ArrayList of ArrayLists

[coolnfunky_raj]

Hi all

I am new to Java. I am working with ArrayLists and have a couple of questions in that. So here goes..

#1. I have an ArrayList and I keep adding Strings to it. Upon a certain condition, I add this ArrayList to an ArrayList of ArrayLists like this

class Test
{
       ArrayList<String> arr = new ArrayList<String>();
       ArrayList<ArrayList> arrOfArr = new ArrayList<ArrayList>();
       
       public void startElement (String tagName)
       {
             arr.add(tagName);
       }
       public void endElement ()
       {
             arrOfArr.add(arr);
       }
       public void removeLastElement ()
       {
             arr.remove(arr.size() -1);
       }

       public static void main(String args[])
       {
             Test test = new Test();
             test.startElement("ABC");
             test.startElement("DEF");
             test.endElement();
             test.removeLastElement();
             test.removeLastElement();
       }
}

In this code, when removeLastElement() is executed, the elements in arr as well as arrOfArr are removed. Is there a way to remove elements from arr but leave arrOfArr intact?

#2. In the above code, is there a way to convert arrOfArr to a String[][] without iterating through arrOfArr element by element?

[coolnfunky_raj]

       public static void main(String args[])
       {
             Test test = new Test();
             test.startElement("ABC");
             test.startElement("DEF");
             test.endElement();
             test.removeLastElement();
             test.removeLastElement();
       }

I forgot to mention, I cant do arr = new ArrayList<String>(); after test.endElement(); as I want to further process this ArrayList and keep adding it to arrOfArr.

Thanks in advance


~

[Eranga]

In this code, when removeLastElement() is executed, the elements in arr as well as arrOfArr are removed. Is there a way to remove elements from arr but leave arrOfArr intact?

Refer the element with the index.

[srikanthkapila]

I am not sure what application you are trying to build. The code you have pasted here is not complete. Can you let us know in more detail what you require.

#2. In the above code, is there a way to convert arrOfArr to a String[][] without iterating through arrOfArr element by element?

From the second question it seems you are not a beginner at all.:)

[Eranga]

Srikanth, what you mean not complete. Any reason? I guess you are talking about packages. ;)

[coolnfunky_raj]

Refer the element with the index.

I am referring the element by index. I am finding the last element and removing it.

arr.remove(arr.size() -1);

[Eranga]

Likewise you have refer the required element. Do you want to check that element is another array list or just an element before remove it?

[srikanthkapila]

Not exactly. See the way the code has been implemented.

The elements have only been added and deleted in the first array. I was not sure what was the reason to use the second arraylist for the above implementation.

That is why I asked him to provide the exact testcase that he needs so that we can help him out

[Eranga]

Basically he try to add an array list within another. Second array list used to store the first.

Actually need a well explanation about the question too.

[coolnfunky_raj]

Ok. I am actually writing a plugin for a tool I am using at work. The plugin should parse an XML input file and return a 2D string array. The tool provides a class called Plugin, and I am extending this class to add my implementation.

I am using SAX Parser and the startElement() is triggered whenever a new tag is parsed in the XML File. I am adding the name of the tag to an ArrayList (arr). Whenever closing tag is encountered, endElement() is triggered by the parser. I am deleting the last added tag name in the ArrayList (arr). By doing this, I keep track of the path of the current tag from root tag in the input XML file. Also in the endElement() method, I am adding the current path stored in arr to arrOfArr. Hence, in the end, arrOfArr will have an array of the paths of each node from root node.

[coolnfunky_raj]

Ok. I have written a code and it works as I want it to. Can you please tell me if there are any better ways of doing it?

for #1, I did

arrOfArr.add(arr);
String tempStr[] = (String[])arr.toArray(new String[arr.size()]);
arr = new ArrayList<String>( Arrays.asList(tempStr));

This solved the problem of arrOfArr getting deleted when arr.remove() was used to delete elements.



for #2, I did

String[][] dataOutput = new String[row][col];
for(i=0; i<row; i++)
{
        tempArr = arrOfArr.get(i);
	tSize = tempArr.size();
	for(j=0; j<tSize; j++)
	{
	        dataOutput[i][j]=tempArr.get(j).toString();
	}				
}

This helped me convert ArrayList of Arraylists to String[][]