How do I create an empty collection object?

Sometimes you need to return an empty collection from your Java methods. The java.util.Collections utility class have three different static constants for creating empty List, Set and Map.

• Collections.EMPTY_LIST
• Collections.EMPTY_SET
• Collections.EMPTY_MAP

There are also methods when you want to create type-safe empty collections.

• Collections.emptyList()
• Collections.emptySet()
• Collections.emptyMap()

Bellow it the code example.

package org.kodejava.util;

import java.util.*;

public class EmptyCollectionDemo {
    public static void main(String[] args) {
        List list = Collections.EMPTY_LIST;
        System.out.println("list.size()  = " + list.size());
        Set set = Collections.EMPTY_SET;
        System.out.println("set.size()   = " + set.size());
        Map map = Collections.EMPTY_MAP;
        System.out.println("map.size()   = " + map.size());

        // For the type-safe example use the following methods.
        List<String> strings = Collections.emptyList();
        System.out.println("strings.size = " + strings.size());

        Set<Long> longs = Collections.emptySet();
        System.out.println("longs.size() = " + longs.size());

        Map<String, Date> dates = Collections.emptyMap();
        System.out.println("dates.size() = " + dates.size());
    }
}

The output are:

list.size()  = 0
set.size()   = 0
map.size()   = 0
strings.size = 0
longs.size() = 0
dates.size() = 0