Method to convert a List Collection to Iterable object. - Java java.util

Description

Method to convert a List Collection to Iterable object.

Demo Code

import java.lang.reflect.Array;
import java.util.*;

public class Main{
    public static void main(String[] argv){
        Object collection = "book2s.com";
        System.out.println(toIterable(collection));
    }//w ww  .j a  va2s  . c  om
    private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory
            .getLogger(CollectionUtilities.class);
    /**
     * Method to convert a List Collection to Iterable object.
     * @param <T> generic type.
     * @param collection the Collection.
     * @return the Iterable object.
     */
    @SuppressWarnings("unchecked")
    public static <T> Iterable<T> toIterable(final Object collection) {
        if (isCollection(collection)) {
            //if(collection instanceof List)return toSet((List<T>)collection);
            if (collection instanceof Set)
                return toList(((Set<T>) collection));
            if (collection instanceof Object[])
                return Arrays.asList((T[]) collection);
            if (collection instanceof Iterator) {
                return new Iterable<T>() {
                    @Override
                    public Iterator<T> iterator() {
                        return (Iterator<T>) collection;
                    }
                };
            } else {
                return new Iterable<T>() {
                    @Override
                    public Iterator<T> iterator() {
                        return null;
                    }
                };
            }
        } else {
            logger.error("The object:" + collection
                    + " is not a Collection");
            return new Iterable<T>() {
                @Override
                public Iterator<T> iterator() {
                    return null;
                }
            };
        }
    }
    /**
     * Method to check if a Object is a Collection or not.
     * @param ob the Object to inspect.
     * @return if true the class extend or implememnt Collection.
     */
    public static boolean isCollection(Object ob) {
        return ob instanceof Collection || ob instanceof Map;
        //return ob != null && isClassCollection(ob.getClass());
    }
    /**
     * Method to convert a Collection to a List collection.
     * @param <T> generic type.
     * @param collection the Collection object.
     * @return the List object.
     */
    @SuppressWarnings("unchecked")
    public static <T> List<T> toList(Object collection) {
        if (isCollection(collection)) {
            if (collection instanceof Enumeration)
                return Collections.list((Enumeration<T>) collection);
            if (collection instanceof TreeSet)
                return new ArrayList<>((TreeSet<T>) collection);
            //if(collection instanceof Set) return SetUtilities.toList((Set<T>) collection);
            if (collection instanceof Iterable) {
                if (collection instanceof List)
                    return (List<T>) collection;
                else {
                    List<T> list = new ArrayList<>();
                    for (T e : (Iterable<T>) collection) {
                        list.add(e);
                    }
                    return list;
                }
            }
            if (collection instanceof Object[])
                return ArrayUtilities.toList((T[]) collection);
            if (collection instanceof Iterator) {
                List<T> list = new ArrayList<>();
                Iterator<T> iterator = (Iterator<T>) collection;
                while (iterator.hasNext()) {
                    list.add(iterator.next());
                }
                return list;
            } else
                return new ArrayList<>();
        } else {
            logger.error("The object:" + collection
                    + " is not a Collection");
            return new ArrayList<>();
        }
    }
}

• Previous
• Next

Related Tutorials

• Convert a Collection of T to a sorted List of T.
• Convert Collection to HashSet
• Converts a collection to a list by either casting or creating a concrete list depending on the type of collection given.
• Method to convert a Collection to Iterator object.
• Method to convert a Collection to a List collection.