Develop Reference

Values are not initializing under try block?

trying to make program rotation of array, it was giving an Exception by user misinput so I use try block but now, under try block it is not initializing values....
Can some one tell the reason or solution for this....
public static void main (String[] args) {
Scanner sc = new Scanner(System.in);
ArrayRotation ar = new ArrayRotation();
System.out.println("Enter T : ");
int t = sc.nextInt();
sc.nextLine();
while(t!=0){
System.out.println("\nEnter N D : ");
String s = sc.nextLine();
s.trim();
String st[] = s.split(" ");
int n,d;
try{
n = Integer.parseInt(st[0]);
d = Integer.parseInt(st[1]);
}catch(Exception e){ System.out.println("Exception"+e.getMessage()); }
System.out.println("Enter Element : ");
s=sc.nextLine();
st = s.split(" ");
ar.rotateArray(st,n,d);
t--;
}
}

If you need valid input and you did not get valid input, the thing to do is to try again to get valid input, after telling the user the input was invalid. Don't just proceed with the invalid data. You therefore need an inner loop:
while (t!=0) {
boolean validInput = false;
while (!validInput) {
System.out.println("\nEnter N D : ");
String s = sc.nextLine().trim();
String[] st = s.split(" ");
int n,d;
try {
n = Integer.parseInt(st[0]);
d = Integer.parseInt(st[1]);
validInput = true;
}
catch (Exception e) {
System.out.println("Invalid input");
}
}
… process n and d as before …
}
For my taste the loop to get the valid input would be better off being a subroutine in its own right - for clarity.

Variable in local scope should be initialized , that is what error , so do initialize the variables n and d to some integer value say as below
int n = 0 ,d = 0;
try{
n = Integer.parseInt(st[0]);
d = Integer.parseInt(st[1]);
}

When a method throws an exception, that method never returns.
This means that if n = Integer.parseInt(st[0]); throws an exception, it does not return a value, which means n will not be assigned a value (since there is no return value to assign to it).
You are ignoring the exception and trying to continue as if nothing went wrong. But something did go wrong—n was never assigned a value. So the compiler tells you that it is not safe to use n in any subsequent code.
To solve this, you first must decide what to do if the user provides invalid input. You can’t just ignore the exception. If the input doesn’t represent two integers, you don’t have any values to work with. You can’t continue in any meaningful way.
The best course of action is to remove your try and catch. This will cause the program to terminate if Integer.parseInt fails, which is almost certainly what you want (unless your assignment requires you to do something different). Remember that it is not possible to continue in any meaningful way without values assigned to n and d.
In other words, change this:
int n,d;
try{
n = Integer.parseInt(st[0]);
d = Integer.parseInt(st[1]);
}catch(Exception e){ System.out.println("Exception"+e.getMessage()); }
to this:
int n = Integer.parseInt(st[0]);
int d = Integer.parseInt(st[1]);
As a side note, this line does nothing:
s.trim();
…because Strings cannot be changed. s.trim() returns a new String which you must capture in a variable. You probably want to do this:
s = s.trim();

