jelvis

jelvis is an elvis operator for Java 8 & Scala. jelvis eats NullPointerException in chained calls and returns null instead.

For example in this chained call:

person.getAddress().getCountry()

you can get at least two NPEs: first when person is null and second when getAddress() returns null.

jelvis takes care of NPEs for you. For the above call jelvis will return the value of getCountry() or null if either person or getAddress() is null. No NPE will be thrown.

Getting started

Java 8

All you need is just one static import:

import static com.github.lukaszbudnik.jelvis.Elvis.elvis;
//...
Person person = new Person();
// old syntax requires 2 arguments
// the first argument to `elvis` method is the root object
// the second one is the lambda function to be evaluated
String isoCode = elvis(person, p -> p.getAddress().getCountry().getISOCode());

// new syntax takes just a lambda to be evaluated
// a little bit shorter than the old syntax.
String isoCode = elvis(() -> person.getAddress().getCountry().getISOCode());

No NullPointerException is thrown. All other exceptions are preserved. Java 8 lambdas have some problems with functions throwing checked exceptions (code simply does not compile). To overcome this limitation jelvis is wrapping all checked exceptions into a runtime exception: ElvisException.

Prior to jelvis 1.3 you had to explicitly wrap functions throwing exceptions using Elvis.wrappedFunction(). This is now done automatically:

import static com.github.lukaszbudnik.jelvis.Elvis.elvis;
//...
Person person = new Person();
// starting with jelvis 1.3 there is no need to use Elvis.wrappedFunction()
// old syntax
String line2 = elvis(person, p -> p.getAddress().getLine2());
// new syntax
String line2 = elvis(() -> person.getAddress().getLine2());

Scala

There is an implicit converter which converts Scala Function1 into jelvis functions. So in case of Scala you have to add two imports:

import com.github.lukaszbudnik.jelvis.Elvis._
import com.github.lukaszbudnik.jelvis.ElvisScalaToJavaConverters._

And then just use the elvis method in your code:

val person = new Person
// old syntax
val isoCode = elvis(person, (p: Person) => p.getAddress.getCountry.getISOCode)
// new syntax
val isoCode = elvis(() => person.getAddress.getCountry.getISOCode)

Exceptions? In Scala all exceptions are unchecked. You don't have to worry about them at all. For example p.getAddress.getLine2 doesn't have to be wrapped using Elvis.wrappedFunction(). Thus, when running from Scala, you will never see ElvisException. The call simply looks like this:

elvis(person, (p: Person) => p.getAddress.getLine2)

See examples for more information.

Examples

See src/test/java for Java unit tests and src/test/scala for Scala ones.

Download

Use the following Maven dependency:

<dependency>
  <groupId>com.github.lukaszbudnik.jelvis</groupId>
  <artifactId>jelvis</artifactId>
  <version>{version}</version>
</dependency>

or open search.maven.org and copy and paste dependency id for your favourite dependency management tool (Gradle (jelvis uses Gradle), Buildr, Ivy, sbt, Leiningen, etc).

License

Copyright 2015 Łukasz Budnik

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.