Clear and Clone

Part of the Logic & Flow section of Coddy's Java journey — lesson 27 of 59.

The clear() method removes all elements from a HashSet, leaving it empty.

The clone() method returns a shallow copy of the HashSet. (The elements themselves are not cloned.)

For example, first create a HashSet:

HashSet<String> set = new HashSet<>();
set.add("Coddy");

To clone the set:

HashSet<String> clonedSet = (HashSet<String>) set.clone();
System.out.println(clonedSet);
// Output: [Coddy]

To clear the set:

set.clear();
System.out.println(set.isEmpty());
// Output: true

Why do we need casting with clone()?

You've already learned about casting with primitive types (like int x = (int) 3.14). The same concept applies to objects, but for a different reason.

The clone() method returns a generic Object type, not a specific HashSet<String>. This is because clone() is defined in the Object class and doesn't know what type you're cloning.

// What clone() returns:
Object cloneResult = set.clone();  // Returns Object, not HashSet<String>

// What we need:
HashSet<String> clonedSet = (HashSet<String>) set.clone();  // Cast Object → HashSet<String>

The cast tells Java: "I know this Object is actually a HashSet<String>, so treat it as one."

Without the cast, you'll get a compilation error because Java won't automatically convert Object to HashSet<String>.

Challenge

Easy

Create a method named <strong>processSet</strong> that takes a HashSet of Strings as input. The method should:

Clone the set.
Clear the original set.
Print the cloned set and its size in the format:
Cloned Set: [elements]
Cloned Set Size: X
Print the original set (after clear) and its size in the format:
Original Set after clear: [elements]
Original Set Size: Y

Cheat sheet

The clear() method removes all elements from a HashSet:

set.clear();

The clone() method returns a shallow copy of the HashSet:

HashSet<String> clonedSet = (HashSet<String>) set.clone();

Why casting is needed: The clone() method returns a generic Object type, so you must cast it to HashSet<String> to use it as the specific type.

Example usage:

HashSet<String> set = new HashSet<>();
set.add("Coddy");

// Clone the set (cast Object → HashSet<String>)
HashSet<String> clonedSet = (HashSet<String>) set.clone();

// Clear original set
set.clear();
System.out.println(set.isEmpty()); // Output: true
System.out.println(clonedSet);      // Output: [Coddy] (clone unaffected)

Try it yourself

import java.util.HashSet;
import java.util.Scanner;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;
@SuppressWarnings("unchecked")

public class Main {
    public static void processSet(HashSet<String> set) {
        // Write your code here
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String setString = scanner.nextLine();
        
        Type setType = new TypeToken<HashSet<String>>(){}.getType();
        HashSet<String> set = new Gson().fromJson(setString, setType);
        
        processSet(set);
    }
}