Groovy for Domain-specific Languages - Second Edition

Groovy Closures

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In the preceding code, we implemented a simple closure, which accepts a single
string parameter. We can now make use of this closure within our Groovy code,
as follows:

given: "an instance of a Java Closure"

def stringParams = new StringClosure(this)

when: "Invoking this with the parameters defined by the doCall"

stringParams "String"

then: "we expect them to work"

notThrown Exception

when: "we pass an incorrect type for the doCall parameter"

stringParams 1

then: "we expect that Groovy won't find a matching Closure"

thrown MissingMethodException

Now, we can try a more complex closure that accepts multiple different parameter
types by implementing multiple doCall methods in the closure:

public class MultiClosure extends Closure{

public MultiClosure(Object owner) {

super(owner);

}

public MultiClosure(Object owner, Object thisObject) {

super(owner, thisObject);

}

Object doCall(String message) {

System.out.println(message);

return null;

}

Object doCall(Integer number) {

System.out.println(number);

return null;

}

}

We can then pass the different parameter types to this closure, and it will work fine:

given: "an instance of a Java Closure"

def multiParams = new MultiClosure(this)

when: "Invoking these with the parameters defined by the doCall"

multiParams "String"

then: "we expect them to work"

notThrown Exception

when: "Invoking these with the parameters defined by the doCall"

multiParams 1

then: "we expect them to work"

notThrown Exception

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