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Understanding the Essence of Eiffel
Eiffel, named after the Eiffel Tower in Paris, is an object-oriented programming language known for its strong typing, design by contract methodology, and emphasis on software correctness. Developed by Bertrand Meyer in the late 1980s, Eiffel embodies the principles of simplicity, reliability, and reusability. Its unique features make it a powerful tool for building robust, maintainable software systems.
Mastering Eiffel: Sample Questions and Solutions
Question 1: Inheritance and Polymorphism
Consider the following Eiffel classes:
class
ANIMAL
create
make
feature
make is
-- Create an animal
do
-- Initialization code
end
speak is
-- Abstract feature to be implemented by subclasses
do
-- Default implementation
print ("Animal speaks.%N")
end
end
class
DOG
inherit
ANIMAL
feature
speak is
-- Dog barks
do
print ("Dog barks.%N")
end
end
Explain the concept of inheritance and polymorphism in Eiffel using the provided code snippet. How does the DOG class leverage inheritance to override the speak feature from its parent class ANIMAL?
Solution:
Inheritance in Eiffel allows a class to inherit features (methods) and properties from its parent class. In the given example, the DOG class inherits from the ANIMAL class using the inherit keyword. This means that DOG automatically gains access to all the features of ANIMAL, including the make and speak features.
Polymorphism, on the other hand, allows objects of different classes to be treated uniformly through a common interface. In Eiffel, polymorphism is achieved through dynamic binding. When a feature is called on an object, the Eiffel runtime system determines which version of the feature to execute based on the dynamic type of the object.
In the provided code, the speak feature is defined in both the ANIMAL and DOG classes. However, the DOG class overrides the speak feature inherited from ANIMAL by providing its own implementation. This is known as method overriding. When a speak feature is called on a DOG object, the Eiffel runtime system dynamically binds the call to the speak implementation in the DOG class, resulting in the output "Dog barks."
Question 2: Design by Contract
Explain the concept of Design by Contract (DbC) in Eiffel and its significance in software development. Provide an example demonstrating how DbC is implemented in Eiffel.
Solution:
Design by Contract (DbC) is a methodology introduced by Bertrand Meyer in Eiffel for building reliable and robust software systems. DbC revolves around the idea of specifying precise contracts between software components, where each component agrees to fulfill certain obligations (preconditions) before execution and promises to deliver certain results (postconditions) after execution.
In Eiffel, DbC is implemented using preconditions, postconditions, and class invariants. Preconditions specify conditions that must be true before a feature can be executed, while postconditions specify conditions that must be true after a feature has executed. Class invariants specify conditions that must be true for all instances of a class at all times.
class
STACK [G]
feature -- Access
push (item: G) is
-- Add an item to the top of the stack
require
not_full: not is_full
do
-- Add item to the top of the stack
ensure
item_added: item = top
end
pop is
-- Remove and return the item at the top of the stack
require
not_empty: not is_empty
do
-- Remove item from the top of the stack
ensure
item_removed: old top = item
end
top: G is
-- Retrieve the item at the top of the stack
require
not_empty: not is_empty
do
-- Return item at the top of the stack
end
feature -- Status
is_empty: BOOLEAN is
-- Check if the stack is empty
do
-- Return true if the stack is empty, false otherwise
end
is_full: BOOLEAN is
-- Check if the stack is full
do
-- Return true if the stack is full, false otherwise
end
invariant
capacity_non_negative: capacity = 0
count_non_negative: count = 0
count_not_exceed_capacity: count = capacity
In the above example, we have a generic stack implementation with preconditions, postconditions, and class invariants specified for its features. The push feature specifies a precondition not_full, ensuring that the stack is not full before adding an item. It also specifies a postcondition item_added, ensuring that the item added is indeed at the top of the stack after execution. Similarly, the pop feature specifies a precondition not_empty and a postcondition item_removed. Additionally, class invariants ensure that the capacity and count of the stack remain within valid bounds at all times.
Conclusion
Mastering Eiffel programming requires a deep understanding of its core concepts, including inheritance, polymorphism, and Design by Contract. By exploring sample questions and solutions like the ones provided above, you can enhance your proficiency and tackle even the most challenging assignments with confidence. So, the next time you find yourself struggling with Eiffel programming tasks, remember that ProgrammingHomeworkHelp.com is here to assist you every step of the way. Whether you need help understanding inheritance and polymorphism or implementing Design by Contract, our expert team is ready to write your Eiffel assignment and propel you towards success.