Your image is quite misleading and really doesn't point to the actual problem, it only points to what you perceive to be the problem. Your mistake was placing the initialization of variables n and d into a try block which takes your call to the rotateArray() method out of scope for that initialization of those variables.
The bigger problem is... What in the world are you rotating? Where is the Array to rotate? Is it actually a String Array or is it suppose to be an Integer Array? Please don't tell me it's the st[] String Array (which is what you're trying to do) because according to your code that array is used to establish the array size (n) portion to work with and the number of elements (d) the User wants to rotate by. No rocket science to rotate an Array with only two elements. Give the rotateArray() method an array to actually rotate.
Let's provide an Integer Array and a way to do this without a try/catch mechaism:
// The Array to carry out rotations on.
int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
String ls = System.lineSeparator();
Scanner sc = new Scanner(System.in);
ArrayRotation ar = new ArrayRotation();
int t = 0;
String value = "";
while (value.equals("")) {
System.out.print("Enter Number of times to Rotate Array: --> ");
value = sc.nextLine().trim();
/* Make sure a String representation of a Integer value is supplied.
The regular Expression "\\d+" in the String#matches() method
ensures the a numerical integer string is supplied. */
if (!value.matches("\\d+" || value.length() > 9) {
/* Will handle situations where nothing is supplied, alpha
characters might be supplied, or the supplied numerical
value is outrageously large. */
System.out.println("Invalid integer numerical value supplied!" + ls);
value = "";
}
}
t = Integer.parseInt(value);
while (t != 0) {
System.out.println();
System.out.print("Enter the Size (portion) of the Array to consider and the" + ls
+ "number of elements to rotate (separated with a space): --> ");
String s = sc.nextLine().trim();
// Quit if anything starting with the letter "Q"
// (like "q" or "quit") is supplied.
if (s.substring(0, 1).equalsIgnoreCase("q")) {
System.out.println("\"Quit\" Supplied!");
System.exit(0);
}
String st[] = s.split(" ");
/* Make sure two values were supplied and that
they are both numerical integer strings. */
if (st.length != 2 || !st[0].matches("\\d+") || !st[1].matches("\\d+")) {
System.out.println("Invalid Input! Try again and make sure 'both' "
+ "values are numerical Integers.");
continue;
}
// Declare and initialize the n and d variables.
int n = Integer.parseInt(st[0]);
int d = Integer.parseInt(st[1]);
/* If the number of elements to rotate is greater
than the portion of array to rotate in. */
if (d >= n) {
System.out.println("Invalid Input! The size of the Array portion to rotate" + ls
+ "must be greater than the number of elements to rotate.");
}
/* If the supplied Array size to deal with is
out of bounds of the Array itself. */
else if (n < 1 || n > array.length) {
System.out.println("You have supplied an invalid Array Size! (" + n
+ ") Size must be between 1 and " + array.length + "!"
+ ls);
}
/* If the supplied number of elements to rotate
is less than 1 or greater than the total number
of elements - 1. */
else if (d < 1 || d > (array.length - 1)) {
System.out.println("You have supplied an invalid number of elements to rotate! (" + d
+ ") Value must be between 1 and " + (array.length - 1) + "!" + ls);
}
// All is good - Do the rotation.
else {
ar.rotateArray(array, n, d); // Rotate the Array
// Display the current rotation...
System.out.println("Current Rotation: --> " + Arrays.toString(array));
t--;
}
}
// Done
The error you outline in your image is a general compilation error and is relatively generic for all data types. This error occurs when you are trying to use a local variable without first initializing it. You won't get this error if you use a uninitialized class or instance variable because they are initialized with their default value (for example: Reference types are initialized with null and integer types are initialized with zero), but if you try to use an uninitialized local variable in Java, you will get this error. This is because Java has the rule to initialize the local variable before accessing or using them and this is checked at compile time. If the compiler believes that a local variable might not have been initialized before the next statement which is going to use it, you will receive this error. You of course will not get this error if you just declare the local variable but don't use it but then, why declare it in the first place.
Everyone is stating to initialize the local variables n and d because in reality, in order to successfully compile your code that is exactly what needs to be done in order for the rotateArray() method (which uses these uninitialized variables) to function. Again in reality, you do initialize them however your code does it within a try{} block which alters scope and the compiler is smart enough to know that if the initialization fails within the try{} block then the catch{} block could let that failure be ignored. In fact, if you were to place the call to the rotateArray() method within that try{} block then you would not get this compile time error since the call is within the scope of of where the variables n and d are actually initialized. You know, a decent IDE (line Eclipse, NetBeans, InteliJ, etc) should catch this error for you long before you try to compile.
According to your code, the actual intent of the try/catch blocks would be to handle the case of invalid input whereas a non-numerical integer value was supplied by the User. In this case it would be up to your catch{} block to handle that particular situation which should be to inform the User of the invalid input and then continue to re-prompt for proper input. At compile time the compiler really doesn't care about this mechanism since this would be a Runtime Error unless of course it is syntax related.
Nothing wrong with try/catch, I just like to avoid them if I can.

