Develop Reference

MongoDB returning field as null

I am currently working on an application connected to a MongoDB instance. I am having trouble where the 'id' field of my object is not being returned to me within the application but is being returned as null.
The schema has an 'entity' as defined below:
{
"entity_id": String,
"parent": String,
"relevance": boolean
}
I'm querying the collection using the Java Sync Driver (4.4.1) like so:
try {
Entity testDoc = collection.find(eq("entity_id", entity_id)).first();
if (testDoc != null) {
//add entity to a list
}
} catch (Exception e) {
LOGGER.log(Level.SEVERE, "Failed to get Entity", e);
}
For some reason this will give me every field in the object when I query EXCEPT the entity_id. I keep getting this returned as:
entity_id= null
Two things stick out to me. The first being that every other field is a String (originally the Id was a UUID object but I simplified while troubleshooting) and they still return if it's other fields. The second being that there is a whitespace before this null value as if it's being formatted. Other null values return as field=null instead of field= null
I was looking to see if there is some security setting preventing things from being labeled as *_id or *id from being returned but I have found no such instance.
Edit: Here is the Entity Pojo for clarity
public class Entity {
#BsonProperty(value = "entity_id")
private String entityID;
#BsonProperty(value = "parent")
private String parent;
#Deprecated
#BsonProperty(value = "relevance")
private boolean relevance;
public Entity() {}
public Entity(String entityID, String parent, Boolean relevance) {
this.entityID = entityID;
this.parent = parent;
this.relevance = relevance;
}
public String getEntityID() {
return entityID;
}
public void setEntityID(String entityID) {
this.entityID = entityID;
}
public String getParent() {
return parent;
}
public void setParent(String parent) {
this.parent = parent;
}
public boolean isRelevant() {
return relevance;
}
public void relevance(boolean relevance) {
this.relevance = relevance;
}
}

So update for anyone watching this, it appears to have been an issue with my Eclipse IDE.
I reimported the project into IntelliJ Community Edition and rebuilt the Maven project, etc... After doing so, the test cases passed and my entityID returns in the query. Hopefully if anyone else runs into this issue they can do something similar.

values of a object stored in a linked list printing but not useable

I am fairly new to java and working on a project to simulate a CPU scheduler in Java and i am using a linked list to store each process object that is read in from a external master list. When I test print the processes and the variables they contain, everything comes out as expected but whenever I try and do something with them it stops working.
public class process
String ID;
int Arrive;
int ExecSize;
int Execstore;
int Tstart;
int Tend;
int quant;
public process(String ID,int Arrive,int ExecSize) {
this.ID = ID;
this.Arrive = Arrive;
this.ExecSize = ExecSize;
this.Execstore=ExecSize;
this.Tend = 0;
this.Tstart = 0;
this.quant = 4;
}
public void setquant(int update) {
this.quant = update;
}
public int getquant() {
return quant;
}
public void setExecSize(int update) {
this.ExecSize = update;
}
public void setTend(int update) {
this.Tend = update;
}
public void setTstart(int update) {
this.Tstart = update;
}
String getID() {
return ID;
}
int getArrive() {
return Arrive;
}
int getExecSize() {
return ExecSize;
}
int getTstart() {
return Tstart;
}
int getTend() {
return Tend;
}
int getExecstore() {
return Execstore;
}
and this is the class used for the simulation
public class fcfs {
int disp;
int Ttotal = 0;
int Exec;
int Turn;
int Wait;
String output;
LinkedList<process> Que = new LinkedList<process>();
LinkedList<process> Quecleared = new LinkedList<process>();
public fcfs(LinkedList<process> B,int D) {
Que.addAll(B);
disp=D;
}
public void run()
{
while (Que != null)
{
Ttotal = Ttotal + disp;
System.out.println(Que.getFirst().getExecSize());
Exec=Que.getFirst().getExecSize();
output += String.format("T%d: %s\n",Ttotal,Que.getFirst().getID());
Que.getFirst().setTstart(Ttotal);
Ttotal = Ttotal+Exec;
Que.getFirst().setTend(Ttotal);
Quecleared.add(Que.poll());
}
}
So whenever i use System.out.println I get the expected result that I read into the list. But anything else I try to do in reference to elements of the process object will not work. Any help would be greatly appreciated

