We know it’s all too common in Java to get a NullPointerException when we use an object reference which is null. This happens when our code tries to access a method or field of an object, or element of an array when there’s no instance present – e.g. it refers to null.
1 2 3 4 5 6 | class Animal { String name Animal parent}def animal = new Animal(name: "Bella") // no parent |
We might get an Animal instance from the outside and we need to get the name of the parent.
1 2 3 | def parentName = animal.parent.name// BLAM! java.lang.NullPointerException: // Cannot get property 'name' on null object |
Parent is null. Usually as a precaution we have to check for null beforehand.
1 2 3 | if (animal.parent != null) { def parentName = animal.parent.name} |
You can see that if we need the name of the grandparent, there are even more references which could be null.
1 | def grandParentName = animal.parent.parent.name |
We need a safe way to navigate through references we might expect to be null. Fortunately, with Groovy this is very easy. Use the Safe Navigation (or null-safe) operator which guards against NullPointerExceptions. This is just a question mark (?) before the dot (.)
animal?.name
A small little gem, but a great feature of Groovy.
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 | // instead of checking for nulls the Java wayif (animal.parent != null && animal.parent.parent != null) { def grandParentName = animal.parent.parent.name}// or using the Groovy truthif (animal.parent && animal.parent.parent) { def grandParentName = animal.parent.parent.name}// use safe navigationdef grandParentName = animal.parent?.parent?.name// and in combination with ElvisgrandParentName = animal.parent?.parent?.name ?: "Unknown" |
| Reference: | Avoid NullPointerException: Safe Navigation with Groovy from our JCG partner Ted Vinke at the Ted Vinke’s Blog blog. |
