Parameters Alice

Overview The need for more flexible methods Passing a parameter to a method Demos Using the Alice interface to write code for a parameter object

A beetle band Our task is to create an animation for a bug band as an advertisement for their next concert. In the animation, each band member will perform a short solo.

Storyboards Each bug band member will perform a solo. Do together Do in order georgeBeetle move up georgeBeetle move down play sound Do together Do in order ringoBeetle move up ringoBeetle move down play sound Do together Do in order paulBeetle move up paulBeetle move down play sound Do together Do in order lennonBeetle move up lennonBeetle move down play sound

Code for georgeBeetle solo This code will only work for georgeBeetle. Since each band member performs a solo, we will need four versions of the code.

A Better Solution Four versions of very similar code seems a bit tedious. The only things that change are the beetle and the music that plays. A better solution is to write a more flexible method.

Parameters Built-in methods provide flexibility by providing parameters such as distance and direction. Parameters allow you to pass in values (we call the values arguments). Example Parameters: distance, direction Arguments: 0.5 meters, 0.5 seconds

Kinds of Parameters Alice provides several kinds of parameters that can be used in your own methods.

The storyboard Solo: Parameters: bandMember, music Do together Do in order bandMember move up bandMember move down play music Back to our problem… We want to write only one method and use parameters to specify which band member is to perform and which music should be played.

Demo Demonstration of creating a method named solo that can be used for any band member. We will need an Object parameter -- which band member is to play a solo a Sound parameter -- which music should be played

World.solo with parameters.

Calling the solo method Note that in each call to the method, arguments must be given for both parameters.

A Number parameter Let's add a Number parameter to specify the height the bandMember jumps up and down.

Demo Demonstrate the use of a Number parameter to specify the height the bandMember is to jump

Assignment Read Chapter 4-2 Parameters Lab 4-2