while (!Que.isEmpty())
{
Ttotal = Ttotal + disp;
System.out.println(Que.peekFirst().getExecSize());
Exec=Que.peekFirst().getExecSize();
output += String.format("T%d: %s\n",Ttotal,Que.peekFirst().getID());
Que.peekFirst().setTstart(Ttotal);
Ttotal = Ttotal+Exec;
Que.peekFirst().setTend(Ttotal);
Quecleared.add(Que.pollFirst());
}
This shouldn't throw an error on Exec = Que.peekFirst().getExecSize();
That error is thrown when your container is empty.
EDIT
In your code you specified the condition Que != null. In java once an object has been instantiated it is no longer considered null even if it IS empty. Most likely what was happening here is you continued iterating through your while(Que != null) loop until you had called Que.poll() on all elements of the list.
After clearing the list you did not exit the loop because Que still was not null. Then calling getFirst() on the empty instance of a LinkedList threw an exception.
A similar situation can be seen here with null vs empty strings:
Difference between null and empty ("") Java String
EDIT 2
It also appears that your class methods for getID(), getExecSize(), etc are passing values by reference as opposed to copying their value. Thus any change you make after passing the reference from queue will alter any copies you tried to make of it.
This can be best avoided by creating a new instance of an object and returning that from your function. Shown in an answer on the question linked below:
class Foo {
private Bar myBar;
public Foo deepCopy() {
Foo newFoo = new Foo();
newFoo.myBar = myBar.clone(); //or new Bar(myBar) or myBar.deepCopy or ...
return newFoo;
}
}
For more information on ways to pass values as opposed to reference values of your pre-existing instances, as well as what a shallow copy actually is, check this link: In Java, what is a shallow copy?

Randomly Generate a Tree Structure Consisting of Objects with their Parents

I'm trying to randomly generate a tree structure of objects that look something like the following:
Branch parent = new Branch("Start");
Branch branch1 = new Branch(parent, "Branch 1");
Branch branch2 = new Branch(parent, "Branch 2");
Branch branch21 = new Branch(branch2, "Branch 2.1");
Branch branch22 = new Branch(branch2, "Branch 2.2");
I know how to create objects manually, and how to generate random numbers, and I've seen some stuff on randomly generating nodes for creating fractals, but I'm pretty lost all the sudden, as I've never had to programmatically generate objects before.
Any ideas as to where to start, or what technique to use would be appreciated.

Typically, when building such items it's good to have a designed in and out. Otherwise, you will find yourself having to support many methods of application to support the intended result.
Hope this helps!
Try something along the following :)
Branch start = new Branch();
CreateChildren(start);
const int ChildrenLimitCheck = 0;
private void CreateChildren(Branch parent) {
//Use a limit variable so that you can decrease, and if it's equal to a sepcific number(usually 0) exit.
int Limit = (int) (Math.random() * 5);
//Call the function that's recursive, inside of a function that isn't recursive. This gives you a clean way to interface with the recursive function without excessive lines of code in other areas
generateChildren(parent,Limit);
}
private void generateChildren(Branch parent,int limit) {
//Check to see if we've hit our minimum. If so, exit out of the logic
if(limit == ChildrenLimitCheck)
return;
//Specify the random number of branches created in this instance
int numberOfBranches = (int) (Math.random() * 5);
for (int i = 0; i < numberOfBranches; i++) {
Branch child = new Branch(parent);
parent.Children.Add(child);
//Depending on what you want to do, either pass i or pass limit. If you don't use limit, you can remove it from this function :)
//If you pass i, try doing:
//for (int i = numberOfBranches; i > 0; i--)
//So that you can eventually get down to 0, to automatically stop your recursive calls with the above return statement.
//Seems you just want to run a loop for xxx number of times. This will still grant that, but you won't have to guess the upper limit
//of numberOfBranches to exit on, and you'll be able to exit cleanly
//This may be what caused your stackoverflow error. For all recursive functions, you need an exit condition or it will run indefinately
generateChildren(child,--limit);
//generateChildren(child,i);
}
}

