Anonymous inner classes

Example 1

The following class uses an anonymous inner class:

package example

class InnerTest {

  static public function runme() {

    // Create instance of an anonymous inner class that derives from Object
    var counter = new Object() {

      // Anonymous inner classes can have variables (public, private, and so on)
      private var i = 0

      // Anonymous inner classes can have constructors
      construct() {
        print("Value is " + i + " at creation!")
      }

      // Anonymous inner classes can have methods
      public function incrementMe() {
        i = i + 1
        print("Value is " + i)
      }
    }

    // "counter" is a variable containing an instance of a class that has no name, 
    // but derives from Object and adds a private variable and a method

    counter.incrementMe()
    counter.incrementMe()
    counter.incrementMe()
    counter.incrementMe()
    counter.incrementMe()
  }
}

You can use the following code in the Gosu Scratchpad to test this class:

example.InnerTest.runme()

This code prints:

Value is 0 at creation!
Value is 1
Value is 2
Value is 3
Value is 4
Value is 5

Example 2

The following example demonstrates an advanced anonymous inner class. This anonymous inner class derives from a more functional class than Object. In this example, new inner class inherits the constructor and another method.

The following code defines a base class named Vehicle for the inner class:

package example

class Vehicle {
  construct() {
    print("A vehicle was just constructed!")
  }

  function actionOne(s : String) {
    print("actionOne was called with arg " + s)
  }
}

The following code creates a different class that uses Vehicle and defines an anonymous inner class that is based on Vehicle:

package example

class FancyVehicle {

  public function testInner() {

    // Create an inner anonymous class that extends Vehicle
    var test = new Vehicle() {
      public function actionTwo(s : String) {
        print("actionTwo was called with arg " + s)
      }
    }
    test.actionOne( "USA" )
    test.actionTwo( "ABCDEFG" )
  }
}

The inner class that defines the actionTwo method uses the new operator and not the class operator. The new operator defines a new class with no name and then creates one instance of that class.

Create the classes, and then try the following lines in Gosu Scratchpad to test the FancyVehicle class:

var g = new example.FancyVehicle()
g.testInner()

This code prints:

A vehicle was just constructed!
actionOne was called with arg USA
actionTwo was called with arg ABCDEFG