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package com.groupbyinc.common.util;

import com.groupbyinc.common.util.exception.GroupByUtilException;

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * Java utilities
 *
 * @author Alan Czajkowski
 */
public final class JavaUtils {

    private JavaUtils() {
        // not publicly instantiable
    }

    /**
     * Return a non-null {@link List}.
     *
     * @param list
     *         a list (can be null)
     *
     * @return {@link List} a non-null immutable list
     */
    public static  List notNull(List list) {
        return list == null ? Collections.emptyList() : list;
    }

    /**
     * Return a non-null {@link Set}.
     *
     * @param set
     *         a set (can be null)
     *
     * @return {@link Set} a non-null immutable set
     */
    public static  Set notNull(Set set) {
        return set == null ? Collections.emptySet() : set;
    }

    /**
     * Return a non-null {@link Collection}.
     *
     * @param collection
     *         a collection (List or Set, can be null)
     *
     * @return {@link Collection} a non-null immutable collection
     */
    public static  Collection notNull(Collection collection) {
        if (collection instanceof List) {
            return notNull((List) collection);
        } else if (collection instanceof Set) {
            return notNull((Set) collection);
        }

        throw new GroupByUtilException("Not a List or Set");
    }

    /**
     * Return a non-null {@link Map}.
     *
     * @param map
     *         a map (can be null)
     *
     * @return {@link Map} a non-null immutable map
     */
    public static  Map notNull(Map map) {
        return map == null ? Collections.emptyMap() : map;
    }

}