Here you go DaWolf

import java.util.ArrayList; // Imports
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main{ // Class declaration

    public static void main(String args[]){ // Main method

        String[] inv = {"rock", "knife", "spoon", "sword"}; // Making array
        List<String> cInv = new ArrayList<String>(Arrays.asList(inv)); // Converting array to ArrayList
        Scanner scanner = new Scanner(System.in); // Creating scanner
        System.out.println("Welcome to the game. Your inventory is: ");
        for(String item : cInv){
            System.out.println("- " + item); // Printing out all strings in the converted inventory
        }
        System.out.println("Press any key to continue.");
        scanner.nextLine(); // Waiting for user input
        System.out.println("Do you wish to add a stick, pebble or pokeball to your inventory?");
        String input = scanner.nextLine(); // Read new user input
        if(input.equalsIgnoreCase("stick") || input.equalsIgnoreCase("pebble") || input.equalsIgnoreCase("pokeball")){ // Check if item valid
            cInv.add(input.toLowerCase()); // Add item to converted inventory
            System.out.println("You added the item " + input + " to your inventory!");
            System.out.println("Your new inventory:");
            for(String item : cInv){
                System.out.println("- " + item); // Printing out all strings in the converted inventory (new item has been added)
            }
        }else{
            System.out.println("Sorry, but that item does not exist."); // Invalid item
        }
        inv = cInv.toArray(new String[cInv.size()]); // Converting converted inventory back to array
        scanner.close(); // Closing scanner to prevent resource leak
    }
}