Android/Java using two dimensional array to create chatbot

public class ChatBot {
String[][] chatBot={
// standard greetings
{ "hi", "hello", "hey" }, { "hi user"},
// question greetings
{ "how are you" }, { "good"},
// default
{ "I did not understand. Please try something else" }, };
public ChatBot() {
}
public String checkAnswer(String message) {
byte response = 0;
int messageType = 0;
String x = null;
List temp;
int cblength = chatBot.length - 1;
while (response == 0 && messageType <= cblength) {
temp = Arrays.asList(chatBot[messageType]);
if (temp.contains(message)) {
response = 2;
x = chatBot[(messageType) + 1][0];
}
messageType = messageType + 2;
if (response == 1)
x = chatBot[chatBot.length - 1][0];
}
}
return x;
}
I created this simple chatbot to test my chat application. It uses a two dimensional String Array to save the possible inputs and outputs. The checkAnwer method receives the user input and is supposed to return the correct output. It uses a while loop to check the input fields and return the corresponding output, if the content of the field matches with the array. If the loop reaches the end of the array, it is supposed to return the default answer. The first group of inputs (hi/hello/hey) returns the right output(hi user), but every other input causes the while-loop to exceed the array length.
Edit
I removed the error in the Code, all inputs are now accepted, non valid inputs return null.
Edit2
I changed int cblength = chatBot.length - 1;
to
int cblength = chatBot.length;
and messageType = messageType + 2;
to
if ((messageType+2)>=cblength)
{
response=1;
}
else {
messageType = messageType + 2;
}
The code is now working properly.

If I'm understanding your code correctly, chatBot has a length of 5. On each full pass of the while loop, messageType is incrementing by 2. This means that on the second pass, messageType = 2. This means that on the following line :
x = chatBot[(messageType * 2) + 1][0];
We are looking for (2*2)+1 = 5 as an index. As the list is of length 5, the max index is 4, causing the IndexOutOfBoundsException.
There are two main ways I could see to fix this:
Reconsider whether you really need to repeat the same block of code twice in the while loop - this adds a bit of unneeded complexity, and reduces how often the while conditions are checked.
Update the while condition to check that any (messageType*2)+1 which will occur during the iteration will still be within the bounds of the array.

Removing a substring from a string, repeatedly

Problem:
Remove the substring t from a string s, repeatedly and print the number of steps involved to do the same.
Explanation/Working:
For Example: t = ab, s = aabb. In the first step, we check if t is
contained within s. Here, t is contained in the middle i.e. a(ab)b.
So, we will remove it and the resultant will be ab and increment the
count value by 1. We again check if t is contained within s. Now, t is
equal to s i.e. (ab). So, we remove that from s and increment the
count. So, since t is no more contained in s, we stop and print the
count value, which is 2 in this case.
So, here's what I have tried:
Code 1:
static int maxMoves(String s, String t) {
int count = 0,i;
while(true)
{
if(s.contains(t))
{
i = s.indexOf(t);
s = s.substring(0,i) + s.substring(i + t.length());
}
else break;
++count;
}
return count;
}
I am just able to pass 9/14 test cases on Hackerrank, due to some reason (I am getting "Wrong Answer" for rest of the cases). After a while, I found out that there is something called replace() method in Java. So, I tried using that by replacing the if condition and came up with a second version of code.
Code 2:
static int maxMoves(String s, String t) {
int count = 0,i;
while(true)
{
if(s.contains(t))
s.replace(t,""); //Marked Statement
else break;
++count;
}
return count;
}
But for some reason (I don't know why), the "Marked Statement" in the above code gets executed infinitely (this I noticed when I replaced the "Marked Statement" with System.out.println(s.replace(t,""));). I don't the reason for the same.
Since, I am passing only 9/14 test cases, there must be some logical error that is leading to a "Wrong Answer". How do I overcome that if I use Code 1? And if I use Code 2, how do I avoid infinite execution of the "Marked Statement"? Or is there anyone who would like to suggest me a Code 3?
Thank you in advance :)

Try saving the new (returned) string instead of ignoring it.
s = s.replace(t,"");
replace returns a new string; you seemed to think that it alters the given string in-place.

