Java Generics 2 — Advanced Assignment

🎯 Objective

Enhance your understanding of Java Generics by implementing and utilizing more complex generic structures, including multi-type generics, collections, wildcards, and practical caching.

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🧩 Project Overview

This project demonstrates:

• Multi-type generic classes (Pair<K, V>)
• Generic data structures (Stack<T>)
• Generic methods and wildcards (sort, printCollection, sumOfNumberList)
• Complex generic implementations (Cache<T> with bounded wildcards)
• Custom class implementing Comparable<T> (Student)

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🗂️ Project Structure

Generic2/
├─ src/
│  └─ main/
│     └─ java/
│        └─ genericsadvanced/
│           ├─ Pair.java
│           ├─ Stack.java
│           ├─ CollectionsUtil.java
│           ├─ Cache.java
│           ├─ Student.java
│           └─ Main.java
└─ README.md

Each file uses the package declaration:

package genericsadvanced;

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⚙️ How to Compile and Run

✅ Step 1: Compile

Open your terminal (PowerShell or CMD) in the project root:

javac -d out src\main\java\genericsadvanced\*.java

✅ Step 2: Run

java -cp out genericsadvanced.Main

If using VS Code, you can press Run ▶️ on Main.java.

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🧱 Part 1: Implementing Complex Data Structures

🔹 Pair<K, V>

• Stores a key-value pair of any types.

• Methods: getKey(), getValue(), setKey(), setValue().

• Example:

  Pair<String, Integer> personAge = new Pair<>("Age", 30);
  System.out.println(personAge); // Pair{Age = 30}

🔹 Stack<T>

• A generic stack that allows pushing and popping any type.

• Methods: push(), pop(), peek(), isEmpty().

• Throws NoSuchElementException if pop() or peek() is called on an empty stack.

• Example:

  Stack<String> stack = new Stack<>();
  stack.push("A");
  stack.push("B");
  System.out.println(stack.pop()); // B

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🧮 Part 2: Using Generics in Collections

🔹 CollectionsUtil.sort()

• Static generic method that sorts an ArrayList<T> where T extends Comparable<T>.

• Example:

  ArrayList<Integer> list = new ArrayList<>(List.of(5, 3, 9, 1));
  CollectionsUtil.sort(list);
  System.out.println(list); // [1, 3, 5, 9]

🔹 CollectionsUtil.printCollection()

• Accepts Collection<?> and prints each item (demonstrates wildcard use).

• Example:

  List<String> names = List.of("Alice", "Bob", "Carol");
  CollectionsUtil.printCollection(names);

🔹 CollectionsUtil.sumOfNumberList()

• Accepts List<? extends Number> and returns the sum as a double.

• Example:

  List<Number> nums = List.of(1, 2.5, 3L);
  double sum = CollectionsUtil.sumOfNumberList(nums); // 6.5

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🧠 Part 3: Complex Generic Scenarios

🔹 Cache<T>

• Stores instances of type T with retrieval by key.

• Uses a key extractor (Function<T, String>) passed into the constructor.

• Methods:

  • add(T item)
  • get(String key)
  • clear()
  • addAll(Cache<? extends T> other) — adds compatible cache entries using bounded wildcards.

• Example:

  Cache<Student> cache = new Cache<>(s -> s.lastName() + ":" + s.id());
  cache.add(new Student("Alice", "Brown", 1));
  System.out.println(cache.get("Brown:1"));

🔹 Student (Custom Comparable)

Implements Comparable<Student> for sorting by last name, first name, and ID.

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🧪 Test Cases for Demonstration Video

✅ Normal Test Cases

#	Feature	Expected Result
1	Pair<K, V>	Prints key-value and allows updating value
2	Stack<T> push/pop	Returns items in correct order
3	sort() utility	Correctly sorts integers, strings, and custom objects

⚠️ Edge Test Cases

#	Feature	Expected Result
1	Pop empty stack	Throws and catches NoSuchElementException
2	sumOfNumberList() with mixed types	Correctly sums integers, floats, doubles, longs
3	Cache<T>.clear()	Removes all items; size() returns 0

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🧩 Example Output

=== Part 1: Pair<K,V> ===
Pair{age = 36}
Updated: Pair{age = 37}

=== Part 1: Stack<T> ===
Stack: [A, B, C]
peek: C
pop: C
after pop: [A, B]
Caught expected underflow: Stack underflow: cannot pop from empty stack

=== Part 2: Sort Utility ===
Sorted ints: [1, 2, 5, 9]
Sorted strings: [Alpha, bravo, charlie, delta]
Sorted students: [Student{Anderson, Bob #2}, Student{Anderson, Cara #5}, Student{Brown, Alice #3}]

=== Part 2: Wildcards ===
printCollection(students):
Student{Anderson, Bob #2}
Student{Anderson, Cara #5}
Student{Brown, Alice #3}
sumOfNumberList: 11.25

=== Part 3: Cache<T> ===
studentCache: [Student{Clark, Dana #10}, Student{Brown, Evan #11}]
after addAll: [Student{Clark, Dana #10}, Student{Brown, Evan #11}, Student{Anderson, Fiona #12}, Student{Brown, Gina #13}]
containsKey(Brown:Evan#11): true
get(Brown:Evan#11): Student{Brown, Evan #11}
after clear, size=0

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🏅 Extra Credit Opportunities (+5%)

You can earn up to 5% extra credit by:

• Implementing a text-based CLI menu to interact with Stack and Cache.
• Building a simple GUI (Swing/JavaFX) to manage the cache visually.
• Writing a unit test suite (JUnit) covering all classes.

Include a short PDF describing your enhancements and how they improve the assignment.

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🧑‍💻 Author

Elida Ribeiro North Seattle College — Application Development BAS 📅 Due Date: November 3, 2025