Your Java method should warn about NPE while coding itself

Define your method is such way that, any IDE or Static Code Analyzer can sense the billion-dollar mistake, aka NullPointerException while writing the code to call the method.

Here are some best practices while defining a new Java method. 

• Method should have clear documentation with
• Purpose of the method
• Parameters of the method – Mark the parameter with @javax.annotation.Nonnull if null is not expected
• Return type of the method – Mark the return type with @javax.annotation.Nullable if it can be null

Example:

/** 

* This method filters product from the productList by supplied productId and type and return the same. 

* If no match found then returns null. 

* @param productId a non-null product ID for which the filter is requested

* @param type a non-null type value for which the filter is requested

* @return Product if found the match by productId and type else return null 

*/

public @Nullable Product filterProductByIdAndType(@Nonnull BigInteger productId, @Nonnull Character type) {
   Product product = null;
   for (Product eachProduct : productList) {
      if (productId.equals(eachProduct.getId()) && type.equals(eachProduct.getType())) {
         product = eachProduct;
         break;
      }
   }
   return product;
}

How it helps while calling the method?

It warns that the argument might be null while the method is expecting a Nonnull parameter.  In this case productId may be null because the assignment is conditional.




It also warns about the NPE because there is a possibility of getting Null from the method. In this case the method can return null as per the method documentation.

Let’s follow these best practices to avoid nightmares.