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Working on a Java Program that utilizes For Loops to separate Even, Odd, and Negative Inputted Integers. Try Catch Handler Gives Out-of-bounds Error? [duplicate]

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What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?
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Closed 12 months ago.
I am working on a Java program that determines Evens, Odds, and Negative numbers from 12 inputted integers.
It then separates them into different arrays. The course I am following suggests building an exception handler and I utilized the Try-Catch Method for the Exception error I may receive.
It then creates an Out of Bounds error for counting these numbers when I enter a String.
I've commented on the area in which I have trouble reprompting the user. So far, I've tried prompting at the error with twelveInt [i] = in.nextInt(); and just in.next();.
Why is the program affected outside of the loop?
Here is the program:
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int [] twelveInt = new int [12];
int countEven = 0;
int countOdd = 0;
int countNeg = 0;
boolean ehandle = true;
for (int i = 0; i < twelveInt.length; i++) {
while(ehandle){
try{
System.out.println("Enter the #" + (i + 1) + " integer.");
twelveInt [i] = in.nextInt();
ehandle = false;
}
catch(Exception e){
System.out.println("Please enter integers only");
// Unsure of what to add here to handle the errors and allow me to reprompt. in.next();
//does not work nor does twelveInt [i] = in.nextInt();
}
if (twelveInt[i] % 2 == 0){
countEven++;
}
if (twelveInt[i] % 2 != 0){
countOdd++;
}
if (twelveInt[i] < 0){
countNeg++;
}
}
}
int [] evens = new int [countEven];
int [] odds = new int [countOdd];
int [] negatives = new int [countNeg];
countEven = 0;
countOdd = 0;
countNeg = 0;
for (int i : twelveInt) {
if (i % 2 == 0){
evens[countEven++] = i;
}
if (i % 2 != 0){
odds[countOdd++] = i;
}
if (i < 0){
negatives[countNeg++] = i;
}
}
System.out.println("Here are the Even numbers you entered");
System.out.println(Arrays.toString(evens));
System.out.println("Here are the Odd numbers you entered");
System.out.println(Arrays.toString(odds));
System.out.println("Here are the Negative numbers you entered");
System.out.println(Arrays.toString(negatives));

The problem in your code is that after you run your loop and enter your first number, you then define ehandle = false.
This means that you never enter the rest of your loop since you exit the while loop. Therefore, you never increment the values of countEven, countOdd, or countNeg.
This results in an error because when you try running this line: int [] evens = new int [countEven]; , countEven is still 0, so you get an error when you try to iterate it.
To avoid this error, you can modify your try catch error as so:
import java.util.*;
import java.io.*;
class Main {
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int [] twelveInt = new int [12];
int countEven = 0;
int countOdd = 0;
int countNeg = 0;
for (int i = 0; i < twelveInt.length; i++) {
System.out.println("Enter the #" + (i + 1) + " integer.");
boolean error = true;
while (error) {
try {
twelveInt [i] = in.nextInt();
if (twelveInt[i] % 2 == 0){
countEven++;
}
if (twelveInt[i] % 2 != 0){
countOdd++;
}
if (twelveInt[i] < 0){
countNeg++;
}
error = false;
}
catch (Exception e) {
System.out.println("Please enter integers only");
in.next();
}
}
}
int [] evens = new int [countEven];
int [] odds = new int [countOdd];
int [] negatives = new int [countNeg];
countEven = 0;
countOdd = 0;
countNeg = 0;
for (int i : twelveInt) {
if (i % 2 == 0){
evens[countEven++] = i;
}
if (i % 2 != 0){
odds[countOdd++] = i;
}
if (i < 0){
negatives[countNeg++] = i;
}
}
System.out.println("Here are the Even numbers you entered");
System.out.println(Arrays.toString(evens));
System.out.println("Here are the Odd numbers you entered");
System.out.println(Arrays.toString(odds));
System.out.println("Here are the Negative numbers you entered");
System.out.println(Arrays.toString(negatives));
}
}
We first try taking in the user input, and if we get an exception error, we will use the catch so our code does not terminate. NOTE: we must do in.next() otherwise we will get an infinite loop (since integers leave a trailing newline, resulting in infinite exceptions).
I hope this helped! Please let me know if you need any further clarifications or details :)

If you want to reiterate your while(ehandle) loop when you get an exception, you can put continue in your catch block. But you should set ehandle back to true at the top of your for-loop.
for (int i = 0; i < twelveInt.length; i++) {
ehandle = true;
while (ehandle) {
try {
System.out.println("Enter the #" + (i + 1) + " integer.");
twelveInt[i] = in.nextInt();
ehandle = false;
} catch(Exception e) {
System.out.println("Please enter integers only");
continue;
}
...

