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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.

How to add a variable to another variable that's already set

My homework is to create a program that takes a list of numbers and prints out the highest number divisible by four.
List would look like this:
12
16
87
58
25
73
86
36
79
40
12
89
32
Input should be:
40 because it is the highest number there divisible by four.
Here is my code:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int saved = 0;
int saved2 = 0;
for (int i = scanner.nextInt(); i % 4 == 0; i = scanner.nextInt()) {
for (boolean bull = true; bull == true; bull ^= true) {
if (i > saved) {
saved -= saved2;
saved += i;
saved2 += i;
}
}
System.out.println(saved);
}
}
}
The input of my code is
12
16
I don't really understand why this is doing it, but it seems to me that I'm adding the variables wrong. The homework page on adding variables does not specify how to add variables to each other.
Does anyone have a tip to improve the code in anyway, or find a way to make a fix my code? Thank you.

welcome to Java.
First you are saying you got input, but that is output. Input is what you enter, and output is what you get printed.
Then there is a mistake in your for loops. You have too much going on in one place. By the logic which is implemented, your program will exit first level for loop whenever your entered value is not divisable by 4.
Read on for loops if you want to learn more https://www.learnjavaonline.org/en/Loops.
I recommend to start from while loops instead. The logic whould be this:
1. create variable to hold the correct answer saved
2. create another one to hold the value read from console i
3. start the while loop with condition i = scanner.nextInt()
3.1 check if the value just entered i is divisable by 4
3.2 if it is, then compare if it's larger than the one was saved before (initially saved value will be 0)
3.3 if it is larger, then assign the read value i to the saved
4. At the end of the loop, you will have the highest number divisable by four in your saved variable. Print it.

I will provide some help, according to
How do I ask and answer homework questions?
for (int i = scanner.nextInt(); i % 4 == 0;i = scanner.nextInt())
This only reads as long as ALL inputs are divisible by 4, that is why it ends at 16, because 87 is not divisible by 4.
for (boolean bull = true; bull == true ;bull ^= true)
This needs explanation by you, but I am pretty sure that it unconditionally executes the body of the inner loop exactly once. (Not 100% sure, because the representation of true and false could be weird in your machine. Should 0 be the representation of true, i.e. really weird, then it is an endless loop, which does not match the output you describe...)
System.out.println(saved);
This executes exactly once per input, except the last one, which is not a multiple of 4.
The value of saved is identical to input, as long as it is increasing.
These hints explain the unexpected output.
If you inspect the details of what the problem is, you should be able to improve your coding attempt.

This is how I super-quickly fixed in your code.
Note that there are no statements about the possible minimum value and about how do you stop the input. Therefore the solution is pretty-straightforward, it just reads the input until integers are present there.
This article may be useful about handling the input from the Scanner.
I hope the comments in the code will help. Add comments if there are any questions. Good luck!
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int currentMax = Integer.MIN_VALUE; // you may set negative or 0 if you know that all the input is positive
// int saved2 = 0; // no need for this variable
while (scanner.hasNextInt()) { // you can make a better input handling, especially if you know when it should end the input. Now it will end on any non-integer input line
int i = scanner.nextInt();
// for (int i = scanner.nextInt(); i % 4 == 0; i = scanner.nextInt()) {
// for (boolean bull = true; bull == true; bull ^= true) {
if (((i % 4) == 0) && (i > currentMax)) {
currentMax = i;
// saved -= saved2;
// saved += i;
// saved2 += i;
// }
}
}
System.out.println(currentMax); // moved out of "for" or "while" cycles. Print the value after the input has ended.
}
}

using a while loop for user to input multiple int and find the max and min

so my homework question is prompt user a series of integers and find the max and min of those integer. Use a loop and -99 to break loop.Below is my code but my question is that is there a shorter way for this? feel free to comment and i appreciate your time reading this.
Scanner input=new Scanner(System.in);
int num1,num2,max,min;
System.out.print("enter a number: ");
num1=input.nextInt();
System.out.print("enter another number: ");
num2=input.nextInt();
max=Math.max(num1,num2);
min=Math.min(num1,num2);
while (num2!=-99){
System.out.print("enter a number or -99 to stop: ");
num2=input.nextInt();
if(num2!=-99){
max=Math.max(max,num2);
min=Math.min(min,num2);
}
}
System.out.println("largest is: "+max);
System.out.println("Smallest is: "+min);

