Creational Design Patterns: Prototype Pattern [Snippet]

Creational Design Patterns: Prototype Pattern [Snippet]

Want to learn more about using creational design patterns? Check out this tutorial on how to use the prototype design pattern in Java to learn more!

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The prototype pattern is used to create a copy of an object. This pattern can be really useful, especially when creating an object from scratch. In comparison with the builder , factory , and abstract factory patterns, it does not create an object from scratch — it clones it.

However, with the  singleton pattern, it creates multiple copies of an instance whilst the singleton has to ensure that only one will exist.

Imagine the scenario of an object that, which in order to be created, requires a very resource-intensive method. It can be a database query with many joins or even the result of a federated search.

We want those data to be processed by various algorithms using one thread per algorithm. Every thread should have its own copy of the original instance, since using the same object will result in inconsistent results.

Here, we have an interface for representing the result of a search:

package com.gkatzioura.design.creational.prototype;

public interface SearchResult {

    SearchResult clone();

    int totalEntries();

    String getPage(int page);
}

And, we have the implementation of the SearchResult  and  the   FederatedSearchResult .

package com.gkatzioura.design.creational.prototype;

import java.util.ArrayList;
import java.util.List;

public class FederatedSearchResult implements SearchResult {

    private List<String> pages = new ArrayList<String>();

    public FederatedSearchResult(List<String> pages) {
        this.pages = pages;
    }

    @Override
    public SearchResult clone() {

        final List<String> resultCopies = new ArrayList<String>();
        pages.forEach(p->resultCopies.add(p));
        FederatedSearchResult federatedSearchResult = new FederatedSearchResult(resultCopies);
        return federatedSearchResult;
    }

    @Override
    public int totalEntries() {
        return pages.size();
    }

    @Override
    public String getPage(int page) {
        return pages.get(page);
    }
}

We can use the clone method and create as many copies as we need of this object.

You can find the source code on GitHub .