Develop Reference

Variable in for loop is giving a message that "The value of the local variable i is not used"

I wrote a for loop that is supposed to determine if there is user input. If there is, it sets the 6 elements of int[] valueArr to the input, a vararg int[] statValue. If there is no input, it sets all elements equal to -1.
if (statValue.length == 6) {
for (int i = 0; i < 6; i++) {
valueArr[i] = statValue[i];
}
} else {
for (int i : valueArr) {
i = -1;
}
}
I am using Visual Studio Code, and it is giving me a message in for (int i : valueArr) :
"The value of the local variable i is not used."
That particular for loop syntax is still new to me, so I may be very well blind, but it was working in another file:
for(int i : rollResults) {
sum = sum + i;
}
I feel that I should also mention that the for loop giving me trouble is in a private void method. I'm still fairly new and just recently started using private methods. I noticed the method would give the same message when not used elsewhere, but I do not see why it would appear here.
I tried closing and reopening Visual Studio Code, deleting and retyping the code, and other forms of that. In my short experience, I've had times where I received errors and messages that should not be there and fixed them with what I mentioned, but none of that worked here.

for (int i : valueArr) {
.... CODE HERE ...
}
This sets up a loop which will run CODE HERE a certain number of times. Inside this loop, at the start of every loop, an entirely new variable is created named i, containing one of the values in valueArr. Once the loop ends this variable is destroyed. Notably, i is not directly the value in valueArr - modifying it does nothing - other than affect this one loop if you use i later in within the block. It does not modify the contents of valueArr.
Hence why you get the warning: i = -1 does nothing - you change what i is, and then the loop ends, which means i goes away and your code hasn't changed anything or done anything, which surely you didn't intend. Hence, warning.
It's not entirely clear what you want to do here. If you intend to set all values in valueArr to -1, you want:
for (int i = 0; i < valueArr.length; i++) valueArr[i] = -1;
Or, actually, you can do that more simply:
Arrays.fill(valueArr, -1);
valueArr[i] = -1 changes the value of the i-th value in the valueArr array to -1. for (int i : valueArr) i = -1; does nothing.

While loop doesn't continue even though condition still holds true

I was tasked to create a simulation of a Bank. So far the progress I've made are generating random Client objects, making 4 objects of Teller, putting the Client objects into a circular queue and putting a Client into an empty Teller if there are any.
The problem I have now is that the while loop I made does no continue even though the set condition is still true, it can only execute 5 times. The program still runs though.
This is the code I have so far(assume all variables are declared):
public void run() {
int counter = 1;
populateTellers(windowArray);
while (counter < 10) {
newClient = generateClient();
System.out.println(newClient.toString() + " arrived at :" + counter);
System.out.println();
clientQueue.enqueue(newClient);
clientList.add(newClient);
System.out.println("The Queue now contains " + clientQueue.numberOfOccupiedCells() + " Client(s):");
for (int x = 0; x < clientList.size(); x++) {
System.out.println(clientList.get(x).toString());
}
System.out.println();
arrayIndex = getATeller(windowArray);
if (arrayIndex != -1) {
clientList.remove(0);
clientQueue.dequeue();
windowArray[arrayIndex].setClient(newClient);
windowArray[arrayIndex].setServiceTime(newClient.getDuration());
System.out.println(windowArray[arrayIndex].getName() + " now serves " + newClient.toString());
} else {
for (int x = 0; x < clientList.size(); x++) {
if (windowArrray[arrayIndex].getServiceTime() == counter) {
windowArray[arrayIndex].setClient(new Client());
System.out.println(windowArray[arrayIndex].getName() + " ends service for " + newClient.toString());
}
}
}
counter++;
}
}
The one thing that I can't get head around is that when I remove the code from aI = getATeller(wA); 'till the closing bracket of the if statement below it the program would work. I've tried putting the block into a method, changing the positions of the codes inside if(){} and else{} and changing the condition to if(aI==1), still I got no improvements. Any idea on what I'm doing wrong?
EDIT: So I've been able to narrow it down to a line of code which is windowArray[arrayIndex].setServiceTime(newClient.getDuration());, whenever I assign a value to a Teller's service time the problem would occur, I've checked my Teller class and there was no error there. Any ideas how I can solve this.

