How to convert from an ArrayList of arrays to an array of arrays

Question

//edit: I changed my ArrayList conversion, but I am unable to load the second spinner

What am I doing wrong. I would like to fill a second spinner with an array of w depending on the row selected in the first spinner, but am getting this warning when trying to convert from array list.

***I have this marked in code Null Pointer Exception 11-06 19:03:34.050: WARN/System.err(5342): at RetrievingAmazonXMLDataActivity.onCreate(RetrievingAmazonXMLDataActivity.java:88)

// edited code

for (int i = 0; i < tokens.length; i++) {
            String a = dumpTitles("ProductName", i);
            element = a.split("!");
            allProducts.add(element);
        }

       w =  (String[][])allProducts.toArray(new String[allProducts.size()][]);


Spinner spinnerProducts = (Spinner) findViewById(R.id.spinner2);
        spinnerProducts.setOnItemSelectedListener(this);

// ** error line below

 ArrayAdapter<String> productsArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, productArrayToShow);

       productsArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinnerProducts.setAdapter(productsArrayAdapter);

 public void onItemSelected(AdapterView<?> parent, View v, int position, long id)
    {

        try {
            selected = parent.getItemAtPosition(position).toString();


            productArrayToShow = w[position];

        } catch (Exception e) {}
    }

// original code

ArrayList<String[]>allProducts = new ArrayList<String[]>();
    for (int i = 0; i < tokens.length; i++) {
        String a = dumpTitles("ProductName", i);
        element = a.split("!");
        allProducts.add(element);
    }


    String[][] w; = new String[allProducts.size()][];
        for (int a = 0; a<allProducts.size(); a++) {
            w[a] = (String[])allProducts.toArray(new String[allProducts.size()]);
        }

Once a question has been answered, don't change it into a question about the next problem you run into. Post a new question. — Laurence Gonsalves
– Laurence Gonsalves, Commented Nov 7, 2011 at 1:25

sjr · Accepted Answer · 2011-11-07 00:51:31Z

9

Why not just

String[][] w = allProducts.toArray(new String[][] {});

answered Nov 7, 2011 at 0:51

sjr

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Comments

Laurence Gonsalves · Accepted Answer · 2017-10-30 21:07:03Z

6

It looks like you changed your mind about how you were going to do the conversion half way through. Your code is a bit of this:

String[][] w = new String[allProducts.size()][];
for (int a = 0; a<allProducts.size(); a++) {
  w[a] = allProducts.get(a);
}

and a bit of that:

String[][] w = allProducts.toArray(new String[allProducts.size()][]);

Either will work, though the latter is shorter, and possibly more efficient.

edited Oct 30, 2017 at 21:07

answered Nov 7, 2011 at 0:54

Laurence Gonsalves

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2 Comments

tom Over a year ago

The (String[][]) casting is redundant. You don't need that.

Laurence Gonsalves Over a year ago

@tom You are correct. I have updated the answer. Thanks!

Ted Hopp · Accepted Answer · 2011-11-07 00:51:49Z

1

I think you can get by with just this:

String[][] w = allProducts.toArray(new String[allProducts.size()]);

answered Nov 7, 2011 at 0:51

Ted Hopp

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Comments

codepreneur · Accepted Answer · 2011-11-07 00:51:10Z

0

Make them of the same datatype an "ArrayList" and a "Array of Strings" they are not of the same datatype, so they wont be compartable with each other. And please comment where the problem is.

answered Nov 7, 2011 at 0:51

codepreneur

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9 Comments

codepreneur Over a year ago

like i have sad try to make sure you convert them to the same data types. For instance w[a] = Convert.ToString(allProducts[a])

Dave Newton Over a year ago

Right, and that was the question--answering the "how do I convert these" with "you need to convert them" isn't that useful, that's all I'm saying.

codepreneur Over a year ago

it is very very usefull buddy. you have to convert them to the same type. if it is from ArrayList to String[] make sure the values are converted to Strings.

Dave Newton Over a year ago

... I'll try one more time. The original question was "how do I convert?" The answer isn't "you need to convert", the poster is already trying to convert, and was asking how. There's no conversion to strings involved, the issue is converting from List<String[]> to String[][]. They're asking how.

codepreneur Over a year ago

b patient with me Dave.try this code and see if it is not converting like i was saying. List<string> allProducts = new List<string>(); allProducts.Add("12"); String[] w = new String[1]; w[0] = allProducts[0]; Console.WriteLine(allProducts[0]); Console.ReadKey();

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