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Never ending for loop with user input

I am new to java and have just learned how to use user input. I have a for loop that goes through 10 times with user input to ask for a number. If the number is invalid, it should print "Invalid number" and not count towards the increasing for loop. Instead, it just loops forever saying 'Invalid number'.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int sum = 0;
Scanner scanner = new Scanner(System.in);
for(int i = 1; i<=10; i++){
System.out.println("Enter number #" + i + " ");
boolean validInt = scanner.hasNextInt();
if(validInt){
int num = scanner.nextInt();
sum += num;
} else{
System.out.println("Invalid Number");
i--;
}
}
System.out.println("Sum was " + sum);
scanner.close();
}
}

The problem is you are updating the iterator i at 2 places.
The better way is to update it according to the condition.
I would also suggest you to make use of wrapper classes for safe integer conversions and handle the exceptions properly like done in the following code:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int sum = 0;
Scanner scanner = new Scanner(System.in);
for(int i = 1; i<=10; ){
System.out.println("Enter number #" + i + " ");
String input = scanner.nextLine();
try{
int num = Integer.parseInt(input);
sum += num;
i++; // If input is a valid integer, then only update i
}catch(NumberFormatException e){
System.out.println("Invalid Number");
}
}
System.out.println("Sum was " + sum);
scanner.close();
}
}

I think you also can tweak the code using hasNextInt() directly in the while loop.
while (scanner.hasNextInt()) {
int num = scanner.nextInt();
sum += num;
}

I needed to add a
scanner.nextLine();
After the if and else statement to clear the scanner in both situations.

Program crashes when trying to catch exception

I'm trying to make a method that gets the user's input of 6 numbers and add them to a Tree set of integers. I'm trying to make a try and catch exception so if the users accidentally enters in a letter it'll catch the exception and ask them to enter in a number. Right now the program crashes when you try to enter in a letter. It'll print out "Invalid" then crashes. I'm not sure whats going on. Can anyone provide some insight?
public static Set<Integer> getTicket()
{
int userInput;
TreeSet<Integer> getNumbers = new TreeSet<Integer>();
Scanner input = new Scanner(System.in);
System.out.println("Enter your 6 numbers between 1-40: ");
for (int i = 0; i<6 ; i++)
{
try
{
System.out.print(i+1 + ": ");
userInput = input.nextInt();
}
catch (InputMismatchException e)
{
System.out.println("Invalid");
userInput = input.nextInt();
}
getNumbers.add(userInput);
}
System.out.println("Your ticket was: " + getNumbers);
return getNumbers;
}

Just a few notes on some of the changes made. From your original code, one thing I noticed that is not really an error but a head scratcher. Both of your methods (getWinning Numbers() and getTicket() ) returned a Set<integer> set, however you did not use it in main. So I simply took the output from the methods and placed them in the main method, where they should be IMHO. Methods like these should do ONE thing and in this case is return a set of integers. No printing or anything else that’s all it does.
I changed the logic in the getTicket() method. I simply set up a loop that continued until you had 6 valid numbers. Inside that loop I use a try statement to weed out the invalid input. The way the try statement is set up is one of many ways that you could accomplish this. As you can see the statement immediately after the try (guess = Integer.parseInt(userInput);) is where the invalid input problem could pop up and throw a NumberFormatException. If the input is invalid, you drop immediately to the catch where we output a message and continue. If the input is valid then we simply check for duplicates and the range of the number. If the numbers are ok then add it to pickedNumbers and increment numberCount.
public class Lottery
{
public static Set<Integer> generateWinningNumbers()
{
Random rndNumbers = new Random();
TreeSet<Integer> winningNumbers = new TreeSet<Integer>();
int max = 40;
int min = 1;
int range;
int sixNum;
for (int i = 0; i < 6; i++)
{
range = max - min + 1;
sixNum = rndNumbers.nextInt(range) + min;
while (winningNumbers.contains(sixNum))
{
sixNum = rndNumbers.nextInt(range) + min;
}
winningNumbers.add(sixNum);
}
return winningNumbers;
}
public static Set<Integer> getTicket(Scanner input)
{
String userInput;
int guess;
TreeSet<Integer> pickedNumbers = new TreeSet<Integer>();
System.out.println("Enter your 6 numbers between 1-40: ");
int numberCount = 1;
while(numberCount < 7)
{
System.out.print(numberCount + ": ");
userInput = input.nextLine();
try
{
guess = Integer.parseInt(userInput);
if( guess > 0 && guess < 41 && (!pickedNumbers.contains(guess)) )
{
pickedNumbers.add(guess);
numberCount++;
}
else
{
if (pickedNumbers.contains(guess))
{
System.out.println("Number already picked: " + guess);
}
else
{
System.out.println("Invalid number. Pick a number between 1-40: " + guess);
}
}
}
catch (NumberFormatException e)
{
// bad input
System.out.println("Invalid input: " + userInput);
}
}
return pickedNumbers;
}
}
Changes in the Main now take advantage of the methods returning a Set of integers for us. We create two Set<Integer> variables (winningTicket and userTicket) then we simply get the returned sets from the methods and output the results as opposed to printing the results from the methods.
public static void main(String[] args) throws IOException
{
Scanner userInput = new Scanner(System.in);
boolean done = false;
String yesNo;
Set<Integer> winningTicket;
Set<Integer> userTicket;
while(!done)
{
winningTicket = Lottery.generateWinningNumbers();
userTicket = Lottery.getTicket(userInput);
System.out.println("Your ticket was: " + userTicket);
System.out.println("Winning Numbers: " + winningTicket);
System.out.print("\nWould you like to try again? ");
yesNo = userInput.nextLine();
if(!yesNo.equalsIgnoreCase("y"))
{
System.out.println("Done");
done = true;
}
}
userInput.close();
}
Hope this helps

