CODEWITHSUNDEEP
java
Zip
Zip

Reputation: 5592

Two dimensional ArrayList error

I am here trying to get an element from my two dimensional ArrayList but getting IndexOutOfBoundException error. What am I doing wrong here? Do I need to allocate the space like in a simple Array first? If so, How can I do it in two dimensional array? Below is the code,

import java.util.ArrayList;

public class Test {
    private ArrayList<ArrayList<String>> array;

    public Test(){
        array = new ArrayList<ArrayList<String>>();
        array.get(0).set(0, "00");
        array.get(0).set(1, "01");
        array.get(0).set(2, "02");
        array.get(1).set(0, "10");
        array.get(1).set(1, "11");
        array.get(1).set(2, "12");
        array.get(2).set(0, "20");
        array.get(2).set(1, "21");
        array.get(2).set(2, "22");
    }

    public String getE(int a, int b){
        return array.get(a).get(b);
    }

    public static void main(String[] args) {
        Test object = new Test();
        System.out.println(object.getE(0, 0)); // This gives me the error.
    }
}

Upvotes: 1

Views: 224

Answers (1)

fvrghl
fvrghl

Reputation: 3728

You need to initialize the ArrayLists before you insert into them. Like this:

public Test(){
    array = new ArrayList<ArrayList<String>>();
    array.add(new ArrayList<String>());
    array.add(new ArrayList<String>());
    array.add(new ArrayList<String>());
    array.get(0).add("00");
    array.get(0).add("01");
    array.get(0).add("02");
    array.get(1).add("10");
    array.get(1).add("11");
    array.get(1).add("12");
    array.get(2).add("20");
    array.get(2).add("21");
    array.get(2).add("22");
}

Right now, array is empty, so calling array.get(0) will result in the IndexOutOfBoundException. Once you add an initialized ArrayList at index 0, you will no longer get that error.

The constructor ArrayList<ArrayList<String>>() makes an empty ArrayList<ArrayList<String>>. It does not initialize the contents of array; you need to do that yourself.

Additionally, using set(int i , E e) gives you the same problem if there is not already an element at index i. You should use add(E e) instead. You can read more about set() at http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#set(int, E).

Upvotes: 3

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