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;
}
}

manipulate and sort text file

I am working on a project where I have been given a text file and I have to add up the points for each team and printout the top 5 teams.
The text file looks like this:
FRAMae Berenice MEITE 455.455<br>
CHNKexin ZHANG 454.584<br>
UKRNatalia POPOVA 453.443<br>
GERNathalie WEINZIERL 452.162<br>
RUSEvgeny PLYUSHCHENKO 191.399<br>
CANPatrick CHAN 189.718<br>
CHNHan YAN 185.527<br>
CHNCheng & Hao 271.018<br>
ITAStefania & Ondrej 270.317<br>
USAMarissa & Simon 264.256<br>
GERMaylin & Daniel 260.825<br>
FRAFlorent AMODIO 179.936<br>
GERPeter LIEBERS 179.615<br>
JPNYuzuru HANYU 197.9810<br>
USAJeremy ABBOTT 165.654<br>
UKRYakov GODOROZHA 160.513<br>
GBRMatthew PARR 157.402<br>
ITAPaul Bonifacio PARKINSON 153.941<br>
RUSTatiana & Maxim 283.7910<br>
CANMeagan & Eric 273.109<br>
FRAVanessa & Morgan 257.454<br>
JPNNarumi & Ryuichi 246.563<br>
JPNCathy & Chris 352.003<br>
UKRSiobhan & Dmitri 349.192<br>
CHNXintong &Xun 347.881<br>
RUSYulia LIPNITSKAYA 472.9010<br>
ITACarolina KOSTNER 470.849<br>
JPNMao ASADA 464.078<br>
UKRJulia & Yuri 246.342<br>
GBRStacey & David 244.701<br>
USAMeryl &Charlie 375.9810<br>
CANTessa & Scott 372.989<br>
RUSEkaterina & Dmitri 370.278<br>
FRANathalie & Fabian 369.157<br>
ITAAnna & Luca 364.926<br>
GERNelli & Alexander 358.045<br>
GBRPenny & Nicholas 352.934<br>
USAAshley WAGNER 463.107<br>
CANKaetlyn OSMOND 462.546<br>
GBRJenna MCCORKELL 450.091<br>
The first three letters represent the team.
the rest of the text is the the competitors name.
The last digit is the score the competitor recived.
Code so far:
import java.util.Arrays;
public class project2 {
public static void main(String[] args) {
// TODO Auto-generated method stub
String[] array = new String[41];
String[] info = new String[41];
String[] stats = new String[41];
String[] team = new String[41];
//.txt file location
FileInput fileIn = new FileInput();
fileIn.openFile("C:\\Users\\O\\Desktop\\turn in\\team.txt");
// txt file to array
int i = 0;
String line = fileIn.readLine();
array[i] = line;
i++;
while (line != null) {
line = fileIn.readLine();
array[i] = line;
i++;
}
//Splitting up Info/team/score into seprate arrays
for (int j = 0; j < 40; j++) {
team[j] = array[j].substring(0, 3).trim();
info[j] = array[j].substring(3, 30).trim();
stats[j] = array[j].substring(36).trim();
}
// Random stuff i have been trying
System.out.println(team[1]);
System.out.println(info[1]);
System.out.println(stats[1]);
MyObject ob = new MyObject();
ob.setText(info[0]);
ob.setNumber(7, 23);
ob.setNumber(3, 456);
System.out.println("Text is " + ob.getText() + " and number 3 is " + ob.getNumber(7));
}
}
I'm pretty much stuck at this point because I am not sure how to add each teams score together.

This looks like homework... First of all you need to examine how you are parsing the strings in the file.
You're saying: the first 3 characters are the country, which looks correct, but then you set the info to the 4th through the 30th characters, which isn't correct. You need to dynamically figure out where that ends and the score begins. There is a space between the "info" and the "stats," knowing that you could use String's indexOf function. (http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf(int))

Have a look at Maps.
A map is a collection that allows you to get data associated with a key in a very short time.
You can create a Map where the key is a country name, with value being the total points.
example:
Map<String,Integer> totalScore = new HashMap<>();
if (totalScore.containsKey("COUNTRYNAME"))
totalScore.put("COUNTRYNAME", totalScore.get("COUNTRYNAME") + playerScore)
else
totalScore.put("COUNTRYNAME",0)
This will add to the country score if the score exists, otherwise it will create a new totalScore for a country initialized to 0.

Not tested, but should give you some ideas:
public static void main(String... args)
throws Exception {
class Structure implements Comparable<Structure> {
private String team;
private String name;
private Double score;
public Structure(String team, String name, Double score) {
this.team = team;
this.name = name;
this.score = score;
}
public String getTeam() {
return team;
}
public String getName() {
return name;
}
public Double getScore() {
return score;
}
#Override
public int compareTo(Structure o) {
return this.score.compareTo(o.score);
}
}
File file = new File("path to your file");
List<String> lines = Files.readAllLines(Paths.get(file.toURI()), StandardCharsets.UTF_8);
Pattern p = Pattern.compile("(\\d+(?:\\.\\d+))");
List<Structure> structures = new ArrayList<Structure>();
for (String line : lines) {
Matcher m = p.matcher(line);
while (m.find()) {
String number = m.group(1);
String text = line.substring(0, line.indexOf(number) - 1);
double d = Double.parseDouble(number);
String team = text.substring(0, 3);
String name = text.substring(3, text.length());
structures.add(new Structure(team, name, d));
}
}
Collections.sort(structures);
List<Structure> topFive = structures.subList(0, 5);
for (Structure structure : topFive) {
System.out.println("Team: " + structure.getTeam());
System.out.println("Name: " + structure.getName());
System.out.println("Score: " + structure.getScore());
}
}
Just remove <br> from your file.