You check for the condition of num2 != -99 twice, remember the first rule of programming, do not repeat yourself
You could save some lines by checking for min and max before asking for the next input. This way you do not need to check if num2 != -99 inside the while loop

Ok So after working on this. I finally did it. It does have a small bug, but I really don't wanna fix it so if anyway wants to edit this then be my guest.
Scanner input = new Scanner(System.in);
int studentNum = 0;
ArrayList<Integer> calc = new ArrayList<Integer>();
while (studentNum <= 100) {
System.out.print("Enter a number: ");
calc.add(input.nextInt());
studentNum += 1;
if (input.nextInt() == -99) {
break;
}
}
int min = Collections.min(calc);
int max = Collections.max(calc);
for (int i = 0; i < calc.size(); i++) {
int number = calc.get(i);
if (number < min)
min = number;
if (number > max)
max = number;
}
System.out.println("Max is " + max);
System.out.println("Min is " + min);
This does exactly what you want. However, there was a problem checking for the exit signal.
if (input.nextInt() == -99) {
break;
}
this checks if the userInput is equal to -99 then stops the program and calculates and prints out the min and max. However the tiny bug is that it will first ask for your number to add to the array list and then it will ask again for the userInput to check if its equal to -99. But overall it does exactly what you want.
Hope this helped.
EDIT I will work on it later and find a way to fix that bug if no one else knows.

Your code has one minor bug and can be slightly optimised. Things you might want to consider:
What happens (and what should happen) when the user types -99 as the second number?
Do you necessarily need to have at least 2 numbers? Wouldn't one be enough for the program to exit gracefully? The first number would then be both min and max.
Can you re-order your code lines so that the duplicated (num2!=-99) is not necessary anymore?
Pro questions:
What happens if the user types in some letters? How can you handle that case?
What happens if the user types in a super high number (bigger than the maximal integer)?
What happens if the user presses enter without typing any number?
Nitpicking:
Using + to concatenate strings and numbers is a bad idea because it's hard to remember where it works and where it doesn't.
Better look into String.valueOf(int i) and String.format(String format, Object... args)
Look up Google's Java Coding Style for formatting your code in best readable way. In many editors you can automatically apply the style. It describes things like where to use spaces or what to indent.

Breaking out" of a while loop still executing whats inside?

The purpose of this program is to take in positive integers and once the sentinel value (-1) is hit the program will return the 2 lowest numbers. My program works, but in some scenarios it doesn't. for example if I enter 10,15,20,-1 the program will result in 10 rather than 10 and 15. Here is my program:
public class Small{
public static void main(String [ ] args){
int number;
number=IO.readInt();
int lowest=number;
int lowest2=number;
while (number!=-1){
number=IO.readInt();
if(number>0){
if(number<lowest && number!=-1){
lowest=number;}
else{if((number<lowest2||!(number>=lowest2))&& number!=-1){
lowest2=number;}
}
}
}
IO.outputIntAnswer(lowest);
IO.outputIntAnswer(lowest2);
}
}

