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.

Processing multidimensional array

Hey I can't get processing to run my code due to a NullPointerException on my array value in the println statement.
for (bx=0; bx<=7; bx++) {
for (by=0; by<=4; by++) {
rect(bx*BRICK_WIDTH, by*BRICK_HEIGHT, BRICK_WIDTH, BRICK_HEIGHT);
int[][] a = {{bx}, {by}};
}
println (a[bx][by]);
}

From just the code you posted, I wouldn't expect you to get a NullPointerException. I would expect you to get a The variable "a" does not exist error.
So I'm guessing that you have another a variable at the top of your sketch, like this:
int[][] a;
void draw(){
for (bx=0; bx<=7; bx++) {
for (by=0; by<=4; by++) {
rect(bx*BRICK_WIDTH, by*BRICK_HEIGHT, BRICK_WIDTH, BRICK_HEIGHT);
int[][] a = {{bx}, {by}};
}
println (a[bx][by]);
}
}
Please note that this is why it's so important for you to post a MCVE, so we don't have to guess at what your code is doing.
If this is the case, your problem is caused because the int[][] a = {{bx}, {by}}; line inside the for loop is declaring a different variable with the same name. It's not touching the skethc-level a variable. So the sketch-level a variable still has the default value of null, hence the NullPointerException when you try to use it.
Also note that it doesn't make a ton of sense to assign a to anything inside the for loop. To see why, consider this simpler example:
int x = 0;
for(int i = 0; i < 10; i++){
x = i;
}
println(x);
You'll see that the x variable only "keeps" the last value we assigned to it. The same thing is true of arrays. Maybe you meant to set a particular index of your array?
If you're still having trouble then please post a MCVE. Good luck.

InvocationTargetException while trying to add variables to a new object

I am trying to send two variables from one sketch to another, using the oscP5 library for processing.
The message I am sending is created like this:
OscMessage myMessage = new OscMessage("/test");
myMessage.add(title);
myMessage.add("Zeit");
oscP5.send(myMessage, remoteLocation);
In the second sketch, I receive the data like that:
void oscEvent(OscMessage theOscMessage) {
if(theOscMessage.checkAddrPattern("/test")) {
String title = theOscMessage.get(0).stringValue();
String layoutType = theOscMessage.get(1).stringValue();
addToQueue(title, layoutType);
}
}
And here my simplified addToQueue function:
void addToQueue(String title, String layoutType) {
if(!existsInQueues(title)) {
upcomingHeadlines.add(new Headline(title, printAxis, scrollSpeed, layoutType));
}
}
Every time I start the sketches, I get the error:
ERROR # OscP5 ERROR. an error occured while forwarding an OscMessage to a method in your program. please check your code for any possible errors that might occur in the method where incoming OscMessages are parsed e.g. check for casting errors, possible nullpointers, array overflows ... .
method in charge : oscEvent java.lang.reflect.InvocationTargetException
I have been able to track the problem down to the layoutType-Variable. If I change
String layoutType = theOscMessage.get(1).stringValue();
to
String layoutType = "Zeit";
no error occurs.
That is quite confusing, because both versions should have the same result.
The error message does not help me in any way.
Edit
I have compared the two possible variables like that:
String layoutType = theOscMessage.get(1).stringValue();
String layoutTypeB = "Zeit";
if(layoutType.equals(layoutTypeB)) println("Same String!");
Since gets printed to the console, both have to be the same … I really do not know where to search for an error anymore.
Edit 2
I have wrapped my second sketch in try {...} catch(Exception ex) {ex.printStackTrace();} like that:
void oscEvent(OscMessage theOscMessage) {
try {
if(theOscMessage.checkAddrPattern("/test")) {
if(debug && debugFeed) println("Received message from other sketch.");
String title = theOscMessage.get(0).stringValue();
String layoutTypeO = (String)theOscMessage.get(1).stringValue();
String layoutType = "Zeit";
if(debug && debugTemp) {
if(layoutType.equals(layoutTypeO)) println("IS DOCH GLEICH!");
}
if(debug && debugFeed) println("Parsed Information.");
if(debug && debugFeed) println("-----");
addToQueue(title, layoutTypeO);
}
} catch(Exception ex) {ex.printStackTrace();}
}
That gives me this error as result:
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(ArrayList.java:635)
at java.util.ArrayList.get(ArrayList.java:411)
at printer$Headline.useLayout(printer.java:260)
at printer$Headline.<init>(printer.java:188)
at printer.addToQueue(printer.java:407)
at printer.oscEvent(printer.java:395)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at oscP5.OscP5.invoke(Unknown Source)
at oscP5.OscP5.callMethod(Unknown Source)
at oscP5.OscP5.process(Unknown Source)
at oscP5.OscNetManager.process(Unknown Source)
at netP5.AbstractUdpServer.run(Unknown Source)
at java.lang.Thread.run(Thread.java:744)
Edit 4
Constructor for my Headline-Class:
class Headline {
//Define Variables
Layout layout;
String title, lastHeadline;
float yPos, speed;
float transparency = 255;
boolean fullyPrinted = false;
int boundingBoxHeight;
// Initialize Class Function
Headline(String t, float y, float s, String lay) {
title = t;
yPos = y;
speed = s;
layout = useLayout(lay);
boundingBoxHeight = calculateTextHeight(title);
}
You might want to know about useLayout() too, so here it is:
Layout useLayout(String name) {
ArrayList layoutVariants = new ArrayList<Layout>();
int existingLayouts = layouts.size();
Layout chosenLayout;
for(int i = 0; i < existingLayouts; i++) {
Layout currentLayout = (Layout)layouts.get(i);
if(currentLayout.layoutType == name) {
layoutVariants.add(currentLayout);
}
}
if(layoutVariants != null) {
int rand = (int)(Math.random() * layoutVariants.size());
chosenLayout = (Layout)layoutVariants.get(rand);
} else {
chosenLayout = (Layout)layouts.get((int)(Math.random() * existingLayouts));
}
return chosenLayout;
}

