Accessing object's elements of Multiple ArrayList in java

Question

I cannot access Multiple ArrayList element. The code is given below and it cannot access the values 5 or 6. My IDE is not accepting the last statement of my code which is System.out.println(specification.get(0).get(0).value); How can I get the elements of an Object in ArrayList which is within an array list.

class Node {

    int value;
    boolean explored;

    Node(int v) {
        value = v;
        explored = false;
    }

    int getValue() {
        return value;
    }
}

class Board {

    ArrayList<ArrayList> specification;
    ArrayList<Node> speci_node;

    Board() {
        speci_node = new ArrayList<Node>(1);
        speci_node.add(new Node(5));
        speci_node.add(new Node(6));

        specification = new ArrayList<ArrayList>(1);
        specification.add(speci_node);
        System.out.print(specification.get(0).get(0).value);  // variable 'value' is not found error....
    }
}

the IDE is not accepting the last statement. It is say variable 'value' is not found — Ayaz Khan
– Ayaz Khan, Commented Mar 4, 2017 at 20:01
Are both classes are in the same file? Or are they in different files and maybe different packages as well? — dpr
– dpr, Commented Mar 4, 2017 at 20:06

dpr · Accepted Answer · 2017-03-04 20:11:38Z

3

While @YCF_L's answer is correct, you could as well specify the generic type of the inner ArrayList to avoid the cast:

specification = new ArrayList<ArrayList<Node>>(1);

Furthermore the Node and Board classes need to be in the same package, as the value member is package private and thus not accessible outside of the package of the Node class. But this already seems to be the case here...

answered Mar 4, 2017 at 20:11

dpr

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Comments

Youcef LAIDANI · Accepted Answer · 2017-03-04 20:06:18Z

1

You should to cast your element like this :

System.out.print(( (Node) specification.get(0).get(0)).value);
//-----------------|-^^^-|-----------------------------------

This will return 5

answered Mar 4, 2017 at 20:06

Youcef LAIDANI

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6 Comments

fps Over a year ago

There's no need to cast if you declare the generic type correctly

Youcef LAIDANI Over a year ago

it still a solution @FedericoPeraltaSchaffner my answer help the OP so why this down-vote?

Youcef LAIDANI Over a year ago

mmmm @FedericoPeraltaSchaffner ok :)

fps Over a year ago

Because of what I stated in my previous comment: there's no need to cast if the outer ArrayList is correctly declared. If you edit your question and clarify this point, I will gladly undo my downvote

Youcef LAIDANI Over a year ago

My answer help the OP and it still a way to solve this problem, maybe the OP need it like this there are many solutions @FedericoPeraltaSchaffner ok you are free to make down-votes, i don't mind

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