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Thursday, March 4, 2010

Groovy Goodness: Invoke Methods Dynamically

In Groovy we can invoke a method just like in Java: we simply type the name of the method in our code. But what if we want to invoke a method name, but we don't know the name yet when we write the code, but we do know it at runtime? We can use the Reflection API for example to invoke the method, but in Groovy it can be shorter. In Groovy we can use a variable value for method invocation with a GString. The GString is evaluated at runtime and the result must be the method name we want to invoke.

class Simple {
    def hello(value) {
        "Hello $value, how are you?"
    }
    
    def goodbye() {
        "Have a nice trip."
    }
}

def s = new Simple()
def methods = ['hello', 'goodbye']

assert 'Hello mrhaki, how are you?', s."$methods[0]"('mrhaki')
assert 'Have a nice trip.', s."$methods[1]"

5 comments:

Anonymous said...

Good to see you are posting again - I've missed your daily tidbits of Groovy!

mrhaki said...

Hi, thanks. I will be posting more regularly from now on. Probably each workday.

jquery said...

It was interesting to read this article and I hope to read a new article about this subject in your site in the near time.

Ravi Shekhar said...

Can we instantiate an object of a class if we have the class's name in String?

Hubert Klein Ikkink said...

@Ravi Shekhar: You can via a little detour. You must first convert the String value to a Class using as Class. Then you can invoke newInstance() method to invoke the constructor. See the following example:
def i = 'java.lang.Integer' as Class
assert i.newInstance(42) == 42I

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