Implicit Conversions with Identity Functions

Posted by & filed under Java.

What use is a method that just returns its input? Surprisingly useful. A surprising use is as a way to convert between types. There’s a well known trick that’s often used to work around Java’s terrible array literals that you may have come across. If you have a method that takes an array as an… Read more »

Builder Pattern with Java 8 Lambdas

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The builder patten is often used to construct objects with many properties. It makes it easier to read initialisations by having parameters named at the callsite, while helping you only allow the construction of valid objects. Builder implementations tend to either rely on the constructed object being mutable, and setting fields as you go, or… Read more »

Frameworkless Dependency Injection

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Twice recently we have had “fun” trying to get things using HK2 (Jersey), to place nicely with code built using Guice and Spring. This has renewed my appreciation for code written without DI frameworks. The problem with (many) DI frameworks. People like to complain about Spring. It’s an easy target, but often the argument is… Read more »

Deep Pattern Matching in Java

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This is a follow up to Pattern matching in Java, where I demonstrated pattern matching on type and structure using Java 8 features. The first thing most people asked is “does it support matching on nested structures?” The previous approach did not, at least not without creating excessive boilerplate constructors. So here’s another approach that… Read more »

Tuples in Java

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The absence of tuples in Java is often bemoaned. Tuples are collections of a variety of types. They might look like (“benji”,8,”weber”) – a 3-tuple of a string, a number, and another string. People often wish to use tuples to return more than one value from a method. Often this is a smell that we… Read more »

JSON to Java Interfaces with Nashorn

Posted by & filed under Java, JavaScript.

Here’s a neat trick to transform JSON into Java objects that implement an interface with the same structure. Java 8 comes with Nashorn – a JavaScript runtime that has a number of extensions. One of these extensions allows you to pass a JavaScript object to a constructor of an interface to anonymously implement that interface…. Read more »

Pattern Matching in Java

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One of the language features many people miss in Java is pattern matching, and/or an equivalent of Scala case classes. In Scala we can match on types and structure. We have “switch” in Java, but it’s much less powerful and it can’t even be used as an expression. It’s possible to simulate matching in Java… Read more »

Java Value Objects

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Java 8 not only gives us both default and static methods on interfaces. One of the consequences of this is you can create simple value objects using interfaces alone, without the need to define a class. Here’s an example. We define a Paint type which is composed of an amount of red/green/blue paint. We can… Read more »

Java Forwarding-Interface Pattern

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Java 8’s default methods on interfaces means we can implement the decorator pattern much less verbosely. The decorator pattern allows us to add behaviour to an object without using inheritance. I often find myself using it to “extend” third party interfaces with useful additional behaviour. Let’s say we wanted to add a map method to… Read more »

Joins in pure-java database queries

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I’ve been thinking about how to express joins in my pure Java query library. Hibernate and other ORMs allow you to map collection fields via join tables. They will take care of cascading inserts and deletes from multiple tables for you. While this is nice and easy, it can to cause problems with bigger object… Read more »