CSCI 370 Lec 15: Object-Oriented Principles in ADTs, Project Guidelines, and the Memento Pattern

Tuesday, April 8

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Abstract Data Types and OOP Principles

Abstract Data Types (ADTs)

An Abstract Data Type (ADT) defines the logical behavior of a data structure without specifying how it is implemented. It is a conceptual blueprint that focuses on what operations are supported, not how they are performed. For example, a Stack ADT typically supports the following operations:

• push(item) – add item
• pop() – remove the top item
• peek() – look at the top item
• isEmpty() – check if the stack is empty

These operations are always expected from a stack, regardless of whether it is implemented via an array or linked list.

OOP Principles Demonstrated in ADTs

1. Encapsulation: The internal representation (e.g., array or linked list) is hidden. Only the interface (methods) is exposed.
2. Abstraction: The ADT focuses on what the structure does, not how.
3. Runtime Polymorphism: Different concrete implementations (like ArrayList and LinkedList) can be used through a common interface (List). This allows behavior to remain consistent while the underlying data structure varies.

Example:

List<String> list1 = new ArrayList<>();
List<String> list2 = new LinkedList<>();

Both lists support the same operations, demonstrating runtime polymorphism.

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Project Guidelines and Deliverables

Each student is assigned a design pattern (with the option to switch to a more challenging one). The final deliverable includes:

1. UML Diagram (10%)

• Can be sourced online and edited to match your implementation
• Should reflect your own class and interface names (e.g., StockMarket instead of Subject)
• Use class diagrams that identify interfaces and concrete implementations appropriately

2. Code Implementation (80%)

• Must follow Java coding conventions:
  • Class/type names: Start with uppercase
  • Variables and methods: Start with lowercase
• Should include at least three classes, each in a separate file unless using inner classes
• Students may use Replit to build and host the code, but it does not have to compile there—code should be compilable in local environments like IntelliJ or Eclipse
• Complexity is expected but flexible; there is no specific line count requirement as long as the project demonstrates the pattern clearly

3. Unit Tests (10%)

• Written using JUnit (e.g., assertTrue, assertFalse)
• Must test true/false conditions, not rely on manual output checking
• Tests should be automated and self-contained, not written inside main()

Example:

Assert.assertTrue(p.name.equals("FRED"));
Assert.assertFalse(p != null);  // expects p to be null

Unit tests must use assertions and not rely on output statements like System.out.println(), since tests may be run in headless environments.

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Java Builder Pattern Example Summary

A PersonBuilder class extends the Person class and allows construction using a step-by-step fluent interface.

Key Concepts:

• Mandatory fields are set via setImportantInfo()
• Optional fields are set via setOptionalInfo() and setCategoryAthruZ()
• validate() ensures that important fields are not blank
• The build() method returns a _Person object if validation passes, or null otherwise

Person p = pb.setImportantInfo("12888", "FRED")
             .setOptionalInfo(0, "")
             .setCategoryAthruZ("D")
             .build();

A failed validation returns null, which can be checked with assertions in unit testing.

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Memento Pattern (Java Implementation)

Motivation

The Memento Pattern is used to capture and restore an object’s state, enabling undo functionality. It is an application of the Single Responsibility Principle (SRP): keep history management separate from the object’s core functionality.

Before Refactoring (Without Memento)

The WordProcessor class stored its own history:

List<String> headerHistory = new ArrayList<>();
List<Font> fontHistory = new ArrayList<>();

This tightly coupled the history logic with the business logic and violates SRP by making one class manage both content and its history.

After Refactoring (Using Memento)

Three separate classes are used:

1. SnapshotOfDocument – holds a copy of the document state (header and font)
2. DocHistory – manages a stack of snapshots, with save() and get() methods for pushing and popping
3. WordProcessor2 – the refactored document class
   • Provides getMemento() and setMemento() methods
   • Only responsible for its current state, not history management

Main Program Demonstration

WordProcessor2 doc = new WordProcessor2();
DocHistory history = new DocHistory();
doc.setHeader("FRED");
history.save(doc.getMemento());
doc.setHeader("SAM");
System.out.println(doc.getHeader()); // Prints: SAM
doc.setMemento(history.get());
System.out.println(doc.getHeader()); // Prints: FRED

This allows history logic to be maintained independently of the WordProcessor’s internal logic, reducing the risk of bugs and improving modularity.

Benefits

• Cleaner code: WordProcessor2 has no internal logic for managing previous states
• SRP is upheld: DocHistory and SnapshotOfDocument take over the history-related responsibilities
• Easy to scale: More fields can be added to SnapshotOfDocument as needed, while keeping the WordProcessor2 class clean

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Types of Task Dependencies in Project Management

Dependencies define the order and relationship between tasks. There are four main types:

1. Finish to Start (FS)

   • Task B cannot start until Task A is finished
   • Example: Testing cannot begin until development is done

2. Start to Start (SS)

   • Task B cannot start until Task A has started
   • Example: You can’t record a tutorial until the coding process has begun

3. Finish to Finish (FF)

   • Task B cannot finish until Task A is finished
   • Example: Testing cannot be finalized until all code is finalized

4. Start to Finish (SF)

   • Task B cannot finish until Task A has started (less common)
   • Example: Cannot decommission an old server until a new one is up and running

These concepts are useful in project planning, especially in team environments, to prevent overlaps and ensure correct sequencing.

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Summary of Lecture 15 Topics

• Object-Oriented Principles applied in ADTs
• Clarified project structure and grading rubric
• Reviewed Builder Pattern implementation in Java
• Detailed Memento Pattern implementation with Java classes
• Covered software design principles like SRP
• Discussed how unit testing with JUnit should be structured
• Introduced types of task dependencies in software project workflows
• Mentioned upcoming design patterns to be covered: Iterator, Memento (completed), and Command

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