Try adding some simple parameter checks of the strings. The strings shouldn't be equal to null and they should have a length greater than 0 to allow for counts greater than 0.
static int maxMoves(String s, String t) {
int count = 0,i;
if(s == null || s.length() == 0 || t == null || t.length() == 0)
return 0;
while(true)
{
if(s.contains(t) && !s.equals(""))
s = s.replace(t,""); //Marked Statement
else break;
++count;
}
return count;
}

You might be missing on the edge cases in the code 1.
In code 2, you are not storing the new string formed after the replace function.
The replace function replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
Try this out:
public static int findCount(String s, String t){
if( null == s || "" == s || null == t || "" == t)
return 0;
int count =0;
while(true){
if(s.contains(t)){
count++;
int i = s.indexOf(t);
s = s.substring(0, i)+s.substring(i+t.length(), s.length());
// s = s.replace(t,"");
}
else
break;
}
return count;
}

String r1="ramraviraravivimravi";
String r2="ravi";
int count=0,i;
while(r1.contains(r2))
{
count++;
i=r1.indexOf(r2);
StringBuilder s1=new StringBuilder(r1);
s1.delete(i,i+r2.length());
System.out.println(s1.toString());
r1=s1.toString();
}
System.out.println(count);

First of all no logical difference in both the codes.
All the mentioned answers are to rectify the error of code 2 but none told how to pass all (14/14) cases.
Here I am mentioning a test case where your code will fail.
s = "abcabcabab";
t = "abcab"
Your answer 1
Expected answer 2
According to your code:
In 1st step, removig t from index 0 of s,
s will reduce to "cabab", so the count will be 1 only.
But actual answer should be 2
I first step, remove t from index 3 of s,
s will reduced to "abcab", count = 1.
In 2nd step removing t from index 0,
s will reduced to "", count = 2.
So answer would be 2.
If anyone know how to handle such cases, please let me know.

Java: If statement not working?

Awnsers below worked, thanks guys!
boolean Again = true;
while (Again = true)
{
String input = JOptionPane.showInputDialog(null, "Input Za Number");
try
{
int input2 = Integer.parseInt(input);
int R1 = 1;
int R2 = 1;
while (R2 < input2)
{
R1 = R1 * 2;
R2 = R2 + 1;
JOptionPane.showMessageDialog(null, R1);
}
String Ag = JOptionPane.showInputDialog(null, "Do it again? (Y/N)");
if (Ag.equals("N"))
{
Again = false;
}
}
catch(Exception e)
{
JOptionPane.showMessageDialog(null, "What is '" + input + "'?!?! Enter an actual number.");
}
}
I put the part thats not working as I hope in bold. Its the "if (Ag.equals("N"))". Im trying to make it so if a user inputs "N", then the program will stop running. Otherwise it will loop and keep going. Problem is, even if I type N, it will loop. I am getting no errors. Please help, I am much confuse :(

This is a prime example as to why professional developers will always use
if ( null == object )
over
if ( object == null )
In the event of a mistype, such as the following
// as posted
while ( Again = true ) // works, always true
// the other way
while ( true = Again ) // compiler error
the way as posted would be reassigning the value true to Again every time the loop is reiterated; if the statement had been written the other way, the compiler would have thrown an error, stating that you can not assign a value to true.
With just the single equals, you are reassigning the value of Again to true every time you get here, where as the double equals checks for equality.
In a case such as this, you really don't even need the true, you could simply be using
while ( Again )
// or again
while ( true == Again )
relevant

When you do something like
while (Again = true)
you are actually assigning the variable to true,
that is making your while infinite...
Do instead
while (Again) // since is boolean you dont need to compare against a true value..

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);