Groovy Metaprogramming

Groovy metaprogramming tutorials. Runtime and compile-time techniques including MetaClass, ExpandoMetaClass, categories, mixins, and AST transforms.

Groovy ExpandoMetaClass – Add Methods at Runtime with 10+ Examples

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Groovy ExpandoMetaClass lets you add instance methods, static methods, constructors, and operators to any class at runtime. 10+ tested examples included. “ExpandoMetaClass is Groovy’s answer to open classes. If you wish a Java class had a method, just add it.” Guillaume Laforge, Groovy Project Lead Last Updated: March 2026 | Tested on: Groovy 5.x, Java 17+ | Difficulty: Intermediate to Advanced | Reading Time: 18 minutes Ever wished String had a method to check for palindromes, or that Integer could ... Read More

Groovy MOP (Meta-Object Protocol) – How It Works with 10+ Examples

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Groovy MOP (Meta-Object Protocol) explained with 10+ tested examples. Learn method resolution, MetaClass hierarchy, and how Groovy dispatches every call. “The MOP is the beating heart of Groovy’s dynamism. Every method call, every property access, every operator – they all flow through the Meta-Object Protocol.” Dierk König, Groovy in Action Last Updated: March 2026 | Tested on: Groovy 5.x, Java 17+ | Difficulty: Intermediate to Advanced | Reading Time: 18 minutes Unlike Java, where method calls are resolved at compile ... Read More

Groovy Categories and Mixins – Extend Existing Classes with 10+ Examples

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Learn Groovy categories and mixins with 10+ tested examples. Add scoped methods to classes, compose behaviors, and extend JDK classes safely. “Categories let you try on new methods like clothes – wear them when you need them, take them off when you’re done.” Dave Thomas, The Pragmatic Programmer Last Updated: March 2026 | Tested on: Groovy 5.x, Java 17+ | Difficulty: Intermediate | Reading Time: 18 minutes Adding methods globally with ExpandoMetaClass is powerful but permanent (until cleanup). What if ... Read More