Why is it only executing 5 times? According to the code, counter is used as the used to check if it should continue looping for not. The only instance where counter is changed is at last line: counter++.
I can guess that you did a System.out.print on the counter, and it ends up to 5, and it magically stops. Most likely it's throwing an exception, which is not caught, and is lost in the void.
Edit: If this piece of code is being run on another thread, then maybe it's hanging up on some function. Do as told here

Try to find where your loop was turning to infinite loop,
Try writing printing statements, wherever necessary, just to find the flow of execution.
Then printout your variable values, too check whether they were as expected, keep on narrowing your scope as you find error occurred in certain scope, then you will find the culprit, if it is leading you to some other function, then thoroughly check that particular function.

Out of Bounds Exception, need advice

I've read gone through the tutorials, so by all means, if you see something that I've done wrong here, please tell me so I can learn to better-participate on this site.
The getPerishedPassengers method below is giving me an out of bounds exception. I have researched and researched, and I seem to be populating the array properly, and I don't know what is wrong with the method that I've created either. Could someone guide me in the right direction as to how to overcome this exception? Thank you folks!
Here's the main/method:
int passengerMax = 2000;
int passengerActual = 0;
//Create a 2D array that will store the data from the .txt file
String[][] passengerData = new String[passengerMax][6];
//Constructor to read the file and store the data in the array
Titanic(String file) throws FileNotFoundException {
try (Scanner fileIn = new Scanner(new File(file))) {
//Conditional for reading the data
while (fileIn.hasNextLine()) {
//tab through the data to read
passengerData[passengerActual++] = fileIn.nextLine().split("\t");
}
}
}
public int getTotalPassengers() {
return passengerActual;
}
//Method for getting/returning the number of passengers that perished
public int getPerishedPassengers() {
int count = 0;
//For loop w/conditional to determine which passengers perished
for (int i = 0; i < getTotalPassengers(); i++) {
int survive = Integer.parseInt(passengerData[i][1]);
/*The program reads the file and if 1, the passenger survived. If 0,
the passenger perished. Conditional will add to the count if they
survived*/
if (survive == 0) {
count++;
}
}
return count;
}
Here's the stacktrace I'm receiving. I can include the test code as well if you folks would like. Thanks in advance:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at titanic.Titanic.getPerishedPassengers(Titanic.java:66)
at titanic.testTitanic.main(testTitanic.java:68)
Java Result: 1

From what I can see above, the issue is in the line:
int survive = Integer.parseInt(passengerData[i][1]);
My best guess, lacking your input file, is that when you are reading the file, at least one line creates an array of length 0 or 1. In all likelihood, if the last line of the file is an empty line, it would be this line which is causing your array out of bounds exception, as the split would create an array of length 0. Another cause would be a line which lacks any tab in it at all (say a space instead of tabs, etc.) will create a length 1 array, of which passengerData[i][1] will not exist, only passengerData[i][0] will.
Assuming that your input file does not have any lines which are improperly formatted / lack the appropriate number of tabs, I would suggest changing this line in the file read loop:
passengerData[passengerActual++] = fileIn.nextLine().split("\t");
to:
String incomingLine = fileIn.nextLine().trim();
if (null != incomingLine && !incomingLine.isEmpty()) {
passengerData[passengerActual++] = incomingLine.split("\t");
}

