Develop Reference

I'm trying to give the value of an array of a class to another array with the same class, is there something I'm missing here?

The class is called Exposicion and has a String and an INT value, so I used it as an array to grab some input from the user.
class Exposicion {
public String nombreExpo;
public int duracionExpo;
Exposicion(String nombreExpo, int duracionExpo) {
this.nombreExpo = nombreExpo;
this.duracionExpo = duracionExpo;
}
}
With the Function SortExpo I plan to copy only the values of the array as long as the INT values don't add up to 180, but java flags an error when doing:
arrExpoT[posHor].nombreExpo = arrExpoS[k].nombreExpo;
This is the whole function
void SortExpo(Exposicion[] arrExpoS,int posicion,Exposicion[] arrExpoT){
int poshor=0;
int total=0;
for (int k = 0; k < posicion; k++) {
if ( total < 180 || arrExpoS[poshor].nombreExpo != "TOMADO123") {
arrExpoT[poshor].nombreExpo = arrExpoS[k].nombreExpo;
arrExpoT[poshor].duracionExpo = arrExpoS[k].duracionExpo;
arrExpoS[poshor].nombreExpo = "TOMADO123";
total = total + arrExpoS[k].duracionExpo;
poshor++;
} else {
k = posicion;
}
}
}
Error
I've added the .java file in this link
Also Main.java if this helps

You are getting a NullPointerException because "expo1" and "sala1" variables are both null. You have to pass a reference to an object on both variables. Something like this:
class SalaExpo(){
Exposicion[] expo1=new Exposicion[100];
}
public class ConsoleMenu {
private SalaExpo sala1;
void execute(){
sala1 = new SalaExpo();
}
}
Also you should poblate the sala1.expo1 array, like this (don't know if this is what you are intending but you should do this in order not to get a NullPointerException) :
void GuardarExpo(Exposicion[] arrExpoG,int posicion,Exposicion[] arrSala) {
/*
Bunch
of
code
*/
arrExpoG[posicion] = new Exposicion(inputNombre,inputDuracion);
arrSala[posicion]=arrExpoG[posicion];
}
Finally, you should use the variable "posicion" instead of "sala1.expo1.length" to pass as argument to the "imprimirExpo" method, since the array "sala1.expo1" has a length of 100, that means a lot of null elements since you are not poblating it all:
ImprimirExpo(sala1.expo1,posicion);
instead of:
ImprimirExpo(sala1.expo1,sala1.expo1.length);

Dynamic ArrayList fields

I have an assingment for school and I am having trouble with some ArrayLists. I have an input file which has one entry at every line. This entry has an integer and up to four strings. This input file is about locations that a film is filmed. The integer is the movieID in my case and the strings are the locations. However not every film has 4 locations which means that when my program tries to load the file it returns an error because it expects 5 fields at every row and this never happens because I have movies with 1 or 2 or the locations. I use a data loader class because I have to load several different files. My other files have a specific number of entries and fields at each row so loading those isn't a problem. The load process is done by adding the file into an array list and then creating the objects needed. I know that I need the program somehow to understand the empty fields and maybe handle them dynamically, for example a movie has 3 locations so the 4th field is empty, but I haven't figured it out yet. Any suggestions? Thank you!
This is my LocationsLoader class.
package dataLoader;
import java.util.ArrayList;
import dataModel.Locations;
public class LocationsLoader extends AbstractFileLoader<Locations>{
public int constructObjectFromRow(String[] tokens, ArrayList<Locations> locations) {
int movieID;
List<String> loc = new List();
movieID = Integer.parseInt(tokens[0]);
loc = tokens[]; // What goes here?
Locations l;
l = new Locations(movieID, loc);
locations.add(l);
System.out.println(l);
//System.out.println(locations.toString());
return 0;
}
}
And this is my Locations class:
package dataModel;
public class Locations {
private int movieID;
private List<String> loc;
public Locations(int otherMovieID, List<String> otherLocations) {
this.movieID = otherMovieID;
this.loc = otherLocations;
}
public int getMovieID() {
return movieID;
}
public void setMovieID(int id) {
this.movieID = id;
}
public String getLocations(int index) {
return loc.get(index);
}
}
}

You fill an array here
String[] tokens = new String[numFields];
for (int i = 0; i < numFields; i++) {
tokens[i] = tokenizer.nextToken();
}
but arrays are fixed length, there's really no reason to use them if you can have fewer values. Fill a list instead.
List<String> tokens = new ArrayList<>();
while (tokenizer.hasNextToken()) {
String token = tokenizer.nextToken().trim();
if (!token.isEmpty()) {
tokens.add(tokenizer.nextToken());
}
}
In fact, I'm not sure why you would need to give the reader the number of expected tokens at all.
But as Dodgy pointed out, you might as well use String#split:
String[] tokens = line.split(delimiter);
which will yield empty Strings as well, but you can just ignore those in your constructObjectFromRow function.

