Unlike Java’s Optional, which is a library feature, JPlus provides null-safety at the language level. It allows developers to write code where null-safety is enforced consistently, without wrapping every value in an Optional. In that sense, JPlus brings the same kind of safety and clarity that Kotlin offers but keeps full compatibility with Java syntax and tooling.

This is exactly the core problem that JPlus aims to solve.

The C Preprocessor also does all of those things. That’s expected of a preprocessor. If you say “you can write java code with a bit of extra sugar and JPlus turns it back into ‘regular’ java,” then that’s a preprocessor.

A simple preprocessor only performs code transformation and cannot analyze the meaning of the code or ensure type safety. However, JPlus goes beyond mere transformation by providing static analysis capabilities, such as generating a parse tree and checking nullability. It also includes functionality to automatically generate necessary Java code through the apply syntax. As a result, the combination of performing nullability static analysis and generating code via apply cannot be expressed or handled using any existing Java syntax alone.

JPlus follows standard Java syntax while aiming to be an “Upgraded Java” by adding features that Java developers consider practically useful in real-world projects. This allows existing Java developers to utilize new features with minimal learning curve. All features are added on top of Java syntax. For example, null-safety syntax (type?, ?.) and boilerplate code generation syntax (apply). As a result, developers can experience an enhanced version of Java while continuing to use existing Java code and libraries without modification. This should clarify exactly where JPlus fits in the ecosystem.

You can probably adopt both for a large existing project. Old files get compiled with JPlus, new files will be written in Kotlin. Old files can also gradually be ported to kotlin.

Exactly, that could work. You can keep the existing files as they are and compile them with JPlus, while writing new modules in Kotlin to adopt it gradually. JPlus can serve as a stepping stone before moving fully to Kotlin. However, converting all Java code in an existing project to Kotlin would not only carry significant risks but also be costly. With JPlus, you can fully leverage the proven existing Java codes.

Groovy doesn’t have null safety or boilerplate code generation features. That’s why JPlus was created to address what Java developers truly feel is missing. Go post that comment in the Groovy community.

As the title suggests, this page is an introduction to the project, while the other posts focus on how to use it.

Things can get confusing if the explanation is too long, so here’s a concise way to put it.

It’s not entirely clear whether Groovy includes 100% of Java syntax, but in my view, Groovy focuses on enhancing the language itself, addressing areas where it falls short compared to modern languages.

On the other hand, JPlus is similar to how TypeScript addresses JavaScript’s lack of type safety: it focuses on strengthening Java’s safety while improving developer convenience through features like boilerplate code generation. Importantly, JPlus code always compiles down to standard Java, which means it can be integrated seamlessly into existing Java projects without changing the build environment or toolchain.

In short:

Groovy: Focuses on enhancing the expressive power of Java, adding modern language features and syntactic flexibility.

JPlus: Focuses on enhancing language safety and developer convenience, while maintaining full compatibility with Java. This allows developers to adopt JPlus without worrying about breaking existing Java projects.

From Wikipedia:

In computer science, a preprocessor (or precompiler)[1] is a program that processes its input data to produce output that is used as input in another program. […], which is often used by some subsequent programs like compilers.

The emphasis is mine.

Both Typescript and SASS are examples of preprocessors.

By that logic, the C compiler would also be a preprocessor since it converts C code into assembly. Simply calling something a preprocessor just because its output is source code is not logically correct. The same applies to JPlus: the fact that it ultimately produces Java source code does not make it a preprocessor. Internally, it performs compiler-level processes such as AST generation, null-safety checks, and boilerplate code generation, so it should be regarded as a proper compiler.

Kotlin is great for null-safety, but Kotlin isn’t a superset, you can’t just compile a java file with kotlin and have it work.

JPlus allows you to enforce null-safety without rewriting your existing Java code, which can be easier for teams working in legacy projects or who prefer staying in pure Java.

Kotlin isn’t a superset, you can’t just compile a java file with kotlin and have it work afaik. That seems to be the point here.

This is more like a preprocessor anyway, like SASS to CSS. The compiler spits out Java source code, not jvm bytecode.

Exactly, as you said, Kotlin isn’t a Java superset. you can’t just compile a Java file with Kotlin and have it work. JPlus works similarly in that it outputs standard Java source code rather than JVM bytecode.

However, JPlus is not merely a “preprocessor.” It actually parses Java source like a compiler, performs null-safety checks and boilerplate code generation on the generated parse tree, and finally produces standard Java code. In that sense, JPlus should be considered a compiler. The only difference is that its output is Java code; if the code generation step were extended to produce JVM bytecode directly, it could bypass the Java source entirely and generate bytecode straightaway.

The key point is that, just like TypeScript addresses JavaScript’s lack of type safety, JPlus fills in some of Java’s gaps. It allows you to keep almost all of your existing Java code while adding features like null-safety and automatic boilerplate generation, improving both safety and developer convenience.

There’s Groovy. Their examples use a bit different syntax, like a lack of semicolons, and Gradle might also give the wrong idea. But it’s fully compatible with Java source code iirc, just adds its own stuff on top and broadens the allowed syntax a bit.

Groovy is highly compatible with Java and most Java code runs in Groovy without changes. However, it’s not 100% identical. Groovy introduces dynamic typing, additional syntax, and runtime behaviors that can differ from Java. JPlus, on the other hand, aims to keep Java syntax almost intact while adding null-safety and boilerplate code generation making it easier to apply to existing Java projects without rewriting code