55. Rewriting equals() via type patterns for instanceof It is not mandatory to rely on instanceof for implementing the equals() method, but it is a convenient approach to write something as follows: public class MyPoint { private final int x; private final int y; private final int z; public MyPoint(int x, int y, int z) […]
Tackling type patterns for instanceof and streams – Objects, Immutability, Switch Expressions, and Pattern Matching
57. Tackling type patterns for instanceof and streams Let’s consider a List<Engine> where Engine is an interface implemented by several classes such as HypersonicEngine, HighSpeedEngine, and RegularEngine. Our goal is to filter this List and eliminate all RegularEngine that are electric and cannot pass our autonomy test. So, we can write a code as follows: […]
Adding guarded pattern labels in switch – Objects, Immutability, Switch Expressions, and Pattern Matching
59. Adding guarded pattern labels in switch Do you remember that type patterns for instanceof can be refined with extra boolean checks applied to the binding variables to obtain fine-grained use cases? Well, we can do the same for the switch expressions that use pattern labels. The result is named guarded pattern labels. Let’s consider […]
Dealing with pattern labels dominance in switch 2 – Objects, Immutability, Switch Expressions, and Pattern Matching
The order of pattern labels is imposed by the class hierarchy and is quite strict, but we can do some changes without creating any dominance issues. For instance, since Extra and Large are subclasses of Medium, we can switch their positions. Some things apply to Jumbo and Huge since they are both subclasses of Medium […]
Dealing with pattern labels dominance in switch – Objects, Immutability, Switch Expressions, and Pattern Matching
60. Dealing with pattern labels dominance in switch The compiler matches the selector expression against the available pattern labels by testing the selector expression against each label starting from top to bottom (or, from the first to the last) in the exact order that we wrote them in the switch block. This means that the […]
Dealing with completeness (type coverage) in pattern labels for switch 2 – Objects, Immutability, Switch Expressions, and Pattern Matching
Now, the selector expression can be any type which means that the total pattern Vehicle v is not total anymore. While Vehicle v becomes an optional ordinary pattern, the new total pattern is case Object obj. This means that we can cover all possible values by adding the default label or the case Object obj […]
Dealing with completeness (type coverage) in pattern labels for switch – Objects, Immutability, Switch Expressions, and Pattern Matching
61. Dealing with completeness (type coverage) in pattern labels for switch In a nutshell, switch expressions and switch statements that use null and/or pattern labels should be exhaustive. In other words, we must cover with explicit switch case labels all the possible values. Let’s consider the following example: class Vehicle {}class Car extends Vehicle {}class […]
Dealing with completeness (type coverage) in pattern labels for switch 3 – Objects, Immutability, Switch Expressions, and Pattern Matching
This code compiles! There is no default label and no total pattern but the switch expression covers all possible values. How so?! This interface is declared as sealed via the sealed modifier: public sealed interface ClassDescextends ConstantDesc, TypeDescriptor.OfField<ClassDesc> Sealed interfaces/classes were introduced in JDK 17 (JEP 409) and we will cover this topic in chapter […]
Understanding the unconditional patterns and nulls in switch expressions – Objects, Immutability, Switch Expressions, and Pattern Matching
62. Understanding the unconditional patterns and nulls in switch expressions Let’s imagine that we use JDK 17 and we have the following code: private static String drive(Vehicle v) { return switch (v) { case Truck truck -> “truck: ” + truck; case Van van -> “van: ” + van; case Vehicle vehicle -> “vehicle: ” […]
Defining a day period – Working with Date and Time
63. Defining a day period Let’s imagine that we want to say hello to a friend from another country (different time zone) via a message such as Good morning, Good afternoon, and so on based on his local time. So, having access to AM/PM flags is not enough, because we consider that a day (24 […]