Storing objects in arraylist

Question

I have a small issue when I run into while using arraylists in Java. Essentially I am hoping to store an array in an arraylist. I know that arraylists can hold objects, so it should be possible, but I am not sure how.

For the most part my arraylist (which is parsed from a file) is just holding one character as a string, but once in a while it has a series of characters, like this:

    myarray
0    a
1    a
2    d
3    g
4    d
5    f,s,t
6    r

Most of the time the only character I would care about in the string residing at position 5 is the f but occasionally I may need to look at the s or the t as well. My solution to this is to make an array like this:

      subarray
0     f 
1     s
2     t

and store subarray in position 5 instead.

    myarray
0    a
1    a
2    d
3    g
4    d
5    subarray[f,s,t]
6    r

I tried to do this with this code:

 //for the length of the arraylist
 for(int al = 0; al < myarray.size(); al++){
      //check the size of the string
      String value = myarray.get(al);
      int strsz = value.length();
      prse = value.split(dlmcma);
      //if it is bigger than 1 then use a subarray
      if(strsz > 1){
          subarray[0] = prse[0];
          subarray[1] = prse[1];
          subarray[2] = prse[2];
      }
      //set subarray to the location of the string that was too long
      //this is where it all goes horribly wrong
      alt4.set(al, subarray[]);
  }

This isn't working the way I would like though. It won't allow me to .set(int, array). It only allows .set(int, string). Does anyone have suggestions?

You do realize that a String is a char[] with methods around, right? Just use a List<String> with values like "a" or "fst", there's no need for separators and splitting if what you're interested in is individual characters. — Frank Pavageau
– Frank Pavageau, Commented Oct 17, 2012 at 21:37

James McCracken · Accepted Answer · 2012-10-17 21:05:32Z

2

The easiest approach would be to have an ArrayList of ArrayList.

ArrayList<ArrayList<String>> alt4 = new ArrayList<ArrayList<String>>();

However, this probably isn't the best solution. You may want to rethink your data model and look for a better solution.

answered Oct 17, 2012 at 21:05

James McCracken

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1 Comment

Stephopolis Over a year ago

Yeah. I will be rethinking it today. Thanks

Yogendra Singh · Accepted Answer · 2012-10-17 21:05:46Z

0

Just change alt4.set(al, subarray[]); to

         alt4.add(subarray);

I assume alt4 is another defined ArrayList<String[]>. If not, define it as below:

        List<String[]> alt4= new ArrayList<String[]>();

or

        ArrayList<String[]> alt4= new ArrayList<String[]>();

answered Oct 17, 2012 at 21:05

Yogendra Singh

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Comments

amphibient · Accepted Answer · 2012-10-17 21:07:05Z

0

My guess is that you are declaring alt4 as List<String> and that's why it is not letting you set an array of String as a list element. You should declare it as List<String[]> and is each element is only singular, simply set it as the 0th element of the String[] array before adding it to the list.

answered Oct 17, 2012 at 21:07

amphibient

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Cratylus · Accepted Answer · 2012-10-17 21:08:55Z

0

You could switch to:

List<List<Character>> alt4 = new ArrayList<List<Character>>();

answered Oct 17, 2012 at 21:08

Cratylus

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Festus Tamakloe · Accepted Answer · 2012-10-17 21:25:06Z

May be this is what you want to get

public class Tester {

    List<String> myArrays = Arrays.asList(new String[] { "a", "a", "d", "g", "d", "f,s,t", "r" });

    ArrayList<ArrayList<String>> alt4 = new ArrayList<ArrayList<String>>();

    private void manageArray() {
        // for the length of the arraylist
        ArrayList<String> subarray = new ArrayList<String>();
        for(int al = 0; al < myArrays.size(); al++) {
            // check the size of the string
            String value = myArrays.get(al);
            int strsz = value.length();
            String prse[] = value.split(",");
            // if it is bigger than 1 then use a subarray
            if(strsz > 1) {
                for(String string : prse) {
                    subarray.add(string);
                }
            }
            // set subarray to the location of the string that was too long
            // this is where it all goes horribly wrong
            alt4.set(al, subarray);
        }

    }
}

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