Thread: [SOLVED] How to output a range of values from arraylist and user input

I assume -1 was counted as the last index when I stopped the loop from running. How can I exclude -1 from inputNumber (input user in this case) and stop the while loop at the same time?

Exception in thread "main" java.lang.IndexOutOfBoundsException: fromIndex = -1
at java.base/java.util.AbstractList.subListRangeCheck(AbstractL ist.java:505)
at java.base/java.util.ArrayList.subList(ArrayList.java:1138)
at OnlyTheseNumbers.main(OnlyTheseNumbers.java:27)

this is the error message I was refering to, do you mean it is located in line code 27?

Originally Posted by Norm

That says the error was at line 27 where the code calls the subList method.

You can see the contents of the list by printing it after the end of the loop that gets its contents.

Look at the API doc for the indexOf method to see what values it returns. Is -1 ever returned?

Thank you for clarifying that part, I did print out the content of that array list by simply adding system.out.println(listOfNumbers) which shows me the whole set of an array list, if i input 5 random numbers, it outputs [1,2,3,4,5]

what do I do in this case to only show a range of that array let's say from 1 to 3 or from 1 to 4? Do I remove the sublist and use another method?

And to answer your question, I do not think an index of -1 will ever be returned because indices start from 0 to infinity, not from -1

Originally Posted by Norm

Read the API doc for the indexOf method. It clearly says that a -1 can be returned.

Add some print statements that print out the values of all the variables the code uses so that you can see what the computer sees when the code is executed.

Note: You are mixing up the value of an index with the contents of the list at that index.
For example, an index of 1 finds a value of 20 in the list.

this turned out to be more confusing than I thought

Why can it return -1 and what is the point of that?

To clear my confusions,

.size gives the size of an array by totalling the amount of indices (not their content, it only counts how many indices are there)

.get retrieves the index number (not its content)

.indexOf what does it do? it says that: "Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that Objects.equals(o, get(i)), or -1 if there is no such index."

the definition of .indexOf is really confusing in netbeans and I really cannot get my head around it ;/

.subList is defined by 2 parameters 1 is inclusive and the other one is exclusive, what does that even mean too?

Originally Posted by Norm

inclusive means it includes that value
exclusive means it does not include that value
Given a list: ABCDE

ask for items including the first (index 0) through and excluding index 3 (D is @ index 3) would give ABC

Thank you for clarifying the concept, I have managed to pull the output as I wanted it to be. But, when I input any random numbers in an array list and try to input -1 to stop the loop, the while loop does not stop at all. Do you recommend me to ask a new question about that or do I continue in this topic? Because my problem is solved but not with the while loop break

Kindly, take a look at my modified code

 
 
import java.util.ArrayList;
import java.util.Scanner;
 
public class OnlyTheseNumbers 
{
 
    public static void main(String[] args) 
    {
        Scanner inputReader = new Scanner(System.in);
        ArrayList<Integer> listOfNumbers = new ArrayList<>();
 
 
        while (true) 
        {
            int inputNumber1 = Integer.valueOf(inputReader.nextLine());
            if (inputNumber1 == -1) 
            {
                break;
            } 
            listOfNumbers.add(inputNumber1);
        }
 
        int inputNumber2 = Integer.valueOf(inputReader.nextInt());
        System.out.println("From where? " + inputNumber2);
 
        int inputNumber3 = Integer.valueOf(inputReader.nextInt());
        System.out.println("To where? " + inputNumber3);
 
        System.out.println(listOfNumbers.subList(inputNumber2, inputNumber3 + 1));
 
    }
}

Originally Posted by Norm

It does for me. Can you run the program, copy the output window and paste it here so I can see?

10
20
30
40
50
-1
0
From where? 0
2
To where? 2
[10, 20, 30]

After i inputted -1 the console output was still running. After I have inputted 0 and then 2, it gave me the range of element values inside an array list and then the loop stopped

https://images2.imgbox.com/2b/ca/bZJq8q3N_o.png

Is there a possibility to make the loop stop after I input -1 and can input 2 values for the range?

