{"id":1112,"date":"2020-07-02T11:06:48","date_gmt":"2020-07-02T09:06:48","guid":{"rendered":"https:\/\/www.loicmathieu.fr\/wordpress\/?p=1112"},"modified":"2020-07-02T11:06:48","modified_gmt":"2020-07-02T09:06:48","slug":"java-15-quoi-de-neuf","status":"publish","type":"post","link":"https:\/\/www.loicmathieu.fr\/wordpress\/informatique\/java-15-quoi-de-neuf\/","title":{"rendered":"Java 15 : what’s new ?"},"content":{"rendered":"

Now that Java 15 is features complete (Rampdown Phase One at the day of writing), it\u2019s time to walk throught all it\u2019s functionalities that brings to us, developers, this new version.<\/p>\n

This article is part of a series on what\u2019s new on the last versions of Java, for those who wants to read the others, here are the links : Java 14<\/a>, Java 13<\/a>, Java 12<\/a>, Java 11<\/a>,\u00a0Java 10,<\/a>\u00a0and\u00a0Java 9<\/a>.<\/p>\n

This new version brings lots of new JEPs, the main one being the addition of Sealed Classes. Records and Pattern Matching introduced in Java 14 remain in preview in this version.<\/p>\n

JEP 360 : Sealed Classes<\/h2>\n

Sealed Classes allow you to limit the number of implementations of a class or an interface to a predefined list. The hierarchy of this class \/ interface is therefore closed (sealed).<\/p>\n

As this hierarchy is known at compile time, this opens up possibilities for Pattern Matching, a future implementation of switch based on the type of an object is planned in one of the next versions of Java. This also allows the author of a class \/ interface to express its use in a finer way than via visibility modifiers by restricting its use to a specific list.<\/p>\n

Here are some examples taken from the JEP<\/p>\n

package com.example.geometry;\n\npublic sealed class Shape\n    permits Circle, Rectangle, Square {...}\n<\/code><\/pre>\n
If classes are declared in the same source file, the permits<\/code> clause can be ignored.<\/p>\n
package com.example.geometry;\n\nsealed class Shape {...}\n    class Circle    extends Shape {...}\n    class Rectangle extends Shape {...}\n    class Square    extends Shape {...}\n<\/code><\/pre>\n
Now that we know the list of classes implementing an interface, we can more easily write a series of if\/else on the Shape<\/code> class:<\/p>\n
Shape rotate(Shape shape, double angle) {\n    if (shape instanceof Circle) return shape;\n    else if (shape instanceof Rectangle) return shape.rotate(angle);\n    else if (shape instanceof Square) return shape.rotate(angle);\n}\n<\/code><\/pre>\n
When Pattern Matching would have been extended to cover Sealed Classes, we could write a switch with a test on the type of an object:<\/p>\n
Shape rotate(Shape shape, double angle) {\n    return switch (shape) {\/\/ won't compile in Java 15 ...\n        case Circle c    -> c;  \/\/ no action needed\n        case Rectangle r -> r.rotate(angle);\n        case Square s    -> s.rotate(angle);\n    }\n}\n<\/code><\/pre>\n
A new keyword has been introduced non-sealed<\/code> which opens the hierarchy from one of the subclasses or subinterfaces of a sealed class.<\/p>\n
Other news<\/h2>\n