The main problem with your code is that you set lowest and lowest2 to the first value you enter. If all the other numbers you enter are higher than the first number, it will never be able to find anything lower.
With your example, the first number is 10 which you assign to lowest and lowest2. When you enter 15, it's not lower than 10, so neither variable can be reset. Same with 20.
You've also got a lot of redundant checks in your if-statements.
public class Small {
public static void main(String [ ] args) {
int number;
int lowest = Integer.MAX_VALUE;
int lowest2 = Integer.MAX_VALUE;
while (number!=-1) {
number=IO.readInt();
if (number > 0) {
if(number < lowest) {
lowest=number;
}
else if (number < lowest2) {
lowest2=number;
}
}
}
}
IO.outputIntAnswer(lowest);
IO.outputIntAnswer(lowest2);
}

The problem is with your logic flow of the program. Here's what the code is doing:
Read in one number, store in both lowest and lowest2.
Go through loop to read in more numbers
2a. If the number is positive, check against lowest.
2a1. If the read in value is lower than lowest, change lowest's value to the read in value.
2a2. Otherwise, if the read in value is lower than lowest2, change lowest2's value to the read in value. Only do this if lowest was not changed.
2b. If the read in value is -1, end the loop.
2c. If the read in value is negative but not -1, continue but don't add the number to lowest or lowest2.
Print out the values for lowest and lowest2.
If you see the error, it's in 2a2. This is linked to the fact that your setup before the while loop is formatted as you did: you made both lowest and lowest2 that first value.
This code would normally run correctly, except for one instance: what if that first value were to be the smallest positive value you entered, with all other values greater than it? lowest2 would be set to that value, and you're checking to see if any other values are smaller than it (which they're not, because they're all going to be greater than it).
Tips for when you're coding:
1) Attempt to develop a logical thinking mentality. Think through how you want to create algorithms for your program. Make sure you don't run into any situations where your program does not run the way you want it to, like in this case (this is called a logic error).
2) Run through your programs by hand when you're finished coding, or after you've run it and got an error. Step through every line of your code, and try to see where and why your code isn't working the way you want it to. Or have someone else see, like a fellow programmer. Sometimes, even the best eyes do not catch their own mistakes.
EDIT:
There are various ways to solve this particular problem. One way is to do what Seeker and Rick did:
1) Set both values to the largest possible Integer value, and thus all values entered will be lower than the first values.
2) Ask for the first two inputs at the beginning before the loop, and check them against each other to set the first two lowest values.
However, I believe there are certain things to watch out for when you're doing something like this. These should all be outlined before you code, of course.
1) What if the user is entering only one or zero valid values? Seeker's method wouldn't work, unless he checks that the first/second value is negative/-1. Rick's method wouldn't work either because at least one of the lowest/lowest2 values would still be that max Integer value.
2) What if there were no positive values entered before the -1? This is similar to number 1, and your ints would be null.
You can certainly use Seeker's and Rick's algorithms, but you should check for these conditions if you use them.

import java.util.Scanner;
public class Small {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter Number");
int lowest = scanner.nextInt();
System.out.println("Enter Number");
int lowest2 = scanner.nextInt();
if (lowest > lowest2) {
int t = lowest;
lowest = lowest2;
lowest2 = t;
}
while (true) {
System.out.println("Enter Number");
int number = scanner.nextInt();
if (number == -1)
break;
if (number < lowest2 && number < lowest) {
lowest = number;
} else if (number < lowest2) {
lowest2 = number;
}
}
System.out.println("lowest:" + lowest);
System.out.println("lowest2:" + lowest2);
scanner.close();
}
}

How to check if a Float variable is negative in java

i am using the following code:
//Calculating Profit and Loss
float difference= sell_amount-buy_amount;
if (flag == 0) {
if ((difference<0)) {
System.out.print("Loss ");
System.out.println(difference - total_extra);
} else {
System.out.println("Profit ");
System.out.println(difference - total_extra);
}
}
even if in some inputs, the output is -0.53, it still says profit.. where am i going wrong

When you print out the difference, you also remove the value of total_extra.
Thus, let's say diffrence = 0.47 and total_extra = 1. The difference is indeed positive (thus printing "Profit", but when you print the value difference - total_extra, you print out "-0.53"