I do this quite often and I can definately help in some areas of efficiency.
Try logic similar to the following. Place a breakpoint at Console.Write to see depth. This is a C++ object oriented approach, which I personally prefer over LINQ for performance. I didn't fine tune this, so LINQ may be faster. But if you know what you're doing, you can significantly increase performance via custom methods and inheritance.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication11
{
public class Branch
{
//Branch Name
public string BranchName { get; set; }
//Add depth
public List<Branch> Children = new List<Branch>();
//Add a parent
public Branch Parent = null;
public Branch()
{
}
public Branch(string BranchName)
{
this.BranchName = BranchName;
}
public Branch(Branch Parent, string BranchName)
{
this.Parent = Parent;
this.BranchName = BranchName;
}
//Internal Functions
public bool HasParent()
{
return this.Parent != null;
}
public Branch getParent()
{
return this.Parent;
}
}
//Wrap a list inside of a class so we can have leverage over the add, and create our own functions for our need
public class BranchList
{
public List<Branch> branchParentList = new List<Branch>();
public void AddBranchToParent(Branch parent, Branch child)
{
foreach (Branch node in branchParentList)
{
if (node == parent)
{
node.Children.Add(child);
}
}
}
public void AddBranchAsChild(string parent, Branch child)
{
foreach (Branch node in branchParentList)
{
if (node.BranchName == parent)
{
node.Children.Add(child);
return;//Exit out, don't do the other loop. We found it
}
//Depth
AddBranchAsChildInChildren(node, child,parent);
}
}
public void AddBranchAsChildInChildren(Branch branch,Branch Child,string parent)
{
foreach(Branch child in branch.Children)
{
if (child.BranchName == parent)
child.Children.Add(Child);
}
}
public void AddBranchAsChildInChildren(Branch branch, string Child, string parent)
{
foreach (Branch child in branch.Children)
{
if (child.BranchName == parent)
child.Children.Add(new Branch() { BranchName=Child });
}
}
public void AddBranchAsChild(string parent, string child)
{
foreach (Branch node in branchParentList)
{
if (node.BranchName == parent)
{
node.Children.Add(new Branch() { BranchName = child });
return;
}
//Depth
AddBranchAsChildInChildren(node, child, parent);
}
}
public void AddBranchAsParent(Branch Branch, Branch Child)
{
if (branchParentList.Contains(Branch) == false)
throw new Exception("Parent exists");
foreach (Branch b in branchParentList)
{
if (b == Child)
{
b.Parent = Branch;
}
}
}
public void AddParent(Branch Parent)
{
if (branchParentList.Contains(Parent))
throw new Exception("Parent exists");
this.branchParentList.Add(Parent);
}
}
//Wrap the list, use it as an interface
public class BranchManager
{
public BranchList branchList = new BranchList();
public BranchManager()
{
}
public void AddParent(Branch Branch)
{
branchList.AddParent(Branch);
}
public void AddBranchAsChild(Branch Parent, Branch Child)
{
branchList.AddBranchToParent(Parent, Child);
}
public void AddBranchAsChild(string ParentName, Branch Child)
{
branchList.AddBranchAsChild(ParentName, Child);
}
public void AddBranchAsChild(string ParentName, string ChildName)
{
branchList.AddBranchAsChild(ParentName, ChildName);
}
}
class Program
{
static void Main(string[] args)
{
/*
Branch parent = new Branch("Start");
Branch branch1 = new Branch(parent, "Branch 1");
Branch branch2 = new Branch(parent, "Branch 2");
Branch branch21 = new Branch(branch2, "Branch 2.1");
Branch branch22 = new Branch(branch2, "Branch 2.2");
*/
BranchManager branchManager = new BranchManager();
branchManager.AddParent(new Branch("Start"));
branchManager.AddBranchAsChild("Start", "Branch 1");
branchManager.AddBranchAsChild("Start", "Branch 2");
branchManager.AddBranchAsChild("Branch 2", "Branch 2.1");
branchManager.AddBranchAsChild("Branch 2", "Branch 2.2");
Console.WriteLine(branchManager.branchList.branchParentList.Count);
}
}
}

Best guess so far, using a recursive function to handle the randomly generating children & parents:
Branch start = new Branch();
generateChildren(start);
private void generateChildren(Branch parent) {
int numberOfBranches = (int) (Math.random() * 5);
for (int i = 0; i < numberOfBranches; i++) {
Branch child = new Branch(parent);
generateChildren(child);
}
}
It properly creates a list of Branch objects with linked parents. I ran into a StackOverflow error until I wrapped it in a counter that limits the total number of branches.
The real question is: Is there a non-recursive way to handle it?