Loading file into memory
Your string splitting logic looks fine.
Create a class like PlayerData. Create one instance of that class for each row and set all the three fields into that using setters.
Keep adding the PlayerData objects into an array list.
Accumulating
Loop through the arraylist and accumulate the team scores into a hashmap. Create a Map to accumulate the team scores by mapping teamCode to totalScore.
Always store row data in a custom object for each row. String[] for each column is not a good way of holding data in general.

Take a look in File Utils. After that you can extract the content from last space character using String Utils e removing the <br> using it as a key for a TreeMap. Than you can have your itens ordered.
List<String> lines = FileUtils.readLines(yourFile);
Map<String, String> ordered = new TreeMap<>();
for (String s : lines) {
String[] split = s.split(" ");
String name = split[0].trim();
String rate = splt[1].trim().substring(0, key.length - 4);
ordered.put(rate, name);
}
Collection<String> rates = ordered.values(); //names ordered by rate
Of course that you need to adjust the snippet.

How do you send an array to an arraylist?

I am have trouble creating an array or object(with multiple fields) and sending it to an array-list. Any help would be greatly appreciated. I have spent hours looking through every video on YouTube with the words object and array-list in them and have been unable to find much help.
The program needs to prompt the user to pick a option (1. AddItem) then prompt the user for the name and format (dvd, vhs) and save multiple objects with these variables in an array-list. I either keep having the location where it is saved in memory returned to me or instead of multiple objects one large object is created.
Library:
import java.util.Scanner;
import java.util.ArrayList;
public class Library {
static ArrayList<Object> items = new ArrayList<Object>();
static int menuOption;
static Scanner scan = new Scanner(System.in);
public static void main(String args[]) {
String title, format;
boolean right = false;
do{
displayMenu();
if (menuOption == 1){
System.out.println("Enter Title: ");
title = scan.next();
System.out.println("Enter format: ");
format = scan.next();
addNewItem(title, format);
} else {System.out.println(items);
}
} while (!right);
}
static int displayMenu(){
System.out.println("Menu: ");
System.out.println("1. Add New Item");
menuOption = scan.nextInt();
return menuOption;
}
static void addNewItem(String title, String format){
MediaItem b = new MediaItem();
b.setTitle(title);
b.setFormat(format);
items.add(b);
}
}
MediaItem:
public class MediaItem {
String title;
String format;
MediaItem(){
title = null;
format = null
}
MediaItem(String title, String format){
title = new String();
format = new String();
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getFormat() {
return format;
}
public void setFormat(String format) {
this.format = format;
}
}

The program will run if you:
1 - Change the line
static ArrayList<Object> items = new ArrayList<Object>();
to
static ArrayList<MediaItem> items = new ArrayList<MediaItem>();
2 - Change the line
System.out.println( items );
to
for ( MediaItem mi : items )
{
System.out.println( mi.getTitle() + ", " + mi.getFormat() );
}
3 - Insert a ";" at the end of the line
format = null
I did it here and it worked.

I either keep having the location where it is saved in memory returned to me
I am guessing you ran into this when you tried to either use System.out.println() to print a MediaItem, or you otherwise tried to automatically convert an object to a string. Whatever approach you took when you were seeing the memory addresses is probably the right way to do it, your problem was only in your displaying of the data.
Consider:
MediaItem item = ...;
System.out.println(item);
By default, Java doesn't know how to convert arbitrary objects to strings when you do stuff like that, and so it just spits out the class name and memory address. You either need to print the fields separately (e.g. Java knows how to display a String already), like:
System.out.println("Title: " + item.getTitle() + " Format: " + item.getFormat());
Or you can override toString() (declared in Object) to provide a custom string conversion:
class MediaItem {
...
#Override public String toString () {
return "Title: " + title + " Format: " + format;
}
}
And then you can print it directly:
System.out.println(item);
It is the default base implementation of Object.toString() that produces those strings with the memory address in them.
Based on your description, I'm guessing you had a roughly working implementation but ran into this issue and ended up changing around (and breaking) a bunch of other unrelated things to try and fix it.