This happens because you don't catch exceptions inside cath block. for loop doesn't look good here, try while:
public static Set<Integer> getTicket()
{
int userInput;
TreeSet<Integer> getNumbers = new TreeSet<Integer>();
Scanner input = new Scanner(System.in);
System.out.println("Enter your 6 numbers between 1-40: ");
int correct = 0;
while(correct < 6)
{
try
{
System.out.print((correct+1) + ": ");
userInput = input.nextInt();
getNumbers.add(userInput);
correct++;
}
catch (InputMismatchException e)
{
System.out.println("Invalid input");
}
}
System.out.println("Your ticket was: " + getNumbers);
return getNumbers;
}
Also you cant't print collection that simple:
System.out.println("Your ticket was: " + getNumbers);
What you can do, is to use streams:
System.out.println("Your ticket was: " + getNumbers.stream().map(Object::toString).collect(Collectors.joining(" ")));

Java program will not recognize sentinel value

My program accept input data from a user (up to 20 values) and calculate the average/find the distance from the average. If the user enters "9999" when no numbers have been added yet it will display an error message and tell the user to re-enter a value. Otherwise entering "9999" will collect what the user has entered and do its calculations. My program will have to collect all 20 inputs from the user and also ignore when the value "9999" is entered completely but, it will do the other calculations correctly. I'm not sure why its not recognizing my sentinel value whatsoever.
package labpack;
import java.util.Scanner;
public class Lab4 {
public static void main(String[] args) {
int i = 0;
double [] numbers = new double[20];
double sum = 0;
int sentValue = 9999;
java.util.Scanner input = new java.util.Scanner(System.in);
System.out.print("Enter the numbers you want up to 20");
do {
for (i = 0; i < numbers.length; i++) {
if (numbers[0] == sentValue){
System.out.println("Error: Please enter a number");
break;
}
else {
numbers[i] = input.nextDouble();
sum += numbers[i];
}
}
while (i<numbers.length && numbers[i]!=sentValue); //part of do-while loop
//calculate average and distance from average
double average = (sum / i);
System.out.println("This is your average:" + average);
for (i = 0; i < numbers.length; i++) { //Display for loop
double diffrence = (average-numbers[i]);
System.out.println("This is how far number " +numbers[i] +" is from the average:" + diffrence);
}
}
}

You can do this without doing the do-while and doing while instead.
if (numbers[0]== sentValue){
System.out.println("Error: Please enter a number");
break;
Here you are trying to compare the value without initializing the array with the user input.
This can be done in a much simple way :
import java.util.Scanner;
public class Lab4 {
public static void main(String[] args) {
int i = 0;
double [] numbers =new double[10];
double sum =0;
double sentValue=9999;
int count = 0;
System.out.println(numbers.length);
System.out.print("Enter the numbers you want up to 20");
Scanner input = new Scanner(System.in);
while (i<numbers.length){
double temp = input.nextDouble();
if (temp >= sentValue){
if(i==0){
System.out.println("Error Message Here");
} else {
break;
}
}//if
else {
numbers[i] = temp;
sum += numbers[i];
i++;
count++;
}
} //part of while loop*/
//calculate average and distance from average
double average=(sum/i);
System.out.println("This is your average:" + average);
for (i=0;i < count;i++){ //Display for loop
double diffrence = (average-numbers[i]);
System.out.println("This is how far number " +numbers[i] +" is from the average:" + diffrence);
}//for loop
}//main bracket
}//class lab4 bracket
You need to store the value of the input.nextDouble() into a variable because when the compiler reads input.nextDouble(), each time it will ask the user for an input.
PS. You dont need to re-initialize this part :
java.util.Scanner input = new java.util.Scanner(System.in);
The above line can simply be written as :
Scanner input = new Scanner(System.in);
because you already imported Scanner.
import java.util.Scanner;
Hope this helps :)

