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Say you have a Groovy code like

Code Block

println 'hi'

As explained in Groovy Backstage, there is bytecode generated to achieve the
desired behaviour of printing to stdout.

The easiest way of looking at the generated bytecode is to groovyc your Groovy
source to a class file and process it with a Java Decompiler (e.g. JAD).
see See also: From source code to bytecode

The resulting code looks as follows (only the relevant snippet):

Code Block

Object aobj[] = { "hi" };
ScriptBytecodeAdapter.invokeMethod(this, "println", ((Object) (aobj)));


Invocation scheme

There is a delegation scheme like


Invoker calls invokeMethod(...) on the MetaClass of our class (with exceptions,
see below). It finds this MetaClass by looking it up in the MetaClassRegistry.
The Invoker holds a single instance of this registry.


MetaClass.invokeMethod(...) finally cares for the invokation, either by reflection or by dynamic bytecode generation.
Dynamic bytecode generation is supposed to be faster. For a class MyClass it generates
gjdk.groovy.lang.MyClass_GroovyReflector with an invoke method.

Does MyClass_GroovyReflector contain methods according to MyClass.groovy that can be called directly (question)

The cool thing about MetaClass is that you can dynamically add or remove methods to it.
One can even replace the whole MetaClass in the MetaClassRegistry. See ProxyMetaClass
for an example.

back to Groovy Backstage