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Using ExpandoMetaClass to add behaviour

Groovy includes a special MetaClass called an ExpandoMetaClass that allows you to dynamically add methods, constructors, properties and static methods using a neat closure syntax.

How does it work? Every java.lang.Class is supplied with a special "metaClass" property that will give you a reference to an ExpandoMetaClass instance.

For example to obtain the ExpandoMetaClass of the java.lang.String class you use:

This adds a method called swapCase to the String class.

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By default ExpandoMetaClass doesn't do inheritance. To enable this you must call ExpandoMetaClass.enableGlobally() before your app starts such as in the main method or servlet bootstrap

Further Reading:

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