After re-run program with while loop , exception method doesn't work

I'm handling exceptions for an exercise and runs fine until I enter an invalid number (to try) after running the program for the first time, this is after the first run when asking to re-run with different values if I happen to enter invalid values it won't throw the exception and I don't know why? It's something I don't know or is it my code? Thanks
//program ReverseNumbers.java
//This program reverses the digits of each number in an array.
import java.util.Scanner;
public class ReverseNumbers{
public static void main(String[] args){
Scanner input = new Scanner(System.in);
int[] numbers = new int[5]; //create array numbers size 5
boolean continueInput = true; //controls loop for input
String another = "y";
while(another.equalsIgnoreCase("Y")){ //loop to re-run program
do{
System.out.print("\nEnter 5 positive integers: "); //prompt the user to enter 5 integers
//try block
try{
for(int i = 0; i < numbers.length ; i++) //initialize the array
numbers[i] = input.nextInt();
checkInput(numbers); //handler method
continueInput = false;
}
//catch block
catch(IllegalArgumentException ex){
System.out.print("\nInvalid input: ");
//input.nextLine();
}
}while(continueInput);
//outputs
System.out.print("\nEntered numbers:\t\t");
for(int e: numbers)
System.out.print(e + " ");
System.out.print("\nReversed numbers:\t\t");
reverse(numbers);
//output re-run program
System.out.println();
System.out.print("\nRe-run program with different values, Y/N? ");
another = input.next();
}
}
//Exception method
public static void checkInput(int[] array) throws IllegalArgumentException {
for(int i = 0; i < array.length; i++){
if(array[i]<0)
throw new IllegalArgumentException();
}
}
//method reverse.
public static void reverse(int[] array) {
//reverse order of element within the array
int i, k, t;
int n = array.length;
for (i = 0; i < n / 2; i++) {
t = array[i];
array[i] = array[n - i - 1];
array[n - i - 1] = t;
}
reverse(array, array.length-1);
}
//helper method
public static void reverse(int[] array, int n){ //reverse the order of the number for each element in the array
// n, number of elements in the array
if(n>=0){
int Element = array[n]; //element n in array
int NewElement = -1;
int Digit = -1;
String s = "";
if(Element<10)
s = Element + "";
while(Element >= 10){ //loop up to element is reduced to one digit number
Digit = Element%10;
s = s + "" + Digit; //save the digits
NewElement = Element/10;
if(NewElement < 10) //when NewElement has 1 digit left
s = s + "" + NewElement;
Element = NewElement;
}
System.out.print(s + " "); //print digit
reverse(array, n-1); //recursive call
}
}
}

This can be fixed simply by inserting continueInput = true in your outer while loop. Without that, continueInput will always be false after the first time you enter a valid input, and your do-while loop will always exit after one iteration.
However, I wouldn't suggest throwing exceptions yourself, and you should probably handle Scanner's InputMismatchException. Also, your reverse method is unnecessarily complicated. Here's the code I got:
import java.util.Scanner;
public class ReverseNumbers {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int[] numbers = new int[5]; //create array numbers size 5
String another = "y";
while (another.equalsIgnoreCase("Y")) { //loop to re-run program
boolean continueInput = true; //controls loop for input
outer: do {
System.out.print("\nEnter " + numbers.length + " positive integers: ");
try {
for (int i = 0; i < numbers.length; i++) {
int num = input.nextInt();
if (num < 0) {
System.out.print("Invalid input, found a negative integer " + num)
continue outer;
} else {
numbers[i] = num;
}
}
continueInput = false;
}
//handle bad inputs that aren't digits
catch (InputMismatchException ex) {
System.out.print("\nInvalid input, please enter integers");
}
} while (continueInput); //outputs
System.out.print("\nEntered numbers:\t\t");
for (int e: numbers) System.out.print(e + " ");
System.out.print("\nReversed numbers:\t\t");
for (int i = numbers.length - 1; i >= 0; i--) {
System.out.print(numbers[i] + (i == 0 ? "\n" : " "));
}
//output re-run program
System.out.println();
System.out.print("\nRe-run program with different values, Y/N? ");
another = input.next();
}
}
}

How am i going to use while loop and if else if user enter the same input twice and it will try again

