class Examples, trait
This page was last reviewed on Dec 19, 2023.
Dot Net Perls
Classes. In Scala 3.3 programs we use classes. A Game class has fields and methods—it has the current score and players. And it can take turns with a play method.
With traits, and the trait keyword, we can extend features of our classes. A Game might be extended to adjust the rules. It might add features or options.
First example. Here we introduce a Test class. On this class we find a method print(). This writes a greeting to the screen. We create a new instance of Test with the new-keyword.
class Test { def print() = { // Print a greeting. println("Hello") } } object Program { def main(args: Array[String]): Unit = { // Create new instance of Test class. val t = new Test() t.print() } }
Traits. A trait is used to extend a class. We can compose a class by adding those traits to its definition. This allows us to combine many capabilities in a class.
Here We have a Page class, and an Image and Paragraphs traits. A trait is defined in a similar way as a class, but uses the trait keyword.
Next The Page class is based on the Page class, but also adds the Image and Paragraphs traits. It contains all 3 methods.
Finally We create a ComplexPage instance and call print, printImages and printParagraphs from the Page class and the two traits.
class Page { def print() = { println("Page") } } trait Image { def printImages() = { // Print images. println("Images") } } trait Paragraphs { def printParagraphs() = { // Print paragraphs. println("Paragraphs") } } // Extend Page. // ... Add Image and Paragraphs traits. class ComplexPage extends Page with Image with Paragraphs { } object Program { def main(args: Array[String]): Unit = { // Create ComplexPage instance. // ... Use Page, Image, Paragraphs methods on it. val example = new ComplexPage() example.print() example.printImages() example.printParagraphs() } }
Page Images Paragraphs
Review. Scala provides both functional and object-oriented features. With classes and traits we compose complex models. This is streamlined but conceptually similar to Java.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Dec 19, 2023 (edit link).
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