Originally Posted by Norm

The code reads the 0 before it prints out the From where message.
The code to read the 0 is outside of the loop. Add a print statement after the loop that prints out the contents of the array.
That will show you that the loop has exited.

that is really strange: https://imgbox.com/9Wi67jLg

I have added system.out.println(listOfNumbers) to show the set or collection of array, the loop still did not break. why is the IF condition not working?

Originally Posted by Norm

Please copy the console's contents and paste it here. No images. Text can not be copied from an image to include in a response.


Please post the new code and the contents of the console from when the program executes.

 
import java.util.ArrayList;
import java.util.Scanner;
 
public class OnlyTheseNumbers 
{
 
    public static void main(String[] args) 
    {
        Scanner inputReader = new Scanner(System.in);
        ArrayList<Integer> listOfNumbers = new ArrayList<>();
 
 
        while (true) 
        {
            int inputNumber1 = Integer.valueOf(inputReader.nextLine());
            if (inputNumber1 == -1) 
            {
                break;
            } 
            listOfNumbers.add(inputNumber1);
        }
 
        System.out.println(listOfNumbers);
 
        int inputNumber2 = Integer.valueOf(inputReader.nextInt());
        System.out.println("From where? " + inputNumber2);
 
        int inputNumber3 = Integer.valueOf(inputReader.nextInt());
        System.out.println("To where? " + inputNumber3);
 
        System.out.println(listOfNumbers.subList(inputNumber2, inputNumber3 + 1));
 
    }
}

Console output

10
20
30
40
50
60
70
-1
[10, 20, 30, 40, 50, 60, 70]
0
From where? 0
3
To where? 3
[10, 20, 30, 40]

Originally Posted by Norm

I don't see where the problem is. The console output looks as expected.

What do you think the output should look like? Can you post what you expect to see?

the output should look exactly like this according to the exercise:

10
20
30
40
50
-1
From where? 0
To where? 2
[10, 20, 30]

as opposed to my current output

10
20
30
40
50
60
70
-1
[10, 20, 30, 40, 50, 60, 70]
0
From where? 0
3
To where? 3
[10, 20, 30, 40]

perhaps the problem is with re-initiating the inputNumber integer to the scanner 2 times (so the scanner can read again with a whole new scanning) but this is just an assumption

I do not think that this is possible because I still need to declare a new scanner input variable for 2 values and the declaration has to be done before printing it out. How can I print something that has not been declared before?

I have tried declaring both inputNumber2 and 3 before and outside the loop, inside the loop and after outside the loop, there was no result.

Originally Posted by Norm

Did you try it?
The code would like like this:
print the message
read user's response to the message

If you print the value that was read, it will appear on the console 2 times ( that is the current problem)
first time would be when entered
second time when printed

I have tried it numerous times. If a question is asked to the user, the user is able to respond to that question. But in Java, a variable must be declared before a question is asked. If there is a way to oppose what I have just said, then please prove it in coding because I really cannot think much about it and I will just leave it for now. I have spent the entire day trying to solve this entire exercise and time is against me.

Originally Posted by Norm

That is not true. A program can ask many questions without declaring any variables.
A variable must be declared before it is used.
Asking a question and using a variable do not need to be related.

Quite interesting, even though I struggled with a simple exercise, I did learn a lot.

I thank you for your insight and understanding.

I have finally solved the problem, would you like me to provide the solution as a reference to others or just keep it as it is from here?

Originally Posted by Norm

Glad you got it working.

A working solution might be helpful for others.

Thank you once again

 
import java.util.ArrayList;
import java.util.Scanner;
 
public class OnlyTheseNumbers {
 
    public static void main(String[] args) {
        Scanner inputReader = new Scanner(System.in);
        ArrayList<Integer> listOfNumbers = new ArrayList<>();
        int inputNumber1;
        int startIndex;
        int endIndex;
 
        while (true) {
            inputNumber1 = Integer.valueOf(inputReader.nextLine());
            if (inputNumber1 == -1) {
                break;
            }
            listOfNumbers.add(inputNumber1);
        }
 
        System.out.println("From where? ");
        startIndex = Integer.valueOf(inputReader.nextInt());
 
        System.out.println("To where? ");
        endIndex = Integer.valueOf(inputReader.nextInt());
 
        System.out.println(listOfNumbers.subList(startIndex, endIndex + 1));
    }
}