Storing objects in a database java

So I'm working on a program to interface with a file based database. Mostly I'm trying to figure out how to work with it so that I can make objects and store their information in the database so that I can pull the data later.
IE Object Taylor
Name = Taylor
Age = 20
School = Whatever
So that I can get back on and call that information up when queried.
This is an example of an object I want to store. I may be doing this part wrong.
package com.catalyse.db;
public class Taylor implements java.io.Serializable
{
public String name = "Taylor M May";
public int age = 20;
public String school = "UC Boulder";
}
The DB structure I'm using is based on RandomAccessFile and I didn't make it, I'm just trying to figure out how to implement it.
package com.catalyse.db;
import java.util.*;
import java.util.Scanner;
/**
* Simple test class for the RecordsFile example. To run the test,
* set you CLASSPATH and then type "java hamner.dbtest.TestRecords"
*/
public class Run {
static void log(String s) {
System.out.println(s);
}
private static String name()
{
Scanner name = new Scanner(System.in);
String name1 = name.next();
return name1;
}
public static void main (String[] args) throws Exception {
System.out.println(new Date());
Scanner SC = new Scanner(System.in);
log("What would you like to name the database?");
String filename = SC.next();
log("creating records file...");
RecordsFile recordsFile = new RecordsFile(filename+".records", 64);
log("adding a record...");
RecordWriter rw = new RecordWriter("foo.username");
rw.writeObject(new Taylor());
recordsFile.insertRecord(rw);
log("reading record...");
RecordReader rr = recordsFile.readRecord("foo.username");
Taylor name = (Taylor)rr.readObject();
System.out.println("\tlast access was at: " + name.toString());
log("test completed.");
}
}
And here is what I get back from it,
Wed Nov 20 11:56:04 MST 2013
What would you like to name the database?
save3
creating records file...
adding a record...
reading record...
last access was at: com.catalyse.db.Taylor#50aed564
test completed.
My problem is that I want it to return information about the class, not just its name and location in the DB.

You need to override the toString method.
public String toString()
{
StringBuilder sb = new StringBuilder();
sb.append("Name: ");
sb.append(this.name);
//rest of fields
return sb.toString();
}
As a matter of clarity, you are not returning its location in the database. You are getting back the object hashValue + the class name.

At this point
Taylor name = (Taylor)rr.readObject();
You can access whatever information you like in the object, e.g.
Taylor name = (Taylor)rr.readObject();
System.out.println(name.age + ", " + name.name + ", " + name.school);
Alternatively, just add a
public String toString()
{
return name + ", " + age + ", " + school;
}
method in Taylor and then output it like so
Taylor name = (Taylor)rr.readObject();
System.out.println(name);
Now, concerning...
System.out.println("\tlast access was at: " + name.toString());
name.toString() isn't really required. If you append an object to a String then it automatically calls that objects toString() method to get a value.
Lastly, I'd like to note that generally we don't access object members like name, school and age by just accessing them. We generally make them private members then add methods to get and set them, so that we control and can track how they are manipulated.

Java / from string to java code

I have some value which I get in string format from a file.
For example, in the File A I have:
id = 342
name = Jonatan
country = USA
In addition, I have class: person with the next fields:
String id;
String name;
String country;
String grades;
String location;
and I have getter and setter for all the fields.
Now, I want to create a new instance of person, which represents Jonatan.
But - I don't want to update all the field, only the fields I need.
So, what I want to do is the next: get the details from the file, and then for every one do set, and update the correct value. For example, setName(Jonatan). The problems is that my name is in a String format. so I cant do setName - because name is in a string format, and Java doesn't give me the option of call a method in a string format.
There is easy way to it?

You might have a look at Apache BeanUtils
The application is pretty simple - to call setId("42") of a person call:
PropertyUtils.setSimpleProperty(person, "id", "42");

I like #michael_s's answer with BeanUtils. If you want to do it without, you can write:
Person person = new Person();
Properties properties = new Properties();
properties.load(new FileInputStream("the.properties"));
for (Object key : properties.keySet()) {
String field = (String) key;
String setter = "set" + field.substring(0, 1).toUpperCase() + field.substring(1);
Method method = Person.class.getMethod(setter, String.class);
method.invoke(person, properties.get(key));
}
Not that the stream should be closed after using it, and that this short example only works for String properties.

Using java reflection you can determine what methods/fields are available.
You can use this example to pass your key/value pairs into the doReflection method to set the new values of your properties in the instance of the Bean-class.
public class Bean {
private String id = "abc";
public void setId(String s) {
id = s;
}
/**
* Find a method with the given field-name (prepend it with "set") and
* invoke it with the given new value.
*
* #param b The object to set the new value onto
* #param field The name of the field (excluding "set")
* #param newValue The new value
*/
public static void doReflection(Bean b, String field, String newValue) throws NoSuchMethodException,
SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Class<? extends Bean> c = b.getClass();
Method id = c.getMethod("set" + field, String.class);
id.invoke(b, newValue);
}
public static void main(String... args) throws NoSuchMethodException, SecurityException, IllegalArgumentException,
InvocationTargetException, IllegalAccessException {
Bean bean = new Bean();
System.out.println("ID before: " + bean.id);
doReflection(bean, "Id", "newValue");
System.out.println("ID after: " + bean.id);
// If you have a map of key/value pairs:
Map<String, String> values = new HashMap<String, String>();
for(Entry<String, String> entry : values.entrySet())
doReflection(bean, entry.getKey(), entry.getValue());
}