Java Object Without a Class

I don't know if this is possible in Java but I was wondering if it is possible to use an object in Java to return multiple values without using a class.
Normally when I want to do this in Java I would use the following
public class myScript {
public static void main(String[] args) {
// initialize object class
cl_Object lo_Object = new cl_Object(0, null);
// populate object with data
lo_Object = lo_Object.create(1, "test01");
System.out.println(lo_Object.cl_idno + " - " + lo_Object.cl_desc);
//
// code to utilize data here
//
// populate object with different data
lo_Object = lo_Object.create(2, "test02");
System.out.println(lo_Object.cl_idno + " - " + lo_Object.cl_desc);
//
// code to utilize data here
//
}
}
// the way I would like to use (even though it's terrible)
class cl_Object {
int cl_idno = 0;
String cl_desc = null;
String cl_var01 = null;
String cl_var02 = null;
public cl_Object(int lv_idno, String lv_desc) {
cl_idno = lv_idno;
cl_desc = lv_desc;
cl_var01 = "var 01";
cl_var02 = "var 02";
}
public cl_Object create(int lv_idno, String lv_desc) {
cl_Object lo_Object = new cl_Object(lv_idno, lv_desc);
return lo_Object;
}
}
// the way I don't really like using because they get terribly long
class Example {
int idno = 0;
String desc = null;
String var01 = null;
String var02 = null;
public void set(int idno, String desc) {
this.idno = idno;
this.desc = desc;
var01 = "var 01";
var02 = "var 02";
}
public int idno() {
return idno;
}
public String desc() {
return desc;
}
public String var01() {
return var01;
}
public String var02() {
return var02;
}
}
Which seems like a lot of work considering in Javascript (I know they are different) I can achieve the same effect just doing
var lo_Object = f_Object();
console.log(lo_Object["idno"] + " - " + lo_Object[desc]);
function f_Object() {
var lo_Object = {};
lo_Object = {};
lo_Object["idno"] = 1;
lo_Object["desc"] = "test01";
return lo_Object;
}
NOTE
I know the naming convention is wrong but it is intentional because I have an informix-4gl program that runs with this program so the coding standards are from the company I work for

The best way to do this is to use HashMap<String, Object>
import java.util.HashMap;
public class Main {
public static void main(String[] args) {
HashMap<String, Object> person =
new HashMap<String, Object>();
// add elements dynamically
person.put("name", "Lem");
person.put("age", 46);
person.put("gender", 'M');
// prints the name value
System.out.println(person.get("name"));
// asures that age element is of integer type before
// printing
System.out.println((int)person.get("age"));
// prints the gender value
System.out.println(person.get("gender"));
// prints the person object {gender=M, name=Lem, age=46}
System.out.println(person);
}
}
The advantage of doing this is that you can add elements as you go.
The downside of this is that you will lose type safety like in the case of the age. Making sure that age is always an integer has a cost. So to avoid this cost just use a class.

No, there is no such a feature, you have to type out the full type name(class name).
Or use may use val :
https://projectlombok.org/features/val.html
Also, if you use IntelliJ IDEA
try this plugin :
https://bitbucket.org/balpha/varsity/wiki/Home

I am not sure if it's possible with Java. Class is the primitive structure to generate Object. We need a Class to generate object. So, for the above code, i don't think there is a solution.

Java methods only allow one return value. If you want to return multiple objects/values consider returning one of the collections. Map, List, Queue, etc.
The one you choose will depend on your needs. For example, if you want to store your values as key-value pairs use a Map. If you just want to store values sequentially, use a list.
An example with a list:
list<Object> myList = new ArrayList<Object>();
myList.add("Some value");
return myList;
As a side note, your method create is redundant. You should use getters and setters to populate the object, or populate it through the constructor.
cl_Object lo_Object = new cl_Object(1, "test01");
The way you have it set up right now, you're creating one object to create another of the same type that has the values you want.
Your naming convention is also wrong. Please refer to Java standard naming convention:
http://www.oracle.com/technetwork/java/javase/documentation/codeconventions-135099.html#367

