Convert an Iterable to List in Java

Write a method, that takes an Iterable as input and return the List as output.

 

Signature

public static <T> List<T> toList(final Iterable<T> iterable, final boolean skipNull)

 

Find the below working application.

IterableToList.java

package com.sample.app.collections;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class IterableToList {

	/**
	 * Converts an {@link Iterable} to a {@link List}. If skipNull is set to true,
	 * then it skip the null values while constructing the {@link List}
	 * 
	 * @param <T>
	 * @param iterable
	 * @param skipNull
	 * 
	 * @return empty list, if the {@link Iterable} is null or empty. else return a
	 *         {@link List} that contain the elements of {@link Iterable}.
	 */
	public static <T> List<T> toList(final Iterable<T> iterable, final boolean skipNull) {

		if (iterable == null) {
			return Collections.emptyList();
		}

		if (iterable instanceof List) {
			return (List<T>) iterable;
		}

		// Return empty list, if the iterator has no elements
		if (!iterable.iterator().hasNext()) {
			return Collections.emptyList();
		}

		final List<T> list = new ArrayList<>();
		for (T ele : iterable) {
			if (skipNull == true && ele == null) {
				continue;
			}
			list.add(ele);
		}

		return list;
	}

	public static void main(String[] args) {
		Set<Integer> primesSet1 = new HashSet<>(Arrays.asList(2, 3, 5, 7, null, 11, 13));

		List<Integer> list1 = toList(primesSet1, true);
		List<Integer> list2 = toList(primesSet1, false);

		System.out.println(list1);
		System.out.println(list2);

	}

}

 

Output

[2, 3, 5, 7, 11, 13]
[null, 2, 3, 5, 7, 11, 13]

 

 

 

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