Java error with "exception in thread"

Question

Hey guys I'm currently making a program where it will reverse the input from the user. Currently my code is

import java.util.*;

public class Reverse {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        List<String> input = new ArrayList<>();
        while (in.hasNextLine())
            input.add(in.nextLine());
        for (int x = 0; input.size() >= x; x++) {
            String reverse = "";
            for (int z = input.get(x).length(); z > 0; z--) {
                reverse += input.get(x).charAt(z - 1);
            }

            System.out.println(reverse);
        }
    }
}

But I'm getting the error where it says

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
at java.util.ArrayList.rangeCheck(ArrayList.java:653)
at java.util.ArrayList.get(ArrayList.java:429)
at Reverse.main(Reverse.java:12)*

Any help would be greatly appreciated thanks!

You need to read about length and size of the array. Index of array starts from 0; So when you have 3 elements, they will be indexed 0,1,2; At the same time the size of the array is 3; You error is due to the equalOrGreater comparison. I will recommend reading about the foreach loop which will save you some trouble in the future! Good luck! — hovanessyan
– hovanessyan, Commented Apr 5, 2016 at 10:50

Tim Biegeleisen · Accepted Answer · 2016-04-05 10:45:40Z

2

Change the bounds of your for loop:

for (int x=0; x < input.size(); x++) {
    String reverse = "";
    for (int z=input.get(x).length(); z > 0; z--) {
        reverse += input.get(x).charAt(z - 1);
    }

    System.out.println(reverse);
}

Accessing a List is zero-based, so in your outer loop, for a list of size 3, the greatest value you want for the x index is 2.

answered Apr 5, 2016 at 10:45

Tim Biegeleisen

526k32 gold badges323 silver badges399 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Wakachopo · Accepted Answer · 2016-04-05 10:46:00Z

0

On last iteraton, "x" is equal to input.size(), so element input.get(x) will not exist, at the second "for" loop.

answered Apr 5, 2016 at 10:46

Wakachopo

1497 bronze badges

Comments

JB Nizet · Accepted Answer · 2016-04-05 10:48:17Z

0

input.size() >= x

At the last iteration, x is equal to the size of the list. Since list indices start at 0, this is an invalid index.

The idiomatic way of looping by index in Java is

for (int x = 0; x < size; x++)

You should use this idiomatic way.

But for such a loop, where you don't need the index, you should use a for-each loop:

for (String s : input) {

This way is safer, guaranteed to be efficient whatever the type of the list is, and is more readable too.

answered Apr 5, 2016 at 10:48

JB Nizet

694k94 gold badges1.3k silver badges1.3k bronze badges

Comments

VALARMATHI · Accepted Answer · 2016-04-06 06:13:54Z

0

    package com.stackwork;

    import java.util.*;

    public class Reverse {
        public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            List<String> input = new ArrayList<String>();
            while (in.hasNextLine())
                input.add(in.nextLine());
// prints the size of array
            System.out.println("the array size :" + input.size());
            for (int x = 0; input.size() > x; x++) {
//Prints the incremented x value at each step 
                System.out.println("the x value inside the for loop :" + x);
                String reverse = "";
                for (int z = input.get(x).length(); z > 0; z--) {
//prints the length of each string in the array
                    System.out.println("the value of z is :" + z);
                    reverse += input.get(x).charAt(z - 1);
//prints the value in each step of reverse
                    System.out.println("each step of reverse " + reverse);
                }

                System.out.println(reverse);
            }
        }
    }

edited Apr 6, 2016 at 6:13

answered Apr 5, 2016 at 11:40

VALARMATHI

414 bronze badges

1 Comment

CubeJockey Over a year ago

Comments and an explanation would make it even clearer! :)

Collectives™ on Stack Overflow

Java error with "exception in thread"

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related