[ACCEPTED]-Split larger collection (Collections, Arrays, List) into smaller collections in Java and also keep track of last one returned-collections

Maybe I don't understand the question, but 17 this is part of List:

List<E> subList(int fromIndex, int toIndex)

Returns a view of the 16 portion of this list between the specified 15 fromIndex, inclusive, and toIndex, exclusive. (If 14 fromIndex and toIndex are equal, the returned 13 list is empty.) The returned list is backed 12 by this list, so non-structural changes 11 in the returned list are reflected in this 10 list, and vice-versa. The returned list 9 supports all of the optional list operations 8 supported by this list.

This method eliminates 7 the need for explicit range operations (of 6 the sort that commonly exist for arrays). Any 5 operation that expects a list can be used 4 as a range operation by passing a subList 3 view instead of a whole list. For example, the 2 following idiom removes a range of elements 1 from a list:

list.subList(from, to).clear();

docs.oracle.com/javase/1.5.0/docs/api/java/util/List.html

This is simple: just use Lists.partition() from Guava. If 2 I understand what you want correctly, it's 1 exactly what it does.

private int runs = 0;

public void setRunsOneMore() {
    runs++;
}

    public void setRunsOneLess() {
    runs--;
}

public Collection<Comment> getCommentCollection() {
    commentCollection = movie.getCommentCollection();
    Collection[] com = split((List<Comment>) commentCollection,4);
    try{
        return com[runs];
     } catch(ArrayIndexOutOfBoundsException e) {
       runs = 0;
      }
    return com[runs];
}

public Collection[] split(List<Comment> list, int size){

     int numBatches = (list.size() / size) + 1;
     Collection[] batches = new Collection[numBatches];
     Collection<Comment> set = commentCollection;

     for(int index = 0; index < numBatches; index++) {
         int count = index + 1;
         int fromIndex = Math.max(((count - 1) * size), 0);
         int toIndex = Math.min((count * size), list.size());
         batches[index] = list.subList(fromIndex, toIndex);
     }

     return batches;
 }

Setting the current "run" with the next 1 & previous button actions

public String userNext() {
    userReset(false);
    getUserPagingInfo().nextPage();
    movieController.setRunsOneMore();
    return "user_movie_detail";
}

public String userPrev() {
    userReset(false);
    getUserPagingInfo().previousPage();
    movieController.setRunsOneLess();
    return "user_movie_detail";
}

I'm not entirely sure what you're asking... do 14 you want to remove the first 4 items from 13 the source Collection before returning them, so that 12 you get the next 4 the next time you call 11 the method? If so, you could just use the 10 Iterator:

Iterator<Comment> iter = commentCollection.iterator();
while (iter.hasNext() && group.size() < 4) {
  group.add(iter.next());
  iter.remove();
}

By doing this, though, you'd be destroying 9 the movie object's collection of comments (unless 8 it returns a copy of that collection each 7 time, in which case the above wouldn't work 6 at all). I'm guessing you're trying to 5 do something like paging, in which case 4 I'd suggest doing something different like 3 partitioning a List of comments with size 4 and keeping 2 track of a current index (the page) in that 1 partition list.

public static <E extends Object> List<List<E>> split(Collection<E> input, int size) {\n
    List<List<E>> master = new ArrayList<List<E>>();
    if (input != null && input.size() > 0) {
        List<E> col = new ArrayList<E>(input);
        boolean done = false;
        int startIndex = 0;
        int endIndex = col.size() > size ? size : col.size();
        while (!done) {
            master.add(col.subList(startIndex, endIndex));
            if (endIndex == col.size()) {
                done = true;
            }
            else {
                startIndex = endIndex;
                endIndex = col.size() > (endIndex + size) ? (endIndex + size) : col.size();
            }
        }
    }
    return master;
}

0

You can create a separate sublist that is 2 a deep copy of the original list using the 1 ArrayList constructor.

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

class Scratch {
    public static void main(String[] args) {
        final List<String> parent = new ArrayList<>();
        parent.add("One");
        parent.add("Two");
        parent.add("Three");

        // using the ArrayList constructor here
        final List<String> copy = new ArrayList<>(parent.subList(0, 2));
   
        // modifying the new list doesn't affect the original
        copy.remove(0);

        // outputs:
        // parent: [One, Two, Three]
        // copy:   [Two]
        System.out.println("parent: " + parent);
        System.out.println("copy:   " + copy);
    }
}

You can use Vector.remove(collection), example:

public Collection<Comment> getCommentCollection() {
    commentCollection = movie.getCommentCollection();
    Vector<Comment> group = new Vector<Comment>();
    for (Comment com:commentCollection){
        group.add(com);
    if(group.size() == 4){
        break;
    }
    }
    movie.getCommentCollection().remove(commentCollection);
    return commentCollection;
}

assuming 1 movie.getCommentCollection() is also a vector

here is my implementation. hope it helps!

dependencies 1 CollectionUtils and Lists to see: https://mvnrepository.com/artifact/org.apache.commons/commons-lang3/

/**
 * efficient collection partition
 *
 * @param baseCollection base collection to split
 * @param maxSize max element size of each sublist returned
 * @param balancing whether each of sublists returned needs size balancing
 * @return list of sublists, whose order bases on the base collection's iterator implementation
 * @since 2020/03/12
 */
public static <T> List<List<T>> partition(final Collection<T> baseCollection, int maxSize, boolean balancing) {

    if (CollectionUtils.isEmpty(baseCollection)) {
        return Collections.emptyList();
    }

    int size = baseCollection.size() % maxSize == 0 ? baseCollection.size()/maxSize : baseCollection.size()/maxSize+1;
    if (balancing) {
        maxSize = baseCollection.size() % size == 0 ? baseCollection.size()/size : baseCollection.size()/size+1;
    }
    int fullElementSize = baseCollection.size() % size == 0 ? size : baseCollection.size() % size;

    List<List<T>> result = Lists.newArrayListWithExpectedSize(size);
    Iterator<T> it = baseCollection.iterator();
    for (int i = 0; i < size; i++) {
        if (balancing && i == fullElementSize) {
            maxSize--;
        }
        maxSize = Math.min(maxSize, baseCollection.size()-i*maxSize);

        List<T> subList = Lists.newArrayListWithExpectedSize(maxSize);
        for (int i1 = 0; i1 < maxSize; i1++) {
            if (it.hasNext()) {
                subList.add(it.next());
            } else {
                break;
            }
        }
        result.add(subList);
    }

    return result;
}