Assignment 4: Refactoring and Patterns
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).
1. Run the main/test routine to see the expected behavior of the code.
2. 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”
3. 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
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.
4. Run the main/test routine to ensure that the functionality hasn’t changed. Copy all the code into a

Patterns留学生作业代做、代做Collapse Hierarchy作业、代写c/c++，Python
folder called “RefactoringStep2”
5. 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).
Submit all code (including the 2 refactoring folders and the final version of the code with the
modified test) as a single zip file on Brightspace.
Marking Scheme for A4 (20 marks):
Rubric for A4 is not provided prior to the deadline.

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