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);
Related
int i = 3;
int j = 2;
int k = 1;
Printer printer = new Printer();
if (printer.getTotalAmount() > 0) {
if (printer.getType().equals("canon")) {
if (i >= j) {
i = i-j; // i=3-2, so i will be 1 now
}
}
if (printer.getType().equals("epson")) {
if (i >= k) {
i = i - k; // it should be i = 1-1 and i will be 0 now
}
}
}
My problem is that the variable i's value is not updated after the previous if statement. Due to block scope, the variable i's value is still 3.
How can I solve this problem?
Your two if statements represent mutually-exclusive conditions. The printer's type can be "canon" OR it can be "epson". Never both. So only one of your two if conditions will be met, and only one of the two code blocks will be executed.
Say, for example, that your Printer's type is "epson". When the first condition is evaluated, it will check whether "epson" is equal to "canon". Since they are not equal, the condition evaluates to false and all of the code inside of your if () {/* code */} block is completely skipped.
Your theory behind the scope causing the issue isn't accurate: since the variable is declared outside of the if block, the updated value will be reflected in every location that has access to that variable.
You need to update your logic to account for the fact that only one of the scenarios will occur or, if this is just a code simplification, find a more appropriate scenario analogous to your real code.
It may be helpful to review Oracle's tutorial on the if statement if this still isn't clear.
I think you should add debug statements to know more about flow of your program
becuase you didn't mention the value of printer.getTotalAmount() and printer.getType()
on which value of i is depend.
e.g.
System.out.println("Total Amount:"+ printer.getTotalAmount());
if (printer.getTotalAmount() > 0) {
System.out.println("Type:"+ printer.getType());
if (printer.getType().equals("canon")) {
System.out.println("inside if canon");
if (i >= j) {
i = i-j; // i=3-2, so i will be 1 now
}
}
if (printer.getType().equals("epson")) {
System.out.println("inside if epson");
if (i >= k) {
i = i - k; // it should be i = 1-1 and i will be 0 now
}
}
}
I apologize in advance, I am a java noob.
I have this in a statement
if(a==0 && b<4)
{
value = ((elev[a][b]-elev[a+1][b])*0.00001* double "variable" ) ;
}
So my main question is would the following....
(elev[a][b]-elev[a+1][b])
return an int value (assuming that the array was initialized and populated with int values, and that for a==0 and b<4 none of the references are null.
Sorry in advance if this is silly. Please don't feel inclined to comment, but help would be appreciated. I haven't done a lot of this java stuff.
When i populated the array, I printed it's contents to make sure I was populating correctly, and everything is where it should be...
Alas, I get a null pointer error wherever that (elev[a][b] - elev[a+1][b]) is first referenced....yet i know that the values are being put there.
Next question. When i populate an array, if i want to reference the values,
while(input.hasNextInt())
{
elev[i][j] = input.nextInt(); <-- this is how i was doing it
}
of elev[][]... do i need to say
elev[i][j] = new input.nextInt();
or is how i was doing it sufficient. When i populated an ArrayList from a file I had to use the "new" prefix So i was trying to figure out why i would get a null there.
Like i said I did print the array after reading it from the file and it printed out everything was in its place.
Thanks everyone.
EDIT
ok sorry for simplicity sake i didn't put in the actual code of "value"
it is actually
double randKg = getRandKg(avgKgNitrogen[z]);
double gradient = 0.00001
double under = ((randKg *(elev[a][b] - elev[a+1][b]) * gradient));
2nd Edit
This is the code for how i populated.
try{
File file = new File(filename);
Scanner input = new Scanner(file);
int rows = 30;
int columns = 10;
int elev[][] = new int[30][10];
for(int i = 0; i < rows; ++i){
for(int j = 0; j < columns; ++j)
{
while(input.hasNextInt())
{
elev[i][j] = input.nextInt();
}
}
}
input.close();
}
catch (java.io.FileNotFoundException e) {
System.out.println("Error opening "+filename+", ending program");
System.exit(1);
}
3rd edit
So i am getting the null pointer here.....
(elev[a][b] - elev[a+1][b]) > 0 )
Which is why i originally asked. I have printed the array before when i populated and everything is where it should be.
You are getting a null pointer exception because double "variable" does not indicate to any integer or double value. Compiler is just trying to convert String 'variable' into double which is not possible. So, try eliminating the Double Quotes from "variable". Moreover you have not declared the data type of value variable.
Ignoring other problems in your code (covered by other answers), here's about your actual question:
If the code
if(a==0 && b<4) {
value = (elev[a][b] - elev[a+1][b]);
}
crashes with NullPointerException, it means elev is null. Assuming a and b are of type int, then there is no other way this can generate that exception (array out of bounds exception would be different). There are two options for the cause:
You execute above code before you do int elev[][] = new int[30][10];, so that elev still has the initial null value.
elev in the crashing line is a different variable than elev in initialization shown in the question.
