"instantiating" a List in Java?

java

interface-vs-class

list-implementation

polymorphism

byNikita Barsukov·Jan 25, 2025

In Java, choose ArrayList or LinkedList to instantiate a List. Here's a code snippet for initializing an ArrayList:

List<String> list = new ArrayList<>();

In the example above, we've habituated a List of Strings. Java's diamond operator lets you keep it short and neat.

Interface vs Class

In Java's type system, "List" is an interface, not a concrete class. Attempting to instantiate an interface is a no-go, as an interface is akin to a contract that classes sign agreeing to provide certain methods.

Implementations: ArrayList vs LinkedList

Two popular implementations of the List interface are ArrayList and LinkedList. Choose according to your needs - ArrayList shines in lookup scenarios; LinkedList excels during insertions and deletions.

Custom Implementation: Not Always Required

Creating a custom implementation of the List interface can be thrilling, but it's not always the game-changer. The off-the-shelf ones like ArrayList and LinkedList are adept at handling most use cases.

LinkedList: The Insert/Delete Maven

When your application involves frequent insertions and deletions, particularly in the middle of the List, LinkedList works like a charm.

ArrayList: The Random Access Maestro

When you need fast access to elements by their indices, Duke's choice is ArrayList - it can fetch any element in constant time.

When you try the impossible

Are you trying to instantiate a List interface directly and getting the error "java.util.List is abstract; cannot be instantiated"? Remind yourself in Java, Interfaces are for inspiration, classes are for implementation.

Glad you asked about Upcasting

Creating an ArrayList instance and assigning it to a List reference is a brilliant way of keeping your options open. Flexibility thy name is upcasting!

Polymorphism in Play

With upcasting, you can switch between ArrayList and LinkedList without breaking a sweat - that's the charm of polymorphism. High five to the principle of coding to an interface, not an implementation!💡

Java vs. .NET: Lists Explored

In the .NET world, you can instantiate a list directly. But Java prefers you to make an informed decision, choosing either ArrayList or LinkedList, depending on your use case.