Accessing data from an Arraylist stored in an Arraylist - Java

Question

I'm trying to access data from an Arraylist that is stored in an Arraylist. I'm sure there is a really easy way to do this and I don't want to waste anyone's time but I've tried lots of ways and can't seem to find the answer anywhere. Any help would be really appreciated.

This is my code for creating the Arrays.

    public ArrayList SGenresMaster = new ArrayList(new ArrayList());
    public ArrayList S1Genres = new ArrayList();
    public ArrayList S2Genres = new ArrayList();
    public ArrayList S3Genres = new ArrayList();        


    public void accessArrays(){

    SGenresMaster.add(S1Genres);
    SGenresMaster.add(S2Genres);  
    SGenresMaster.add(S3Genres);

    }

Basically i need to be able to access any index of S1Genres using SgenresMaster.

So far I've only managed to get the data out as a long string so I thought I'd post my current method for getting the data I need, as i thought it would probably make the pro's here cringe/laugh.

    createarray(SGenresMaster.get(i).toString());

    public ArrayList createarray(String string){

    String sentence = string;
    String[] words = sentence.split(", ");
    ArrayList temp = new ArrayList();
    int b = 0;
    for (String word : words)
    {
        if (b == 0){
            //Delete First bracket
            temp.add(word.substring(1,word.length()));
            System.out.println("First Word: " + temp);
        }
        else{
            temp.add(word.substring(0,word.length()));
            System.out.println("Middle Word: " + temp);
        }
        b++;

    }
    //Delete last bracket
    String h = String.valueOf(temp.get(temp.size() - 1));
    temp.add(h.substring(0,h.length() - 1));
    temp.remove(temp.size() - 2);


    System.out.println("final:" + temp);

    return temp;
}

I think your main problem is using raw array lists, use the <> notation to indicate what they contain — Richard Tingle
– Richard Tingle, Commented Aug 31, 2013 at 18:23
No reason apart from not knowing I need to. Cheers for the help. — Greg King
– Greg King, Commented Aug 31, 2013 at 18:30
@GregKing Apart from solving this problem it also avoids having to cast things you .get() from array lists and gives you type safety. All in all, always use the non raw version — Richard Tingle
– Richard Tingle, Commented Aug 31, 2013 at 18:32

Community · Accepted Answer · 2017-05-23 11:49:52Z

2

Using raw generic types is a bad practice. You lose all the advantages of generics that way.

That said, for illustration if your sublists are made up of Strings:

        ArrayList<List<String>> SGenresMaster = new ArrayList<List<String>>();
        ArrayList<String> S1Genres = new ArrayList<String>();
        ArrayList<String> S2Genres = new ArrayList<String>();
        ArrayList<String> S3Genres = new ArrayList<String>();

        SGenresMaster.add(S1Genres);
        SGenresMaster.add(S2Genres);  
        SGenresMaster.add(S3Genres);


    SGenresMaster.get(0).get(0); //gets the first element of S1Generes

edited May 23, 2017 at 11:49

CommunityBot

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answered Aug 31, 2013 at 18:25

rocketboy

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3 Comments

Greg King Over a year ago

Perfect thank-you I knew there was a really easy way to do this

Richard Tingle Over a year ago

Aren't there supposed to be <String> or similar on both sides or <> notation in java 7. Although oddly my compiler seems fine with it

rocketboy Over a year ago

@RichardTingle You are right. But it is not a compilation error, though most compilers will generate warnings. Fixed for clarity.

Nikola Despotoski · Accepted Answer · 2013-08-31 18:25:03Z

0

I hope your got your question right:

for(ArrayList<String> arr: SGenresMaster){
    //arr can be any array from SGenresMaster
    for(String s : arr){
      //do something
   }

}

or

 SGenresMaster.get(index).get(someOtherIndex);

answered Aug 31, 2013 at 18:25

Nikola Despotoski

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