Updating the value of arraylist

I have a static data inside my arraylist in a controller package. These are my codes in the controller package.
for(int i=0;i<studentPic.length;i++){
//i want to update the value of zero
mStudentModels.add(new StudentModel(studentPic[i],status[i],studentName[i],courseAndYear[i],0));
}
public List<StudentModel> getStudentModels (){
return mStudentModels;
}
Now i want to update a certain data if it meets a certain condition:
private void stopCountdown() {
if (mTask != null) {
mTask.interrupt();
List<StudentModel> studentModels = studentData.getStudentModels();
studentData = new StudentData();
for(int i=0;i<studentModels.size();i++){
StudentModel studentModel = studentModels.get(i);
if(studentModels.get(i).getStatus()=="PRESENT"){
mFirebaseDatabase.child("attendance").child(formattedDate).child("present").push().setValue(studentModel);
}else if(studentModels.get(i).getStatus()=="LATE"){
mFirebaseDatabase.child("attendance").child(formattedDate).child("late").push().setValue(studentModel);
}else{
//i want to update the value of zero here
int absences = studentModel.getNumOfAbsences();
studentModel.setNumOfAbsences(absences+1);
mFirebaseDatabase.child("attendance").child(formattedDate).child("absent").push().setValue(studentModel);
}
}
}
}
The problem is if i call studentData.getStudentModels(); the value always remains zero. Whats the problem with that?
Here's my controller:
public class StudentData {
private List<StudentModel> mStudentModels;
public void setmStudentModels(List<StudentModel> mStudentModels) {
this.mStudentModels = mStudentModels;
}
public StudentData(){
mStudentModels = new ArrayList<>();
int[] studentPic = {R.drawable.boy1, R.drawable.boy2, R.drawable.girl1, R.drawable.girl2, R.drawable.girl3,
R.drawable.girl4, R.drawable.girl5, R.drawable.boy3, R.drawable.girl6, R.drawable.girl7,
R.drawable.boy4, R.drawable.girl8, R.drawable.girl9, R.drawable.girl10, R.drawable.boy5,
R.drawable.girl1, R.drawable.girl12, R.drawable.girl13, R.drawable.boy6, R.drawable.girl14};
String[] status = {"ABSENT","LATE","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT","PRESENT",
"PRESENT","PRESENT","PRESENT","ABSENT","PRESENT","PRESENT","PRESENT","PRESENT"};
String[] studentName = {"Andy Lim", "Benjamin Adams", "Karen Healey", "Anne Pierre", "Corine Alvarez",
"Emily Hedrick", "Courtney Quick", "Oscar Renteria", "Ellen Joy", "Jesse Ramer",
"Jackson Beck", "Alicia Hofer", "Jenae Rupp", "Allison Beitler", "Martin Hofkamp",
"Emma Ruth", "Kathryn Berg", "Michelle Salgado", "Lewis Caskey", "Elizabeth Core"};
String[] courseAndYear = {"BSIT-3", "BSIT 2", "BSIT-3","BSCS-3" , "BSCS-2", "BSIT-3", "BSIT-2", "BSIT-3", "BSIT-2", "BSIT-3",
"BSCS-3", "BSCS-2", "BSCS-3", "BSCS-2", "BSCS-3", "BSIT-3", "BSCS-2", "BSIT-2", "BSCS-3", "BSCS-2"};
for(int i=0;i<studentPic.length;i++){
mStudentModels.add(new StudentModel(studentPic[i],status[i],studentName[i],courseAndYear[i],0));
}
}
public List<StudentModel> getStudentModels (){
return mStudentModels;
}
}
My model looks like this:
public StudentModel(int studentPic, String status, String studentName, String courseAndYear, int numOfAbsences) {
this.studentPic = studentPic;
this.status = status;
this.studentName = studentName;
this.courseAndYear = courseAndYear;
this.numOfAbsences = numOfAbsences;
}

Looks like below checks need to do:
Whether studentPic is not empty.
Whether mStudentModels is not empty (Mainly whether mStudentModels is getting added before the call of stopCountdown() method).
If it does not fix the issue, please provide more information on the code of Controller side.

Get children with Lucene's TaxonomyReader

In Lucene, I am using the TaxonomyReader to read an index of a taxonomy stored in my disk. For a given category, I need to find all categories that are its children. However, in the Lucene's API I could find a method to retrieve the parent but not with the children. There is a method called getChildrenArrays() that returns a ChildrenArrays object. As you can see, this class only has two methods:
getYoungestChildArray
getOlderSiblingArray
I want to implement Enumerator using these two methods. Does someone know how to do it?

I got the following:
private class EnumChildren implements Enumeration<Integer> {
int category, current;
int[] next, first;
public EnumChildren(int category) {
ChildrenArrays childrenArrays = tr.getChildrenArrays();
first = childrenArrays.getYoungestChildArray();
next = childrenArrays.getOlderSiblingArray();
current = first[category];
}
public boolean hasChildren() {
return (current != TaxonomyReader.INVALID_ORDINAL);
}
#Override
public boolean hasMoreElements() {
current = next[current];
return (current != TaxonomyReader.INVALID_ORDINAL);
}
#Override
public Integer nextElement() {
return current;
}
}
Ans is used as:
ordinal = tr.getOrdinal(new CategoryPath(nodeCategory.getPath(), '/'));
EnumChildren childrenEnumeration = new EnumChildren(ordinal);
if (childrenEnumeration.hasChildren()) {
do {
int current = childrenEnumeration.nextElement();
Category child = new Category(tr.getPath(current).toString());
addChildren(child);
nodeCategory.children.add(child);
} while (childrenEnumeration.hasMoreElements());
}