CODEWITHSUNDEEP
javaarraylist
user1174868
user1174868

Reputation:

Using a custom class with ArrayLists

Why is this wrong? I can't use add, I am not sure how to. Some java documentation says I need to have add(index,data) but others are just add(data) and the compiler is support that as well. It is having an error with my data type.

import java.util.*;
public class graph1 {

    public static void main (String[] args){
        ArrayList<Node> web = new ArrayList<Node>();    
        web.add(0, "google", new int[]{1,2});

    }
}

Node.java: 

 public class Node {
        int i;
        String title;
        int[] links;    

        Node(int i, String title, int[] links){
            this.i = i;
            this.title = title;
            this.links = links;
        }
    }

Upvotes: 2

Views: 2064

Answers (5)

Marko Gresak
Marko Gresak

Reputation: 8207

Your custom class has to be instantiated in order to add it to the ArrayList. To do this, use web.add(new Node(0, "google", new int[]{1,2}));.

In your case, you used web.add(0, "google", new int[]{1,2});, which java compiler understood as you were trying to add 3 object at once, thus compiler complained that something is wrong with your code.

Also, you should consider implementing (overriding) custom compare(o1, o2) if you'll need to sort the array, because the default Collections.sort(list) doesn't know how to correctly order your objects.

Upvotes: -1

drewdles
drewdles

Reputation: 244

You need to make the node like this

Node node = new Node(i, title, links);
web.add(node);

Upvotes: 2

Andrew_CS
Andrew_CS

Reputation: 2562

You have an arraylist of Nodes, but are trying to add a bunch of random variables. You need to use those variables to make a Node and then add that.

web.add(new Node(0, "google", new int[]{1,2}));

Upvotes: 1

C. K. Young
C. K. Young

Reputation: 223003

Use this:

web.add(new Node(0, "google", new int[] {1, 2}));

Upvotes: 2

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285403

You're forgetting to include new Node(...) inside of the ArrayList's add(...) method since you're not adding the combination of an int, a String and an array of int to the ArrayList, but rather you're adding a Node object. To do this, the Node object must be explicitly created and then added:

web.add(new Node(0, "google", new int[]{1,2}));

Upvotes: 4

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