Find the common element type of the given Collection, if any. - Java java.util

Java examples for java.util:Collection Search

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Description

Find the common element type of the given Collection, if any.

Demo Code

/*/*  w w w. j a  va  2s.  c o m*/
 * Copyright 2002-2015 the original author or authors.
 *
 * 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.
 */
//package com.java2s;
import java.util.*;

public class Main {
    public static void main(String[] argv) {
        Collection collection = java.util.Arrays.asList("asdf",
                "java2s.com");
        System.out.println(findCommonElementType(collection));
    }

    /**
     * Find the common element type of the given Collection, if any.
     *
     * @param collection the Collection to check
     * @return the common element type, or {@code null} if no clear
     * common type has been found (or the collection was empty)
     */
    public static Class<?> findCommonElementType(Collection<?> collection) {
        if (isEmpty(collection)) {
            return null;
        }
        Class<?> candidate = null;
        for (Object val : collection) {
            if (val != null) {
                if (candidate == null) {
                    candidate = val.getClass();
                } else if (candidate != val.getClass()) {
                    return null;
                }
            }
        }
        return candidate;
    }

    /**
     * Return {@code true} if the supplied Collection is {@code null} or empty.
     * Otherwise, return {@code false}.
     *
     * @param collection the Collection to check
     * @return whether the given Collection is empty
     */
    public static boolean isEmpty(Collection<?> collection) {
        return (collection == null || collection.isEmpty());
    }

    /**
     * Return {@code true} if the supplied Map is {@code null} or empty.
     * Otherwise, return {@code false}.
     *
     * @param map the Map to check
     * @return whether the given Map is empty
     */
    public static boolean isEmpty(Map<?, ?> map) {
        return (map == null || map.isEmpty());
    }
}

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