ArrayList of ArrayLists.. Unable to refer to them multiple times

Question

Here is a particular method I have written:

class A {

    private static ArrayList<ArrayList<Integer>> inputTerms = 
                                              new ArrayList<ArrayList<Integer>();

    public static void method1(ArrayList<Integer> terms) {

        int N = terms.size();
        for (int i = 0; i < N - 1; i++) {
            for (int j = i + 1; j < N; j++) {
                ArrayList<Integer> clauses = new ArrayList<Integer>();
                clauses.add(-terms.get(i));
                clauses.add(-terms.get(j));
                inputTerms.add(clauses);
            }
        }
    }
}

In my main function, i have the following code:

for (int i=0; i<N-1; i++){ 
   ArrayList<Integer> firstdiagonalTerms = new ArrayList<Integer>(); 
   for (int j=0; j<N-i; j++){ 
      firstdiagonalTerms.add(variable[j][i+j]); 
   } 
   method1(firstdiagonalTerms);
}

I have 4 such double for-loops in my main function where i call method1 for different iterations. However, while the 1st for-loop gives the approppriate answer, the minute i declare an ArrayList inside my 2nd for loop, my inputTerns variable gets set to null. How do i overcome this?

John Eipe · Accepted Answer · 2012-09-04 18:37:19Z

I don't understand what you are trying to achieve here. But you can definitely create ArrayList of ArrayLists.

public class Testapp {

static ArrayList<ArrayList<Integer>> inputTerms = new ArrayList<ArrayList<Integer>>();

public static void main(String[] args) {
    int outerlist = 3;
    int innerlist = 5;
    for(int i=0; i<outerlist; i++)
    {
        ArrayList<Integer> list = new ArrayList<Integer>(); 
        for(int j=0; j<innerlist; j++)
        {
            list.add(j);
        }
        inputTerms.add(list);
    }

    Iterator outi = inputTerms.iterator();
    while(outi.hasNext()){
        ArrayList<Integer> temp = (ArrayList<Integer>)outi.next();
        Iterator ini = temp.iterator();
        while(ini.hasNext()){
            System.out.print(ini.next());
        }
        System.out.println();
    }
}
}

Output:

01234 
01234 
01234

xpda · Accepted Answer · 2013-01-21 17:27:18Z

1

I recommend you use ArrayList<Integer[]> instead of another ArrayList. You might lose some stuff without ArrayList, but it's the only way.

edited Jan 21, 2013 at 17:27

xpda

15.9k8 gold badges54 silver badges83 bronze badges

answered Sep 4, 2012 at 18:16

Ewen

1,0262 gold badges17 silver badges25 bronze badges

2 Comments

user1646637 Over a year ago

sorry, could you elaborate a bit?

Ewen Over a year ago

Sorry that was my bad i meant arrarylist<integer[]>

Collectives™ on Stack Overflow

ArrayList of ArrayLists.. Unable to refer to them multiple times

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related