Overview
You work for an educational software company that is developing a suite of simple Physics simulations. The code in pendulum.zip is the beginning of a suite intended to permit the creation of a series of different types of pendulum simulation. You previously identified a code smell (“trivial layer”) in the AbstractEarthPendulum class, but figured it was mostly harmless. Now your team wants to be able to dynamically set which planet a pendulum is on during an interactive simulation, and to allow different kinds of gravity models that are impossible to represent with a single constant (e.g., latitude models).
Requirement
Run the main/test routine to see the expected behavior of the code.
Apply the refactoring approach “Collapse Hierarchy” to reduce the hierarchy levels by one. Ensure that the main/test routine still works as expected. Make a copy of all the code in a folder called “RefactoringStep1”
Next, use the Strategy design pattern (shown below) to replace the field g with a reference to a strategy object (as outlined below). This will allow different kinds of gravity models to be associated with a Pendulum instance dynamically.
Name the strategy interface GravityModel, with a single method
1 | public double getGravitationalField (); |
Assume that objects implementing GravityModel will be initialized with all state required to produce the gravitational field value under their specific model, and that this occurs before being assigned to a pendulum. In other words, the pendulums will just use the model assigned to it via the GravityModel interface. Adjust the pendulum constructors so that a GravityModel is assigned on initialization, and add a new method that will allow the GravityModel to be changed dynamically.
Define one concrete strategy called GravityConstant. This class simply receives a constant value for g in its constructor.
Run the main/test routine to ensure that the functionality hasn’t changed. Copy all the code into a folder called “RefactoringStep2”
Modify the provided main/test routine so that it initializes a SimplePendulum and a
RegularPendulum with a GravityConstant object, lets the pendulums swing for a little
while, then assigns a different GravityConstant object. For example, your first
GravityConstant could represent the Earth’s gravitational field (9.81 m/s^2), and the second
could represent Jupiter’s (25 m/s^2).