
basicalVoList.add(vo);
}
}
return basicalVoList;
}

If the source just contains one person's data then you can do this:
Person p = new Person(source[0], source[1], source[2] ...);
If the array is too short an ArrayIndexOutOfBoundsException will be thrown.

I.
If the array contains only one Person you only need to create the instance like this :
String[] source = new String[]{"26", "tom", "xx", "....."};
Person p = new Person(source[0], source[1], source[2], source[3],...);
Because you'll know how many parameters there is in the constructor and so you won't have an ArrayIndexOutOfBoundsException if the array is well-build
II.
Assuming you have only 3 attributes, you'll be able to do like this if the array is like this :
String[] source = new String[]{"26", "tom", "xx", "22", "john", "yy"};
ArrayList<Person> list = new ArrayList<>()
for (int i = 0; i < source.length; i += 3) {
list.add(new Person(source[i], source[i + 1], source[i + 2]));
}
III.
If you have multiple fields, you would better do like this :
public Person(String[]source) {
this.age = source[0];
this.name = source[1];
this.print = source[2];
//....
}
Because it wouldn't not surcharge the code you have in your loop which read from the data, and make it easier to do your stuff, and in fact this is not hard, because in every case if you have like 20 fields, you'll have to assignate these 20 attributs
IV.
Or last proposition with a factory method :
public static Person createPersoneFromArray(String[] array) {
Person p = new Person();
p.setAge(array[0]);
p.setName(array[1]);
//...
return p;
}
And in the main method :
Person p = Person.createPersoneFromArray(source);

you can also add another constructor to your BasicalVo class which takes a String[] as input :
public BasicalVo(String [] input) {
this.age = input[0];
this.name = input[1];
this.print = input[2];
//....
}
which you then can call in your main as follows without additional for loop
....
temp = currentLine.split(",");
BasicalVo vo = new BasicalVo(temp);
basicalVoList.add(vo);
....

You can use OpenCSV
CSVReader csvReader = new CSVReader(new FileReader("people.csv"),',');
ColumnPositionMappingStrategy mappingStrategy = new ColumnPositionMappingStrategy();
mappingStrategy.setType(Person.class);
String[] columns = new String[]{"age","name","print"};
mappingStrategy.setColumnMapping(columns);
CsvToBean ctb = new CsvToBean();
List personList = ctb.parse(mappingStrategy, csvReader);

In this specific case I think that your best option is to use reflection. Reflection are a set of classes and interfaces that allow you to call different methods at execution time. For instance:
String [] source = { "26", "tom", "xx", ... };
Constructor constructor = Person.class.getConstructors()[0]
constructor.newInstance(source)
Take into account that this example only works because you have only one constructor, and so Person.class.getConstructors()[0] returns the constructor you want. YOu can try to get the specific constructor with Person.class.getConstructors(Class<?>...), in that case you would need to pass as a parameter an array with the type of the arguments.

Java Convert List<String> to List<Object>

I've two classess CsvRead and MyOwnClass.
In CsvRead I've a method public static List getDataFromCsv(); It returns list of all data. And this data I want to take in another method in class MyOwnClass and return there as list of objects of My OwnClass
It looks like this:
List<String> dataFromCsv = new ArrayList<String>();
And in another class, I want to convert it to List<Object> of my class.
private static List<String> getDataFromCsvClass = new ArrayList<String>();
getDataFromCsvClass = CsvReader.getAllCsvData(filename);
String name = dataFromCsv[0];
String surname = dataFromCsv[1];
String birth = dataFromCsv[2];
I want to return new MyOwnClass(name, surname, birth);
MY ERROR: array required but List found: String name = allData[0]; etc

You can create a method to convert a String to MyOwnClass and use stream to map the elements, e.g.:
public static MyOwnClass convertToObject(String element){
String[] tokens = element.split(",");
return new MyOwnClass(tokens[0], tokens[1], tokens[2]);
}
//code to convert
List<String> dataFromCsv = new ArrayList<String>();
List<MyOwnClass> list = dataFromCsv.stream()
.map(e -> convertToObject(e))
.collect(Collectors.toList());
However, this may not work if let's say name or surname contains comma. In which case, I would recommend having a look at OpenCSV library and this example of how to read csv into objects.

Supposing that the list contains the name, surname and birth in every group of 3 strings (i.e., the elements on index 0, 3, 6, 9 etc. contain the name), you might try the following:
public List<MyOwnClass> convertCsvData(List<String> csv_data)
{
// Initialize result
List<MyOwnClass> result;
result = new ArrayList<MyOwnClass>();
// Parse data
int counter;
String name;
String surname;
String birth;
for (counter = 0; counter < csv_data.size(); counter += 3)
{
name = csv_data.get(counter);
surname = csv_data.get(counter + 1);
birth = csv_data.get(counter + 2);
result.add(new MyOwnClass(name, surname, birth));
}
// Done
return (result);
} // convertCsvData

Somthing like this :
private static MyOwnClass toMyOwnClass(String str){
String[] object= str.split(",");
return new MyOwnClass(object[0], object[1], object[2]);
}
List<String> dataFromCsv = new ArrayList<String>();
List<MyOwnClass> list = new ArrayList<>();
for(String string : dataFromCsv ){
if(StringUtils.isNoneEmpty(string)){
list.add(toMyOwnClass(string));
}
}
And then you return your list