Counting occurrences of integers in an array program java

I am trying to find the occurrences of all integers submitted by the user into the program and so far here's what I got. It works but I don't think it's a legit way to do it, is there any way I can try to do this without using the list[10]=9999;? Because if I don't do it, it'll show out of boundary error.
import java.util.*;
public class OccurrencesCount
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
int[] list = new int[11];
//Accepting input.
System.out.print("Enter 10 integers between 1 and 100: ");
for(int i = 0;i<10;i++){
list[i] = scan.nextInt();
list[10] = 9999;
}
//Sort out the array.
Arrays.sort(list);
int count = 1;
for(int i = 1;i<11;i++){
if(list[i-1]==list[i]){
count++;
}
else{
if(count<=1){
System.out.println(list[i-1] + " occurs 1 time.");
}
else{
System.out.println(list[i-1] + " occurrs " + count + " times.");
count = 1;
}
}
}
}
}

Personally, I think this is a perfectly good solution. It means that you can deal with the last group in the same way as all others. The only change I would make is putting the line list[10] = 9999; outside the for loop (there's no reason to do it 10 times).
However, if you want to use an array of length 10, you can change the line
if(list[i-1]==list[i])
to
if(i < 10 && list[i-1]==list[i])
If you do this, you won't get an ArrayIndexOutOfBoundsException from list[i] because the expression after the && is not evaluated when i == 10.

import java.util.*;
class OccurrencesCount {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int[] list = new int[101];
System.out.print("Enter 10 integers between 1 and 100: ");
for(int i = 0;i<10;i++) {
int x = scan.nextInt();
list[x]++;
}
for(int i = 1; i <= 100; i++)
if(list[i] != 0)
System.out.println(i + " occurs " + list[i] + " times ");
}
}
To store count of numbers from 1 to 100 you need to use a list of 100 integers each one storing the number of occurrences of itself. Better approach would be to use a Map.

I have made use of ArrayList and Collections package instead of regular arrays as a different flavor if it interests you check it out.
import java.util.*;
public class OccurrencesCount {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
List<Integer> list = new ArrayList<>();
//Accepting input.
System.out.print("Enter 10 integers between 1 and 100: ");
for (int i = 0; i < 10; i++) {
list.add(scan.nextInt());
}
Collections.sort(list);
Integer prevNumber = null;
for (int number : list) {
if (prevNumber == null || prevNumber != number) {
int count = Collections.frequency(list, number);
System.out.println(number + " occurs " + count + (count > 1 ? " times." : " time."));
}
prevNumber = number;
}
}
}

I got it figured out guys, only changed a couple of small things inside the conditions and everything went smoothly! Thanks for the help! Now I just need to find a way to restrict the inputs from going above 100.
import java.util.*;
public class CountOccurrences
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
int[] list = new int[10];
//Accepting input.
System.out.print("Enter 10 integers between 1 and 100: ");
for(int i = 0;i<=9;i++){
list[i] = scan.nextInt();
}
//Sort out the array.
Arrays.sort(list);
int count = 1;
for(int i = 1;i<=10;i++){
if(i<=9 && list[i-1]==list[i]){
count++;
}
else{
if(count<=1){
System.out.println(list[i-1] + " occurs 1 time.");
}
else{
System.out.println(list[i-1] + " occurrs " + count + " times.");
count = 1;
}
}
}
}
}

need character to print in output lines

I need these lines to output when a letter is typed instead of a whole number. I am not sure how to get it to do this: I have the code and what I need posted below if you can help me solve this issue, thank you.
This is what I am getting:
Input a valid whole number: abc
Input is not a valid number
Press any key to continue . . .
This is what I need:
Input a valid whole number: **ABC**
**ABC** is not a valid number
Press any key to continue . . .
below is what i have so far:
import java.io.PrintStream;
import java.util.Scanner;
public class FinalPractice
{
public static void main(String [] args)
{
Scanner scanner = new Scanner( System.in );
PrintStream out = System.out;
out.print( "Input a valid whole number: " );
String input = scanner.next();
int number;
try {
number = Integer.parseInt(input);
} catch (Exception e) {
out.println("Input is not a valid number");
return;
}
if (number < 0) {
out.println(number + " is not a valid number");
return;
}
printDivisors(number);
}
private static void printDivisors(int x){
PrintStream out = System.out;
for (int i=1; i<x; i++) {
if (isDivisibleBy(x, i)){
out.println(x + " is divisible by " + i);
} else {
out.println(x + " is not divisible by " + i);
}
}
}
private static Boolean isDivisibleBy(int x, int divisor){
while (x > 0) {
x -= divisor;
if (x == 0){
return true;
}
}
return false;
}
}

If I'm understanding correctly, you want your error message to include what the user actually inputted.
Change
out.println("Input is not a valid number");
to
out.println (input + " is not a valid number");
This takes your variable input, merges it with the rest of the String and it will then be displayed to the output console.