Groovy matching constructor error

February 19, 2021

If you encounter an exception like this:

groovy.lang.GroovyRuntimeException: Could not find matching constructor for: com.example.BaseClass$InnerClass(...)
        at YourClass.yourMethod(YourClass.groovy:20)

One of possible problems may be that there is a class InnerClass, which is declared inside BaseClass:

class BaseClass {
  class InnerClass {
    InnerClass(/*...*/) {
      // Your constructor
    }
  }
}

And in some other class (even inherited from BaseClass) you are trying to instantiate InnerClass:

class YourClass extends BaseClass {
  def yourMethod() {
    InnerClass inner = new InnerClass(/*...*/)
  }
}

Then you will get groovy.lang.GroovyRuntimeException: Could not find matching constructor. The point is that objects of inner classes in groovy need to be created using a method in the wrapper class.

Let’s add the corresponding method to BaseClass:

class BaseClass {
  def createInnerClass(/*...*/) {
    return new InnerClass(/*...*/)
  }

  class InnerClass {
    InnerClass(/*...*/) {
      // Your constructor
    }
  }
}

And in YourClass we use the newly created createInnerClass() method:

class YourClass extends BaseClass {
  def yourMethod() {
    InnerClass inner = createInnerClass(/*...*/)
  }
}

After that, the exception will disappear.