Recursive grep with good efficiency

This question is very specific to me, so I cannot find related questions on Stack Overflow. So, I'm coding a grep shown below. I am confused on the stringindextoutofboundexception. The reason for that is because I am checking whether it is equals to \0. That means I am handling the out of bound exception, no?
Example:
grep("hello","llo");
This will return 3. That is because its start matching at original[2] which is position 3. However, I am encountering an out of index error. I've spent hours and I can't figure it out.
public static int grep(String ori, String ma){
int toReturn = 0;
int oCounter = 0;
int i = 0;
while (i < ma.length()){
if (ori.charAt(toReturn) == ma.charAt(i)){
i++;
if (ma.charAt(i) == '\0'){ // error on this line
return toReturn;
}
toReturn++;
if (ori.charAt(toReturn) == '\0'){ // and this line if i delete the section above.
return -1;
}
} else {
i = 0;
toReturn++;
}
}
return -1;
}

You're getting an StringIndexOutOfBoundsException because you increment i inside the loop at a too early and wrong stage.
Checking for \0 is a C++ thing. Strings in java are not \0 terminated.
What you're writing is already done in the String class. There are several methods available.
System.out.println("hello".indexOf("llo"));
will print 2 because it's been found and starts at index 2. Feel free to add 1 if you dislike the starting at 0 for some reason.
You also ask "that means I'm handling the exception, no?". No, it doesn't. Exceptions are handled with a special syntax called try-catch statements. And example:
try {
// possibly more lines of code here
do_something_that_might_cause_exception();
// possibly more lines of code here
} catch (Exception e) {
// something did indeed cause an exception, and the variable e holds information about. We can do "exceptional" handling here, but for now we print some information.
e.printStackTrace();
}

Changing recursive method to iterative

i have recrusive function which works fine. The problem is it gives stackoverflow error when the number of lines are huge. I want to put it in iterative, probably using a for loop. Need some help in doing it.
private TreeSet validate(int curLine, TreeSet errorSet) {
int increment = 0;
int nextLine = 0;
if (curLine == lines.length || errorSet.size() != 0) {
return errorSet;
} else {
String line = lines[curLine];
//validation starts. After validation, line is incremented as per the requirements
increment = 1 //As per requirement. Depends on validation results of the line
if (increment > 0) {
try{
Thread.currentThread().sleep(100);
}catch(Exception ex){
System.out.println(ex);
}
nextLine = (curLine + increment);
validate(nextLine, errorSet);
}
}
return errorSet;
}
Poster's description of the method:
The method does validates textlines, these lines has instructions of how much line has to be skipped, if the line is valid. So, if the line is valid that many of lines will be skipped using the increment. if the line is not valid increment will be 0.

I'm not sure why this was ever recursive in the first place. This is perfectly suited for the use of a FOR loop. use something like so:
private TreeSet validate(int curLine, TreeSet errorSet) {
int increment = 0;
if (errorSet.size() != 0)
return errorSet;
for (int curLine = 0; curLine < lines.Length; curLine += increment)
{
// put your processing logic in here
// set the proper increment here.
}
}
If the increment is always going to be 1, then you can just use curr++ instead of curLine += increment

for(String line : lines) {
// validate line here
if(!errorSet.isEmpty()) {
break;
}
}

The solution for your problem could be simple for loop or while, with logical expression for stop condition. Typically we use for loop when we have to pass through all elements of Iterable or array. In case when we are not aware how many loops we are going to do we use a while loop. Advantage of for loop over while, is that we for free have localized variables so we ca not use them out side of the loop, therefore we reduce possibility to have some bug.
You problem is that you have to break the program on two conditions:
When errorSet is not empty.
When the array of lines have no longer items.
As contradiction, we can say that your program should continue:
Until errorSet is empty,
and until line number is smaller than array size where they are stored.
This provide us to simply expression
errorSet.isEmpty()
lineNumber < lines.length()
We can combine them using logical operator && and use as a stop rule in for loop.
for(int lineNumber= 0; errorSet.isEmpty() && lineNumber< lines.length(); lineNumber++) {
//code to operate
}
Note:
Typically for logical expression is used operator &&, that assure that every part of the logical expression is evaluated. An alternative for this is &, that in case of false do not operate longer and return false. We could be tempted to use this operator for this expression but i would be bad idea. Because when we would traversed all lines without error code will generate IndexOutOfBoundException, if we switch the places then we would not have any optimization as first expression would be evaluated same number of times.