Java Adding multiple elements to an ArrayList

Still new to java, but I'm having an issue adding multiple new elements to my arraylist.
The idea for this method is to look and see if a name is already in the list, and if so return false, and if not then add the name and person's score to the arraylist.
I keep getting an error when I try to add it in. The add will work if it's just the name portion I add in, but once I also include the scoreOn1st it gives me an error.
public boolean addGolfer(String name, int scoreOn1st)
{
// check if the golfer is already in the collection
for (int i = 0; i < board.size(); i++)
{
if (board.get(i).equals(name))
{
return false;
}
}
// otherwise
board.add(new ScoreCard(name, scoreOn1st));
return true;
}
This is the constructor class already created for the arraylist:
public ScoreBoard(String tourneyName)
{
// initialize instance varable
this.tournament = tourneyName;
ArrayList<ScoreCard> board = new ArrayList<ScoreCard>();
}

The board should be declared outside. You can new it inside the constructor. The get !method returns a ScoreCard object on which you cannot directly call equals name.
public class ScoreBoard {
List<ScoreCard> board;
public ScoreBoard(String tourneyName)
{
this.tournament = tourneyName;
this.board = new ArrayList<ScoreCard>();
}
ScoreCard should be something like this:
class ScoreCard {
ScoreCard(String name) {//definition } //1st Constructor
ScoreCard(String name, int score) { //definition } //2nd Constructor

In the constructor the board variable is a method variable not a field.
public ScoreBoard(String tourneyName)
{
// initialize instance varable
this.tournament = tourneyName;
this.board = new ArrayList<ScoreCard>(); // I assume you have declared this field.
}

NullPointerException while indexing variable String parameters

I'm new to the idea of using an ellipsis. I'm almost certain my error is caused by improperly declaring or initializing "String[] authors", but I don't know how to do this an still have my setAuthors method work.
import java.util.*;
public class Book {
private String[] authors; //I'm guessing this line should end with "= new String..."
//but not sure how to w/o specifying an array dimension
private int authorsSize;
//Receives variable # of String parameters and indices them into String[] "authors"
public void setAuthors(String... authors) {
authorsSize = authors.length;
for(int i=0;i<authorsSize;i++)
this.authors[i] = authors[i];
}
//getAuthors method:
public String getAuthors(){
String s = "";
authorsSize = authors.length;
for(int i=0;i<authorsSize;i++)
s = s+authors[i] + ", ";
printAuthors = s;
return s;
}

The simplest approach would just be to clone the array:
public void setAuthors(String... authors){
this.authors = (String[]) authors.clone();
}
After all, you're overwriting the previous data anyway, and you can't know the size before the method call. You don't need the authorsSize variable at this point - you've got the authors array which knows its own length.
(If you were able to use immutable collections, you wouldn't even need to bother cloning, of course.)
EDIT: As noted in comments, this method will throw an exception if you pass in a null reference. You shouldn't automatically decide that this is a situation you should "handle" - it's entirely legitimate to document that the parameter must not be null. I would suggest documenting the behaviour around nullity either way.
Indeed, if you do this you might also want to initialize your instance field like this:
private String[] authors = new String[0];
That way you always know you'll have a non-null reference in that field, so you can use it with impunity. I would prefer this over having to check for null on every use.

you never initialized authors your array .
you need to initialize it before you use it .
String[] authors = new String[size];
//but not sure how to w/o specifying an array dimension
The best way is to use an List implementing classes as they are dynamic Arrays. i.e., you dont need to specify the size.
List<String> authors = new ArrayList<String>();

You have to currect your setAuthors method as described below
public void setAuthors(String... authors) {
if (authors != null && authors.length > 0) {
authorsSize = authors.length;
authors = new String[authorsSize];
for (int i = 0; i < authorsSize; i++)
this.authors[i] = authors[i];
}else{
this.authors = null;
}
}

Because the declaration of "private String[] authors" is before that of "public void setAuthors(String... authors)", you can not use the format like "String[] authors = new String[authorsSize]". This will make the size of authors always be 0.
The better way is to use the dynamic initialization:
List authors = new ArrayList();
Then use this.authors.add(authors[i]) to pass parameters.

you could also adjust your code like so:
import java.util.*;
public class Book{
private String[] authors;
private int authorsSize;
public void setAuthors(String... authors){
//check for null, you could also set this.authors = new String[] if you prefer.
if(authors == null){
this.authors = null;
}else{
authorsSize = authors.length;
//also add this line...
this.authors = new String[authorsSize];
for(int i=0;i<authorsSize;i++)
this.authors[i] = authors[i];
}
}
public String getAuthors(){
if(authors == null){
return ""; //could also return null here if you would prefer
}
StringBuilder s = new StringBuilder();
authorsSize = authors.length;
for(int i=0;i<authorsSize;i++){
if(i > 0)
s.append(",");
s.append(authors[i]);
}
//printAuthors = s;
return s.toString();
}
}