Java List Sub List subList(List initial, int threshold)

Description

creates a list of lists, each of which is up to the value of threshold in length.

License

Apache License

Parameter

Parameter	Description
T	a parameter
initial	a parameter
threshold	a parameter

Declaration

public static <T> List<List<T>> subList(List<T> initial, int threshold) 

Method Source Code

//package com.java2s;
//License from project: Apache License 

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

public class Main {
    /**//from ww w  .  ja va 2  s . c om
     * creates a list of lists, each of which is up to the value of threshold in length.
     *
     * @param <T>
     * @param initial
     * @param threshold
     * @return
     */
    public static <T> List<List<T>> subList(List<T> initial, int threshold) {
        ArrayList<List<T>> list = new ArrayList<List<T>>();

        if (initial != null) {

            if (initial.size() <= threshold) {
                list.add(initial);
            } else {
                int factor = initial.size() / threshold;

                for (int i = 0; i < (factor + 1); i++) {
                    list.add(limit(initial, i * threshold, threshold));
                }
            }
        }

        return list;
    }

    /**
     * Performs a safe limit on a given list. checks wether offset and amount are within bounds. If the offset is out of bounds, limit will automatically adapt by
     * substracting amount from the lists size. If amount is larger than initial's size, initia will be returned in its entirity.
     *
     *
     * @param <T>
     * @param initial
     * @param offset
     * @param amount
     * @return a safely limited version of initial.
     */
    public static <T> List<T> limit(List<T> initial, int offset, int amount) {

        if (isNullOrEmpty(initial)) {
            return new ArrayList<T>();
        } else if (amount > initial.size()) {
            return initial;
        }

        int lower = (int) ((offset < initial.size()) ? offset
                : (((initial.size() - offset) < 0) ? 0 : (initial.size() - offset)));
        int upper = amount + lower;
        List<T> resultSet = new ArrayList<T>(
                initial.subList((lower > initial.size()) ? (initial.size() - amount) : lower,
                        (upper > initial.size()) ? initial.size() : upper));

        return resultSet;
    }

    /**
     * Performs a thorough null and empty check. This asserts that a given collection is null, empty or only consists of null values.
     *
     * @param col
     * @return asserts that a given collection is null, empty or only consists of null values.
     */
    public static boolean isNullOrEmpty(Collection<?> col) {

        if ((col == null) || col.isEmpty())
            return true;
        else {

            try {

                for (Iterator<?> iterator = col.iterator(); iterator.hasNext();) {

                    if (iterator.next() != null) {
                        return false;
                    }
                }
            } catch (NullPointerException e) { // guard against null during concurrent modifications
                return false;
            }

            return true;
        }
    }
}

Related

1. subList(List list, int fromIndex)
2. subList(List list, int skip, int top)
3. subList(List list, int start, int end)
4. subList(List list, int begin, int end)
5. subList(List lst, Collection indices)
6. subList(List input, int startIndex, int count)
7. subList(List input, int startIndex, int count)
8. subList(List it, int offset, int limit)
9. sublist(List l, int fromIndex, int toIndex)