And in you code, it seems to be 2. You create local elev in the initialization. It goes out of scope and is forgotten. You probably should have this initialization line in your method:
elev = new int[30][10];
And then you should have a class member variable instead of local variable in a method:
private int[][] elev;
Ok so I am new to programming(Don't laugh at me if I ask a question very easy).
A sample of my code is as follows:
public int calcGCF(int mya, int mye, int myf, int myj)
{
x = myj * myf;
y = mye* mya;
while(x != 0 && y != 0)
{
if(x % y == 0)
{
remainder = y;
}
int gcf;
gcf = y;
y = x % y;
x = gcf;
}
}
Ok. So what this code is for is to potentially solve the derivative of any problem that the user inputs. Part of solving the derivative is getting a gcf of 2 numbers and factoring it out. When I try to compile this code, it says that I am missing a return statement. I understand what that is, but when I try to say "return remainder;" it says it may not have been initialized. Can somebody please tell me what I am doing wrong in this code, and help me with what I should put in my return statement? Thank You! By the way this is with java code.
Where are the variables x, y, and remainder declared? I don't see an int remainder; statement anywhere in the code you posted. There's also no return statement in the method, so it will not compile.
Local variables (variables that you declare inside a method) must be initialized with a value before you use them anywhere where you read the value. If you do this, for example:
public int method(int a) {
int value;
if (a > 10) {
value = 99;
}
return value;
}
Then you will get the same error as you are getting, because in case a is not greater than 10, the variable value isn't assigned any value when you reach the return statement - so Java doesn't know what value to return then.
You must make sure that value is assigned a value in any possible case.
As you wish you can return the remainder. Just initialize your remainder to a value. eg: remainder=0;
I understand what that is, but when I try to say "return remainder;" it says it may not have been initialized.
So you simply need to declare, at the top of your code, something like:
remainder = 0;
I would also think about naming your variables a little more appropriately than just myj.
I get the error message cannot find symbol, symbol: method books(int[], int) when I try to compile the following code.
For further explanation about what I want the code to do, see below the code.
public class books {
public void main(String[] args) {
int searchValue = 0, index;
int refNum[] = new int[4]; // the array
refNum[0] = 4; //numbers to refer to (aka to find)
refNum[1] = 6;
refNum[2] = 10;
refNum[3] = 12;
refNum[4] = 14;
int input = Integer.parseInt(enterValue.getText()); //takes user's input
for (int x = 0; x < refNum.length; x++) {
refNum[x] = input; //Tells refNum value to be
}
searchValue = input;
index = books(refNum, searchValue); //"books" is underlined
if (index != -1) {
binarySearchField.setText("We found: " + index);
} else {
binarySearchField.setText("Sorry! Not Found!");
}
public static Boolean binarySearch(String [] refNum, int left, int right, String search){
//Boolean code for later
}
This program uses binary search to find values stored in array after user inputs number, if they match then the item is successfully found. User inputs desired number in 'enterNumber' which is a TextField. Now in my code )which I'm 78% sure will work if it wasn't for this one little thing) there is an all important that is underlined which shouldn't be, (I've commented beside the line to show)
Now I had thought I was suppose to put the class name there, but apparently since it is underlined that is not the case. Any ideas on what I should be putting there in it's place?
And I apologize for the question may be a bit misleading on what I'm really asking, I just wasn't sure how to word the question.
The line
index = books(refNum, searchValue);
seems to be underlined because you have no method called books that takes an int[] and an int as arguments in your books class definition.
Now I had thought I was suppose to put the class name there Why do you assume you have to put the class name there? Figure out what you are trying to do with this code and then you will understand what goes in that line (at least in pseudocode).
Also it seems like you have a method declared directly inside another method. That is not legal in java. If this is not the case, please show us correct code.
books is your class's name..that might be the reason you are getting this error. You can't call constructor like a method. Change class's name to Books or something else..or change method's name
I have a method that gets returns a type SENSOR
In the bold is where I am getting a runtime NullPointerException, cannot understand why.
public Sensor getSensorAt(int x,int y,GridMap grid)
{
/*go through sensor storage array
* for eachsensor index call the get x get y method for that
* compare it to the x,y of the robot
*
*/
for(int i=0;i<s1.length;i++){
if(s1[i].getX() == x){ <======= NullpointerException
if(s1[i].getY()== y){
return s1[i];
}
}
}
return null;
}
You did not show us where s1 is created, but it looks like s1 does not have anything in it for some index i.
I tend to write my for loops like so to make code like this a bit cleaner
Object result = null;
for(int i=0;i<s1.length;i++){
Object current = s1[i]; // Replace Object with whatever your array actually contains
if(current.getX() == x && current.getY() == y) {
result = current;
break; // if you only need the first match
}
}
return result;
Things like formatting are important and will help you prevent bugs in the first place, and make them easier to find when they do happen....
Some of the elements in the array s1 is null, and when you are trying to invoke a method on that null object you are getting NPE.
Hope it helps you.