Practice Set 2: Collections, Inheritance & Exceptions

Take a Moment to Think

These tasks are a step up from Practice Set 1 — this time you'll practice on your own by combining the collections, OOP inheritance/polymorphism, and exception handling concepts from the Intermediate/Advanced chapters. You'll get hands-on practice working with ArrayList and HashMap in real-world scenarios, putting abstract classes and subclasses into an array and looping through them with polymorphism, and handling exceptions with try-catch-finally. Since these tasks are harder, we recommend reviewing each concept before diving in.

Exercises

Task 1: Build an ArrayList<String> shopping list, add/remove items, and print it out using an enhanced for-loop. Task 2: Build a HashMap<String, Integer> inventory, practice put(), get(), containsKey(), and remove(), and loop through it with entrySet(). Task 3: Build an abstract class Shape (with an abstract area() method) and implement it with two subclasses, Circle and Rectangle — put both objects into a Shape[] array, then loop through it, calling area() and printing the result (polymorphism). Task 4: Write a divide(int a, int b) method that throws an ArithmeticException when b==0 — catch the error with a try-catch-finally block, and print an 'Operation complete' message in the finally block.

• You can practice ArrayList and HashMap operations (add, remove, put, get, entrySet) without errors
• You can implement an abstract class/subclass and loop through an array using polymorphism
• You can correctly handle an ArithmeticException with a try-catch-finally block

Code Example

import java.util.ArrayList;
import java.util.HashMap;

abstract class Shape {
    abstract double area();
}

class Circle extends Shape {
    double radius;
    Circle(double radius) { this.radius = radius; }
    double area() { return Math.PI * radius * radius; }
}

class Rectangle extends Shape {
    double width, height;
    Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    double area() { return width * height; }
}

public class Practice2 {
    public static void main(String[] args) {
        // Task 1: ArrayList shopping list
        ArrayList<String> shoppingList = new ArrayList<>();
        // TODO: add/remove items ပြီး enhanced for-loop နဲ့ print ပါ

        // Task 2: HashMap inventory
        HashMap<String, Integer> inventory = new HashMap<>();
        // TODO: put/get/containsKey/remove သုံးပြီး entrySet() နဲ့ loop ပါ

        // Task 3: Shape polymorphism
        Shape[] shapes = { new Circle(5), new Rectangle(4, 6) };
        // TODO: loop ပြီး each shape ရဲ့ area() ကို print ပါ

        // Task 4: Exception handling
        // TODO: divide(int a, int b) method ရေးပြီး b==0 ဖြစ်ရင် ArithmeticException throw လုပ်ပါ
        // try-catch-finally နဲ့ handle ပါ
    }
}

For all 4 tasks, your program should print the updated shopping list, the inventory data, the two shape areas, and the exception error message plus the finally message to the console.