What kind of List does Collectors.toList() return?

by

So, what concrete type (subclass) of List is being used here? Are there any guarantees?

If you look at the documentation of Collectors#toList(), it states that – “There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned”. If you want a particular implementation to be returned, you can use Collectors#toCollection(Supplier) instead.

Supplier<List<Shape>> supplier = () -> new LinkedList<Shape>();

List<Shape> blue = shapes.stream()
            .filter(s -> s.getColor() == BLUE)
            .collect(Collectors.toCollection(supplier));

And from the lambda, you can return whatever implementation you want of List<Shape>.

Update:

Or, you can even use method reference:

List<Shape> blue = shapes.stream()
            .filter(s -> s.getColor() == BLUE)
            .collect(Collectors.toCollection(LinkedList::new));

More Related Contents:

  1. Splitting List into sublists along elements
  2. Java 8 Collectors.toMap SortedMap
  3. Java 8 grouping using custom collector?
  4. Java 8 List into Map
  5. Comparator.reversed() does not compile using lambda
  6. Java 8: Lambda-Streams, Filter by Method with Exception
  7. What is the breakdown for Java’s lambda syntax?
  8. LambdaConversionException with generics: JVM bug?
  9. Java 8 method reference unhandled exception
  10. How do I define a method which takes a lambda as a parameter in Java 8?
  11. Lambda expression and method overloading doubts
  12. Java 8 chained method reference?
  13. Why are Java 8 lambdas invoked using invokedynamic?
  14. Why do Consumers accept lambdas with statement bodies but not expression bodies?
  15. How to dynamically do filtering in Java 8?
  16. Why can’t I throw an exception in a Java 8 lambda expression? [duplicate]
  17. Do lambda expressions have any use other than saving lines of code?
  18. Java 8 Supplier with arguments in the constructor
  19. What is a Java 8 Lambda Expression Compiled to? [duplicate]
  20. Java idiom for lambdas with non-SAM interfaces
  21. Local variable log defined in an enclosing scope must be final or effectively final
  22. Java access bean methods with LambdaMetafactory
  23. Proper usage of Optional.ifPresent()
  24. java: Arrays.sort() with lambda expression
  25. Picking elements of a list until condition is met with Java 8 Lambdas
  26. Why does this Java 8 lambda fail to compile?
  27. FunctionalInterface Comparator has 2 abstract methods
  28. How to apply Filtering on groupBy in java streams
  29. Stream.peek() method in Java 8 vs Java 9
  30. Java 8 stream map to list of keys sorted by values

Leave a Comment