get an error though proper initialized arraylist in java

Question

i want to passing value in arraylist, and initialized well. but there is an error -

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 3, Size: 0

I am trying hard, here is my code -


      public static void main(String[]args)
        {
            int n = 3;
            ArrayList<ArrayList<Integer>> graph = new ArrayList<>(n+2);
            for(int i=0; i < n+2 ; i++) {
                graph.add(new ArrayList<>(n+2));
            }
            graph.get(1).add(3,9);
            graph.get(2).add(3,1);
            graph.get(1).add(2,5);

            int s = 1, d = 3;
            System.out.println(dijkstra(s,d,graph));
        }

William Rosenbloom · Accepted Answer · 2020-05-22 14:23:54Z

2

You initialize your ArrayLists with capacity = n + 2, but the ArrayLists are still empty when they are first created. The capacity is different than the size.

capacity: The number of elements that could be added to the ArrayList without allocating any additional memory
size: The number of elements actually stored in the ArrayList

Your calls to ArrayList::add are throwing an out of bounds exception because an empty ArrayList cannot insert a value at index = 3. By definition, the first value that is added to any ArrayList will have index = 0.

Why are you trying to insert values at particular indices? The solution will depend on why you are doing that.

EDIT: SOLUTION

When you create the ArrayList, initialize it with n + 2 entries all with value = 0.

...
ArrayList<ArrayList<Integer>> graph = new ArrayList<>(n+2);
for(int i=0; i < n+2 ; i++) {
    ArrayList<Integer> sublist = new ArrayList<>(n+2);
    for (int j = 0; j < n + 2; j++) {
        sublist.add(0);
    }
    graph.add(sublist);
}
...

Keep the rest the same and it will behave as desired.

edited May 22, 2020 at 14:23

answered May 22, 2020 at 14:11

William Rosenbloom

2,6763 gold badges17 silver badges43 bronze badges

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

2 Comments

Dip Chakraborty Over a year ago

i want to pass graph's vertices, edges and value

William Rosenbloom Over a year ago

@DipChakraborty see my added solution

halfer · Accepted Answer · 2022-09-23 18:28:50Z

1

Problem

The following line means adding 9 at index, 3

graph.get(1).add(3,9);

However, graph.get(1) returns an ArrayList<Integer> which is empty. That's why you are getting the following error:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 3, Size: 0

Solution

Replace

graph.get(1).add(3,9);

with

graph.get(1).add(9);

which will add the element (e.g. 9 in this case) after the last index where an element has been added. In this case, 9 will be added at index, 0.

Update

Alternatively, you can initialize the inner list as follows:

for(int i=0; i < n+2 ; i++) {
    List<Integer> list = new ArrayList<>();
    for(int j = 0; j< n+2; j++){
        list.add(0);
    }
    graph.add(list);
}

and then you can carry on as follows (the way you have already done):

graph.get(1).add(3,9);
graph.get(2).add(3,1);
graph.get(1).add(2,5);

Update 2

Given below is the concise way based on Andy Turner's comment:

for (int i = 0; i < n + 2; i++) {
    graph.add(new ArrayList<>(Collections.nCopies(n + 2, 0)));
}

edited Sep 23, 2022 at 18:28

halfer

20.2k20 gold badges111 silver badges208 bronze badges

answered May 22, 2020 at 14:10

Arvind Kumar Avinash

81.1k10 gold badges98 silver badges144 bronze badges

6 Comments

Dip Chakraborty Over a year ago

i have to take two index

Arvind Kumar Avinash Over a year ago

@DipChakraborty - in that case, you need to initialize the inner list with some values.

Dip Chakraborty Over a year ago

can you help how to do?

Arvind Kumar Avinash Over a year ago

@DipChakraborty - I've updated my answer to fulfil this requirement. Feel free to comment in case of any doubt/issue.

Andy Turner Over a year ago

new ArrayList<>(Collections.nCopies(n+2, 0)) is a more concise way to "Alternatively, you can initialize".

|

Collectives™ on Stack Overflow

get an error though proper initialized arraylist in java

2 Answers 2

2 Comments

Problem

Solution

Update

Update 2

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Problem

Solution

Update

Update 2

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related