Java List Clone cloneList(final List l, final int n)

Description

Creates a list containing the specified list N times in a row.

License

Open Source License

Parameter

Parameter	Description
l	List to be cloned. Must not be <code>null</code>.
n	How many times should the list be cloned. Must be non-negative.

Return

Flat list containing the input list N times in a row. If the input list is empty, or N = 0, the result is an empty list.

Declaration

public static <T> List<T> cloneList(final List<T> l, final int n) 

Method Source Code

//package com.java2s;
/*// www .ja va 2  s  . c o m
 *  Copyright (C) 2010 vektor
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;

import java.util.List;

public class Main {
    /**
     * Creates a list containing the specified list N times in a row.
     *
     * @param l List to be cloned. Must not be <code>null</code>.
     * @param n How many times should the list be cloned. Must be non-negative.
     * @return Flat list containing the input list N times in a row. If the input
     * list is empty, or N = 0, the result is an empty list.
     */
    public static <T> List<T> cloneList(final List<T> l, final int n) {
        if (l == null) {
            throw new IllegalArgumentException("The list to be cloned must not be null.");
        }
        if (n < 0) {
            throw new IllegalArgumentException("When cloning a list, N must be non-negative (" + n + ")");
        }
        if (n == 0 || isEmpty(l)) {
            return Collections.emptyList();
        }

        final List<T> ret = new ArrayList<T>();
        for (int i = 0; i < n; i++) {
            ret.addAll(l);
        }
        return ret;
    }

    /**
     * Checks whether the collection is empty, that means NULL or empty as in "no elements within".
     *
     * @param <T>
     * @param c Collection to check.
     * @return True if the collection is NULL or contains no elements.
     */
    public static <T> boolean isEmpty(final Collection<T> c) {
        return c == null || c.isEmpty();
    }

    /**
     * Checks whether the string is empty, that means NULL or equal to "".
     *
     * @param s String to check.
     * @return True if the string is NULL or has no characters.
     */
    public static boolean isEmpty(final String s) {
        return s == null || "".equals(s);
    }
}

Related

1. clone(List