Java HashMap, One key multiple Values, One map

As the question reads.... and I do NOT want to use multiple maps, just one map.
My goal is to get a list of the names I enter in the input.
I have tried like a hundred different for-loops, but I always tend to end up with a list of the whole map and/or that the duplicate key is overridden.
import java.util.*;
public class Another {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String name;
HashMap<String, ToA>wordkey = new HashMap<String, ToA>();
ToA a = new ToA("Doolin", "Bill", "18580824-1464");
ToA b = new ToA("Dalton", "Bob", "18701005-2232");
ToA c = new ToA("James", "Jesse", "18470905-2401");
ToA d = new ToA("Dalton", "Emmet", "18710713-0818");
wordkey.put("Doolin", a);
wordkey.put("Dalton", b);
wordkey.put("James", c);
wordkey.put("Dalton", d);
System.out.println("Efternamn:");
name = scan.next();
}
}
public class ToA{
private String fname, lname, dob;
public ToA(String fname, String lname, String dob){
this.fname = fname;
this.lname = lname;
this.dob = dob;
}
public String getFname(){
return fname;
}
public String getLname(){
return lname;
}
public String getDob(){
return dob;
}
public String toString(){
return "\nFirstname: " + fname + "\nSurname: " + lname + "\nDateOfBirth: " + dob;
}
}
For inputting Dalton, I would like the output
Firstname: Bill
Surname: Dalton
DateOfBirth: 18701005-2232
Firstname: Emmet
Surname: Dalton
DateOfBirth: 18710713-0818
I'm really stuck with this so any help is highly appreciated, Thanks

To post my comment as an answer: use a Map<String, List<ToA>> like this:
Map<String, List<ToA>> wordkey = new HashMap<>();
ToA a = new ToA("Doolin", "Bill", "18580824-1464");
ToA b = new ToA("Dalton", "Bob", "18701005-2232");
ToA c = new ToA("James", "Jesse", "18470905-2401");
ToA d = new ToA("Dalton", "Emmet", "18710713-0818");
wordkey.put("Doolin", Arrays.asList(a));
wordkey.put("James", Arrays.asList(c));
wordkey.put("Dalton", Arrays.asList(b, d));
To print the names based on the input, you can do something like this:
System.out.println("Efternamn:");
name = scan.next();
List<ToA> toas = wordkey.get(name);
if (toas != null) {
System.out.println("ToAs");
for (ToA toa : toas) {
System.out.println("ToA: " + toa);
}
}
else {
System.out.println("No ToAs found for input: " + name);
}

There are several possibilities for what you are trying to achieve. A simple one would be to use Guavas Multimap or to use Apaches MultiMap.
Another possibility is to "wrap" the Map in a class and keep a List<ToA> as Value of the Map. You'd override the put, remove and get methods to what you need

Passing arrays into testclass constructors

I need to pass a 1d array that isn't defined in a method.
I need to create a testclass then make the arrays myself.
I'm just not sure about the syntax.
Example, here's my company class:
public class Company
{
String name;
String address;
Employee employeeList[] = new Employee[3];
public Company (String name, String address ,
Employee employeeList, String jobTitle )
{
this.name = name;
this.address = address;
}
public void printDetails()
{
for(int i = 0; i>employeeList.length;i++)
{
System.out.println(" The companys name is " + name);
System.out.println(" The Companys Address is "+ address);
System.out.println("The List of employees are " + employeeList[i].name);
System.out.println("The Titles of These Employees are " + employeeList[i].jobTitle);
}
}
}
But my testclass is where the problem lies.
Where do I go from here? Do do I put arrays(employees) into it?
public class TestCompany
{
public static void main(String[] args)
{ employees?
Company hungryBear = new Company("hungryBear ", "Those weird apartments ",////// );
}
}

public Company (String name, String address ,
Employee employeeList, String jobTitle )
Should be:
public Company (String name, String address ,
Employee []employeeList, String jobTitle )
Right now, you're not passing an array to your method, your passing an instance. You need to tell Java that you're passing an array.
Editted with new knowledge of the employee class...
Also, you will need to build the array in your main function before you pass it. Something like this:
public static void main(String[] args){
Employee [] employeeList = {
new Employee("Samuel T. Anders", "Player, Caprica Buccaneers"),
new Employee("William Adama", "Commander, Battlestar Galactica")
};
Company hungryBear = new Company("hungryBear ", "Those weird apartments ", employeeList);
}
Not really sure this answers your question, but maybe this will help you with the syntax of array passing a little.
Another edit, another way to initialize an array:
Empolyee [] employeeList = new Employee[2];
employeeList[0] = new Employee("Samuel T. Anders", "Player, Caprica Buccaneers");
employeeList[1] = new Employee("William Adama", "Commander, Battlestar Galactica");

Empolyee [] employeeList = new Employee[2];
for(int i=0;i<2;i++){
Scanner input = new Scanner(System.in);
employeeList[i] = input.next();
}