iterate declared arraylists in java

Question

I have a similar problem that is described below:

The difference is that in my class I have elements that are ArrayLists (all ArrayLists contains elements of the same type), not primitive types.

I would like to know whether it is possible to iterate elements and inside this loop iterate declared ArrayList?

Can you give an example? Your question is a little vague. What do the ArrayLists contain ? Other reference types? — Hunter McMillen
– Hunter McMillen, Commented Dec 18, 2012 at 15:46
So you clarify: You have an ArrayList of some reference type A and you want to iterate over your ArrayList so you can access each of these A objects ? — Hunter McMillen
– Hunter McMillen, Commented Dec 18, 2012 at 15:48
I am sure the solution to original problem would be easier compared to problem itself. So key here is to understand what he wants :) — Viral Patel
– Viral Patel, Commented Dec 18, 2012 at 15:50
Yes, exactly. Similarly like in the link in the post, but instead of ints I have ArrayLists. And I would like to iterate over them. — JosephConrad
– JosephConrad, Commented Dec 18, 2012 at 15:50

Hunter McMillen · Accepted Answer · 2012-12-18 15:54:59Z

2

You can directly iterate over ArrayLists, so your example is different from the link you posted, they needed to use reflection to iterate them because they weren't already grouped into a container:

class MyClass {
   public static ArrayList<A> myList = new ArrayList<>(
                                       Arrays.asList(new A[]{ A1, A2, ..., AN);

   public static void main(String[] args) {
       // iterate over your list
       for(A a : myList) {
          // do something with A object
       }
   }
}

answered Dec 18, 2012 at 15:54

Hunter McMillen

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1 Comment

JosephConrad Over a year ago

Thanks! Indeed it looks like a sufficient solution. Anyway, now I will try to code this. Once again thanks a lot.

Avinash Nair · Accepted Answer · 2012-12-18 18:58:48Z

There are several ways to iterate over an ArrayList<Type> of a refrence type I found the following ways useful, you could try out yourself.

A. The most common/simple way of doing it, by using a counter to list its elements

    ArrayList<Person> persons = new ArrayList<Person>();
    //Add some person objects to the list
    for(int i=0;i<persons.size();i++){    
    System.out.println(persons.get(i));
    }

B. Using an iterator

   for (Iterator i = persons.iterator(); i.hasNext();) {
     Object listElement = i.next();
     System.out.println(listElement);
   }

C. A For/in loop

  for (Person listElement : persons) {
     System.out.println(listElement); 
   }

You could possibly use any of the 3 methods to get your work done, but it is recommended to use the last method which is the For/in loop since you won't have to use a counter (usually called i or count) or a Iterator

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