![]() The most known immutable object in Java is String: once you have created a String, it remains the same until it is destroyed.īy default, Scala uses the immutable Set. The difference between mutable and immutable objects is that when an object is immutable, the object itself can’t be changed. There are two kinds of Sets, the immutable and the mutable one. The complete api of List object can be found here. In list4, the String “Hey!” is prepended to list3. List3 is a new list resulting of concatenating list1 and list2. List1 and list2 remain immutable, they didn’t change. Usually, the owner of an operation is the left operand, but in :: the owner is the right operand. This is because prepend an element at the beginning of a list is a constant-time operation, whereas append is a linear-time operation. Yes, you read it well: prepend (in Scala you can’t append elements to a list). The second one is the operator to prepend an element to a List. The first one is the operator for list concatenation. Maybe, the two main operators are ::: and. As in Strings, when you invoke any operation on a List, another List is created and returned when an operator is applied. But there are operators on Lists, so maybe you would be wondering why there are operators on Lists if they are immutable objects. That means that, once created, a Scala List can’t be modified. Lists in Scala are always immutable (in Java they can be mutable), they are designed to enable a functional style programming. Obviously, we can’t access a position of the Array with the operator, instead, the () operator is used. Companion classes will be explained in another post, but they can be seen as static classes or utility classes. Here there is another difference, we use the companion class to get an instance of Array. Var compactWay = Array(“I”,”like”,”this”,”way”)Īs it can be seen, there is no need to specify the type of the Array, the compiler will infer that the type is String. There is also another way to create and initialize an Array, which is less verbose and more compact. The other one is the way to instance the array, in Scala we use the () instead of. The way to specify the type of the Array is instead of. ![]() There are two important differences to notice. The first one is the classical way to create an object. In Scala, in contrast to Java, there is an Array object and it can be created in the same way as Java does. In this post we will try to explain four types of collections: Arrays, Lists, Sets and Maps. Note however, that since the backing array can't shrink or grow, operations such as List.add will throw UnsupportedOperationException.Despite all Scala code is translated to Java code, there are some differences between Scala Collections and Java Collections. If you write for instance final int arr = Īrrays. ![]() There's no way to make the elements of an array "final". There is however a simple workaround for the array case. This however works fine: List> sets = new ArrayList>() This won't compile: // Error: generic array creation Set sets = new Set You can't create an array of generic elements. we don't have to write list.add(new Integer(5)). So despite the fact that a List can only hold Integer values, we can still use list.add(5), i.e. See JEP 218: Generics over Primitive Types.)Īutoboxing: Luckily there's something called autoboxing which silently transforms an int to an Integer behind the scenes. (Support for this is under way and might be available in something like Java 13. You can have a List of integers, but you'll have to use List. ![]() add( 5, 17) // insert 17 at index 5 PrimitivesĪn arrray can store primitive values. Lists however, also allows you to insert an element in the middle, shifting all subsequent elements from index i to i + 1. Insertionīoth arrays and lists allow you to update the content at a specific index. Most list types (including ArrayList) provide List.add and List.remove which allows it to grow and shrink. You can for instance not append an element to the end of an array, or remove an element. Once you've created an array, it can't be resized. Unless you have a specific reason to use an array (such as those mentioned above), use a List, such as an ArrayList. You need to work with primitives for performance reasons.An API method takes an array as argument or returns an array.Java: Arrays vs ArrayLists (and other Lists)Īn array (something like int) is a built in type while ArrayList is a regular class part of the Java standard library. ![]()
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