How to sort a list of objects and keep null objects at the end

We have already seen how to sort a list based on a specified parameter using a comparator. However, so far, we have worked with lists having non-null values. In this recipe, we will see how to sort a list of objects, which have the null property (on which we are sorting). So let's get started.

Getting ready

I'll be using IntelliJ IDEA for writing and running Kotlin code; you are free to use any IDE that can do the same task.

How to do it…

Now, let's follow these steps to sort a list, while keeping null objects at the end:

1. Let's create a Person class having an age property that can be null:

class Person(var age:Int?)

2. Now, let's create a list of Person objects:

val listOfPersons=listOf(Person(10), Person(20), Person(2), Person(null))

3. Finally, we want to sort them in ascending order, while keeping the null items at the end:

val sortedList=listOfPersons.sortedWith(compareBy(nullsLast<Int>(),{it.age}))
sortedList.forEach {
    print(...