How to Choose a Random Element from a HashSet or LinkedHashSet in Java?

Choosing a Random Element from a Set

Retrieving a random element from a set can be a handy operation in various programming scenarios. Java provides two common types of sets, HashSet and LinkedHashSet, each with its unique characteristics. This article explores the approaches for selecting a random element from these sets.

HashSet

A HashSet is an unordered collection that guarantees unique elements. To pick a random entry, determine the set's size and generate a random integer within that range. Iterate through the elements, counting each one until reaching the randomly chosen index, and return the corresponding element.

<code class="java">int size = myHashSet.size();
int item = new Random().nextInt(size); // In real life, the Random object should be rather more shared than this
int i = 0;
for(Object obj : myhashSet)
{
    if (i == item)
        return obj;
    i++;
}</code>

LinkedHashSet

A LinkedHashSet extends HashSet by preserving insertion order. The same approach mentioned above can be applied to retrieve a random element, since the insertion order is maintained.

<code class="java">int size = myHashSet.size();
int item = new Random().nextInt(size); // In real life, the Random object should be rather more shared than this
int i = 0;
for(Object obj : myhashSet)
{
    if (i == item)
        return obj;
    i++;
}</code>

These methods provide a straightforward way to select a random element from a HashSet or a LinkedHashSet in Java. They can be implemented in various applications, such as generating shuffled collections, selecting items for simulation experiments, or creating pseudo-random data structures.

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