There are two problems with your code, and both of them are in your useLayout method.
The first problem is that you are not comparing Stringss correctly on this line:
if(currentLayout.layoutType == name) {
name is a String, and I assume currentLayout.layoutType is too. Two Strings that are equal but not the same will not compare equal under ==. As a result of this, your layoutVariants list will quite probably be empty at the end of the for loop.
This line should read:
if(currentLayout.layoutType.equals(name)) {
See also this question.
The second problem is that you don't correctly handle the case that the layoutVariants list is empty. The problem is on this line:
if(layoutVariants != null) {
layoutVariants will never be null, so the else branch of this if statement will never execute. Because layoutVariants.size() will be zero, rand will always be zero. Trying to get the element at index 0 in an empty ArrayList will give you precisely the IndexOutOfBoundsException you are seeing.
I imagine you want the else block to execute if the layout name given isn't recognised, in other words, if the layoutVariants list is empty, rather than null. In that case, change this line to
if(!layoutVariants.isEmpty()) {
Note the ! (not-operator) before layoutVariants. You want the code under the if statement to run if the layoutVariants element is not empty.
EDIT in response to your comments: a null ArrayList is very much not the same as an empty one. null is a special value meaning that the variable doesn't have an object of a given type.
Let's try a real-world analogy: a shopping bag. If you have an empty bag, or no bag at all, then you have no shopping either way. However, you can put things into an empty bag, and count how many items it contains, for example. If you don't have a bag, then it doesn't make sense to put an item in it, as there's no bag to put the item into. null represents the case where you don't have a bag.
Similarly, a String is a collection of characters, and the collection of characters can exist even if it doesn't contain any characters.
isEmpty() can be used for any collection, and, if you're using Java 6 or later, Strings as well. Off the top of my head I can't name any other classes that have an isEmpty method. You'll just have to consult the documentation for these classes to find out.
I've not worked with Processing much, but I am aware that Processing is built on Java, so I would expect any standard Java method to work. Also, I wouldn't worry about 'clearing' a variable: the JVM is generally very good at clearing up after you. There's certainly nothing I can see wrong with your code in this respect.
EDIT 2 in response to your further comment: ArrayList arr; declares a variable of type ArrayList. However, the variable arr is uninitialized: it does not have a value (not even null) and it is an error to try to read the value of this variable before you have assigned a value to it:
ArrayList arr;
System.out.println(arr); // compiler error: arr might not have been initialised.
Assign null and the code then compiles:
ArrayList arr = null;
System.out.println(arr); // prints 'null'.
It's not often you need to declare a variable and not give it a name, but one common case is where you want to assign different values to the same variable on both sides of an if statement. The following code doesn't compile:
int y = getMeSomeInteger(); // assume this function exists
if (y == 4) {
int x = 2;
} else {
int x = 5;
}
System.out.println(x); // compiler error: cannot find symbol x
The reason it doesn't compile is that each variable x is only available within the braces { and } that contain it. At the bottom, neither variable x is available and so you get a compiler error.
We need to declare x further up. We could instead write the following;
int y = getMeSomeInteger(); // assume this function exists
int x = 0;
if (y == 4) {
x = 2;
} else {
x = 5;
}
System.out.println(x);
This code compiles and runs, but the value 0 initially assigned to x is never used. There isn't a lot of point in doing this, and we can get rid of this unused value by declaring the variable but not immediately giving it a value.
int y = getMeSomeInteger(); // assume this function exists
int x;
if (y == 4) {
x = 2;
} else {
x = 5;
}
System.out.println(x);

