Module 1: Sets

Learning Objectives

• Implement code to iterate over the elements of a Set to perform an operation on each one
• Implement code to add an object to a Set
• Implement code to remove an object from a Set
• Explain what the contents of a Set are after adding a duplicate value
• Explain why checking for the presence of an object in a HashSet or adding an object to a HashSet runs in constant O(1) time
• Design and implement a class that uses a Set as a member to ensure uniqueness
• Outline the purpose of a Set
• Compare and contrast the Set and List data structures
• Recall that HashSet is an implementation of Set

Code Examples

Here are some examples demonstrating key Set concepts:

Creating and Using a HashSet

import java.util.HashSet;
import java.util.Set;

public class SetExample {
    public static void main(String[] args) {
        // Creating a new HashSet
        Set<String> fruits = new HashSet<>();
        
        // Adding elements to the Set
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Apple");  // Duplicate - will not be added
        
        // Iterating over elements
        System.out.println("Fruits in the set:");
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
        
        // Checking if an element exists
        System.out.println("Contains Apple? " + fruits.contains("Apple"));
        
        // Removing an element
        fruits.remove("Banana");
        
        // Size of the Set
        System.out.println("Number of fruits: " + fruits.size());
    }
}

Using Set Operations

import java.util.HashSet;
import java.util.Set;

public class SetOperationsExample {
    public static void main(String[] args) {
        // First set
        Set<Integer> set1 = new HashSet<>();
        set1.add(1);
        set1.add(2);
        set1.add(3);
        set1.add(4);
        
        // Second set
        Set<Integer> set2 = new HashSet<>();
        set2.add(3);
        set2.add(4);
        set2.add(5);
        set2.add(6);
        
        // Union (create a new set with all elements)
        Set<Integer> union = new HashSet<>(set1);
        union.addAll(set2);
        System.out.println("Union: " + union);
        
        // Intersection (elements present in both sets)
        Set<Integer> intersection = new HashSet<>(set1);
        intersection.retainAll(set2);
        System.out.println("Intersection: " + intersection);
        
        // Difference (elements in set1 but not in set2)
        Set<Integer> difference = new HashSet<>(set1);
        difference.removeAll(set2);
        System.out.println("Difference (set1 - set2): " + difference);
    }
}