Demonstration that objects within a list are passed by reference to any other list they're appended to. In other words: List 1 = [ Object1, Object2, Object3 ... ObjectN ] List 2 = [] List 2 .add ( some object from List 1 ) List 2 will have a reference to the same object in List 1.

ListReference.java

import java.util.List;
import java.util.ArrayList;
import java.util.Collection;

public class ListReference{
	public static int id = 0;
	protected static class MyLittleObject{
		
		public int val;
		public MyLittleObject(){this.val=ListReference.id; ListReference.id +=1; }
	}
	public static void main(String[] args) {
		List<MyLittleObject> outer = new ArrayList<MyLittleObject>();		
		for(int i=0; i < 10; i++){
			outer.add(new MyLittleObject());
		}
		//Print it
		System.out.println("initial array: ");
		for(final MyLittleObject o : outer){
			System.out.print("|" + o + "( " + o.val + ") | ");
		}
		System.out.println("");
		ListReference.func1(outer);
	}

	public static void func1(Collection<MyLittleObject> friends){
		//We have this list of things and now we're going to pass it over somewhere else
		List<MyLittleObject> chunk = new ArrayList<MyLittleObject>();
		List<MyLittleObject> toAppendTo = new ArrayList<MyLittleObject>();

		for(final MyLittleObject o : friends){
			chunk.add(o);
			if(chunk.size() == 3){ //minimal example
				toAppendTo.addAll(ListReference.func2(chunk));
				chunk.clear();
			}
		}

		if(!chunk.isEmpty())
			toAppendTo.addAll(ListReference.func2(chunk));

		//Now print the toAppendTo
		System.out.println("Array that will be returned");
		for(final MyLittleObject o : toAppendTo)
			System.out.print("|" + o + "( " + o.val + ") | ");
		System.out.println("");

		//What's in chunk?
		System.out.println("Chunk array");
		for(final MyLittleObject o : chunk)
			System.out.print("|" + o + "( " + o.val + ") | ");
		System.out.println("");

	}

	public static Collection<MyLittleObject> func2(Collection<MyLittleObject> chunks){
		List<MyLittleObject> hold = new ArrayList<MyLittleObject>();
		//Take the chunk and put some of it into hold
		for(final MyLittleObject o : chunks ){
			if(o.val % 3 == 0)
				hold.add(o);
		}
		//Return the list.
		return hold;
	}
}