Null Pointer that makes no sense to me?

Im currently working on a program and any time i call Products[1] there is no null pointer error however, when i call Products[0] or Products[2] i get a null pointer error. However i am still getting 2 different outputs almost like there is a [0] and 1 or 1 and 2 in the array. Here is my code
FileReader file = new FileReader(location);
BufferedReader reader = new BufferedReader(file);
int numberOfLines = readLines();
String [] data = new String[numberOfLines];
Products = new Product[numberOfLines];
calc = new Calculator();
int prod_count = 0;
for(int i = 0; i < numberOfLines; i++)
{
data = reader.readLine().split("(?<=\\d)\\s+|\\s+at\\s+");
if(data[i].contains("input"))
{
continue;
}
Products[prod_count] = new Product();
Products[prod_count].setName(data[1]);
System.out.println(Products[prod_count].getName());
BigDecimal price = new BigDecimal(data[2]);
Products[prod_count].setPrice(price);
for(String dataSt : data)
{
if(dataSt.toLowerCase().contains("imported"))
{
Products[prod_count].setImported(true);
}
else{
Products[prod_count].setImported(false);
}
}
calc.calculateTax(Products[prod_count]);
calc.calculateItemTotal(Products[prod_count]);
prod_count++;
This is the output :
imported box of chocolates
1.50
11.50
imported bottle of perfume
7.12
54.62
This print works System.out.println(Products[1].getProductTotal());
This becomes a null pointer System.out.println(Products[2].getProductTotal());
This also becomes a null pointer System.out.println(Products[0].getProductTotal());

You're skipping lines containing "input".
if(data[i].contains("input")) {
continue; // Products[i] will be null
}
Probably it would be better to make products an ArrayList, and add only the meaningful rows to it.
products should also start with lowercase to follow Java conventions. Types start with uppercase, parameters & variables start with lowercase. Not all Java coding conventions are perfect -- but this one's very useful.
The code is otherwise structured fine, but arrays are not a very flexible type to build from program logic (since the length has to be pre-determined, skipping requires you to keep track of the index, and it can't track the size as you build it).
Generally you should build List (ArrayList). Map (HashMap, LinkedHashMap, TreeMap) and Set (HashSet) can be useful too.
Second bug: as Bohemian says: in data[] you've confused the concepts of a list of all lines, and data[] being the tokens parsed/ split from a single line.
"data" is generally a meaningless term. Use meaningful terms/names & your programs are far less likely to have bugs in them.
You should probably just use tokens for the line tokens, not declare it outside/ before it is needed, and not try to index it by line -- because, quite simply, there should be absolutely no need to.
for(int i = 0; i < numberOfLines; i++) {
// we shouldn't need data[] for all lines, and we weren't using it as such.
String line = reader.readLine();
String[] tokens = line.split("(?<=\\d)\\s+|\\s+at\\s+");
//
if (tokens[0].equals("input")) { // unclear which you actually mean.
/* if (line.contains("input")) { */
continue;
}
When you offer sample input for a question, edit it into the body of the question so it's readable. Putting it in the comments, where it can't be read properly, is just wasting the time of people who are trying to help you.

