What are helper objects in java?

Question

I come across few of the times called helper objects... can anybody elaborate what are those helper objects and why do we need them?

Answer 1

Some operations which are common to a couple of classes can be moved to helper classes, which are then used via object composition:

public class OrderService {     private PriceHelper priceHelper = new PriceHelper();      public double calculateOrderPrice(order) {         double price = 0;         for (Item item : order.getItems()) {             double += priceHelper.calculatePrice(item.getProduct());         }     } }  public class ProductService {     private PriceHelper priceHelper = new PriceHelper();      public double getProductPrice(Product product) {         return priceHelper.calculatePrice(product);     } } 

Using helper classes can be done in multiple ways:

• Instantiating them directly (as above)
• via dependency injection
• by making their methods static and accessing them in a static way, like IOUtils.closeQuietly(inputStream) closes an InputStream wihtout throwing exceptions.
• at least my convention is to name classes with only static methods and not dependencies XUtils, and classees that in turn have dependencies / need to be managed by a DI container XHelper

(The example above is just a sample - it shouldn't be discussed in terms of Domain Driven Design)