I want to apply this function in java. Inside while loop, you need to input number of repetition you want to input a number. if you input a number that equals to the number that you enter previously, it will repeat a loop and enter a number again. This code is not finish yet. I hope u understand what i want to achive. thank you
System.out.print("Enter number of times: ");
int times = number.nextInt();
int i = 1;
while ( i <= times){
System.out.print("Enter a number : ");
int input = number.nextInt();
i++;
if( input == input){
System.out.println("It is already taken");
}
}
}
}

Let's use a temp variable to store the value of previous input. If new input is same as previous input, the iterator i should not increase, so we use i--
System.out.print("Enter number of times: ");
int times = number.nextInt();
int i = 1;
int temp=0;
int inputArray[] = new int[times];
while ( i <= times){
System.out.print("Enter a number : ");
int input = number.nextInt();
i++;
if( input == temp){
System.out.println("It is already taken");
i--;
}else {
inputArray[i-2]=input;
}
temp=input;
}
}

The thing with that solution is that is only checks for the number just entered before the current one. I understood that you want to check that the number the user entered is unique and it has to be checked against every number that he/she has entered before.
See the code for that:
import java.util.Scanner;
import java.util.ArrayList;
public class testMe{
public static void main(String[] args){
Scanner scanner = new Scanner(System.in);
System.out.print("Enter number of times: ");
int times = scanner.nextInt();
int i = 0;
ArrayList<Integer> listWithEntries = new ArrayList<Integer>();
while (i < times){
System.out.print("Enter a number : ");
int input = scanner.nextInt();
if(listWithEntries.size() == 0){
listWithEntries.add(input);
i++;
} else {
for(int j = 0; j < listWithEntries.size(); j++){
if(input == listWithEntries.get(j)){
System.out.println("It is already taken!");
break;
}
if(j == listWithEntries.size()-1 && input !=
listWithEntries.get(j)){
listWithEntries.add(input);
i++;
break;
}
}
}
}
}
}

Java try-catch statement inside while loop

I have this method and it works fine. I need to put a try/catch statement so
the method can continue if the user puts in a letter. I don't know where to put the statement, It seems everywhere I put it it get's wrong. Could somebody please show me where to put this statement?
public void myMethod() {
Scanner in = new Scanner(System.in);
int array[] = new int[21];
int number;
boolean end = false;
while (!end) {
System.out.println("Please give an number between 0-20: ");
number = in.nextInt();
for (int i = 1; i < array.length; i++) {
if (i == number) {
System.out.println(array[number]);
end = true;
}
}
if (!end) {
System.out.println("I cant find number " + number
+ " in the array, please try again ");
}
}
}

Your for loop I can't explain, you need only check values between 0 and 20,
And when you call try catch, you have to skip loop after exception
public static void myMethod() {
Scanner in = new Scanner(System.in);
int array[] = new int[21];
int number=0;
boolean end = false;
while (!end) {
System.out.println("Please give an number between 0-20: ");
//check symbol
try{
number = Integer.valueOf(in.next());
}catch(Exception e)
{
System.out.println("It's not a number! ");
continue; //skip loop
}
if((number>=0)&&(number<=20))
{
System.out.println(array[number]);
end=true;
}
else
System.out.println("I cant find number " + number
+ " in the array, please try again ");
/* why do you use loop here???
* u need to check if number between 0-20
for (int i = 1; i < array.length; i++) {
if (i == number) {
System.out.println(array[number]);
end = true;
}
}*/
}
}

public static void main(String[] args) {
Test test = new Test();
Scanner in = new Scanner(System.in);
int array[] = new int[21];
int number;
System.out.println("Please give an number between 0-20: ");
do{
try{
number = Integer.parseInt(in.next());
}
catch(Exception e){
System.out.println("Please give an number between 0-20: ");
number = -1;
}
}
while(!(number <= 20 && number >=0 ));
System.out.println(array[number]);
}

System.out.println("Please give an number between 0-20: ");
try{
number = in.nextInt();
}catch(Exception e){
number = 1; //Put random number of default number here
}

Input validation loop in java

How would I write an input validation loop and at least one other loop, either counter-controlled or sentinel-controlled. Could you help me how to write any type of code?

final int SIZE = 10;
int [] array = new int[SIZE];
Scanner input = new Scanner(System.in);
for(int i=0; i < array.length; i++)
{
try
{
do
{
System.out.print("Enter Number " + (i+1) + ": ");
array[i] = input.nextInt();
if(array[i] < 0)
System.out.println("Invalid Input - Must be Greater than 0");
}while(array[i] < 0);
}
catch (InputMismatchException e)
{
System.out.println("Invalid Input - Not an Int - Re-Enter");
input.nextLine();
i--;
}
}