Bug alert: You are overwriting data:
String [] data = new String[numberOfLines];
then in the loop:
data = reader.readLine().split("(?<=\\d)\\s+|\\s+at\\s+");
So who knows how large it is - depends on the success of the split - but your code relies on it being numberOfLines long.

You need to use different indexes for the line number and the new product objects. If you have 20 lines but 5 of them are "input" then you only have 15 new product objects.
For example:
int prod_count = 0;
for (int i = 0; i < numberOfLines; i++)
{
data = reader.readLine().split("(?<=\\d)\\s+|\\s+at\\s+");
if (data[i].contains("input"))
{
continue;
}
Products[prod_count] = new Product();
Products[prod_count].setName(data[1]);
// etc.
prod_count++; // last thing to do
}

beginner java, help me fix my program?

I am trying to make a calculator for college gpa's. I cut out all like 20 if statements that just say what each letter grade is. I fixed my first program for anybody looking at this again. The program now works, but regardless of the letters i type in the gpa it returns is a 2.0 . If anybody sees anything wrong it would be very much appreciated...again. Thanks
import java.util.Scanner;
public class universityGPA {
public static void main(String args[]){
int classes = 4;
int units[] = {3, 2, 4, 4};
double[] grade = new double[4];
double[] value= new double[4];
int counter = 0;
double total = 0;
double gpa;
String letter;
while(classes > counter){
Scanner gradeObject = new Scanner(System.in);
letter = gradeObject.next();
if(letter.equalsIgnoreCase("A+") || letter.equalsIgnoreCase("A")){
grade[counter] = 4;
}
if(letter.equalsIgnoreCase("F")){
grade[counter] = 0;
}
value[counter] = grade[counter] * units[counter];
counter++;
}
for(int i = 0; i < classes; i++ ){
total += value[i];
}
gpa = total/classes;
System.out.println("You gpa is " +gpa);
}
}

You forgot to initialize grade. The NullPointerException is telling you that grade is null. The exception is thrown the first time you try to use grade, in the statment grade[counter] = 4;. Allocate as much space as you need with new.

Initialization of grade can be done statically as well dynamically:
double []grade = new double[4];
or
double []grade = new double[classes];
Do the same for value as well.

Here are a few pointers for cleaning up your code:
Try to be more consistent with your formatting. Make sure everything is properly indented and that you don't have lingering spaces at the beginnings or endings of lines (line 18).
You should declare variables as close to the first spot you use them as possible. This, along with making your code much more readable, minimizes the scope. For instance, on line 18, you initialize letter, but it is never used outside the scope of the while statement. You should declare the variable right there, along with the initializer (String letter = gradeObject.next()).
Declaring arrays in the type name[] form is discouraged. It is recommended to use the type[] name form instead.
Try to separate your program into distinguished sections. For instance, for this program, you can clearly see a few steps are involved. Namely, you first must grab some input, then parse it, then calculate the return value. These sections can be factored out into separate methods to clean up the code and promote reuse. While it may not seem to yield many benefits for such a simple program, once you start working on larger problems this organization will be absolutely mandatory.

NullPointerException means you are trying to access something that does not exist.
Since your grade[] is null, accessing it on line 21 by grade[counter] actually means you are accessing something that has yet to be created.
You need to initialize the array, so it actually has an instance.