Java Collection Random Element getRandom(Collection collection)

Description

get Random

License

Apache License

Declaration

public static <V> V getRandom(Collection<V> collection) 

Method Source Code

//package com.java2s;
/**/*from ww w .j a v  a2s.  co m*/
 * Copyright (C) 2012 Philip W. Sorst <philip@sorst.net>
 * and individual contributors as indicated
 * by the @authors tag.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.Collection;

import java.util.Iterator;

public class Main {
    public static <V> V getRandom(Collection<V> collection) {

        if (collection.isEmpty()) {
            return null;
        }

        int randIdx = (int) Math.round(Math.random() * (collection.size() - 1));
        int count = 0;
        Iterator<V> iterator = collection.iterator();
        while (iterator.hasNext()) {
            V current = iterator.next();
            if (count == randIdx) {
                return current;
            }
            count++;
        }

        throw new RuntimeException("Shouldn't happen");
    }

    /**
     * Nullsafe check if a collection is empty.
     * 
     * @param obj
     *            Null or a subclass of Collection.
     * @throws IllegalArgumentException
     *             Thrown if obj is not null and not an instance of Collection.
     */
    public static boolean isEmpty(Object obj) {

        if (obj == null) {
            return true;
        }

        if (obj instanceof Collection) {
            return ((Collection<?>) obj).isEmpty();
        }

        throw new IllegalArgumentException("Given Object was not a collection");
    }
}

Related

1. chooseElement(Collection elements, T alternative)
2. chooseRandomThing(Collection possibleroutes)
3. chooseWithoutCheck(Collection collection, long seed)
4. generateMetricsDataWithAllWrongTypes(String metricPostfix, boolean generateRandomTenant, long collectionTime)
5. generateMetricsDataWithPartialWrongTypes(String metricPostfix, boolean generateRandomTenant, long collectionTime)
6. getRandomNumber(Collection collection, int number)
7. nextItem(Collection items, Random random)
8. oneOf(Collection array)
9. peekRandom(Collection collection, Random rnd)