在对象数组中查找重复项

Question

The purpose of this project is to make a pokedex that adds and holds all the pokemon passed in by user input. When the user inputs a pokemon that is already stored in the pokedex the word "duplicate" is supposed to be printed to the console. The word duplicate is printed even though there are no actual duplicates within the object array. Here is my output from the console :

Welcome to your new PokeDex! How many Pokemon are in your region?: 3

Your new Pokedex can hold 3 Pokemon. Let's start using it!

1. List Pokemon
2. Add Pokemon
3. Check a Pokemon's Stats
4. Sort Pokemon
5. Exit

What would you like to do? 2

Please enter the Pokemon's Species: red Duplicate

Now here is all the code used that could possibly be making this error

import java.util.Scanner;

public class Project4 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Welcome to your new PokeDex!");
        System.out.print("How many Pokemon are in your region?: ");
        int size = input.nextInt();
        Pokedex pokedex = new Pokedex(size);
        System.out.println("\nYour new Pokedex can hold " + size + " Pokemon. Let's start using it!");
        int choice = 0;
        boolean done = false;

        while (!done) {
            System.out.println("\n1. List Pokemon\n2. Add Pokemon\n3. Check a Pokemon's Stats" + "\n4. Sort Pokemon\n5. Exit");
            System.out.print("\nWhat would you like to do? ");
            choice = input.nextInt();

            switch (choice) {
                case 1:
                    String[] pokemonList = pokedex.listPokemon();
                    if (pokemonList == null)
                        System.out.println("Empty");
                    else
                        for (int i = 0; i < pokemonList.length; i++) {
                            System.out.println((i + 1) + ". " + pokemonList[i]);
                        }
                    break;
                case 2:
                    System.out.print("\nPlease enter the Pokemon's Species: ");
                    String species = input.next();
                    pokedex.addPokemon(species);
                    break;
            }
        }
    }
}

In the following class I have the actual method that adds the pokemon and the constructor for Pokedex

public class Pokedex {
    Pokemon[] pokedex;
    String pokeArray[];

    public Pokedex(int size) {
        pokedex = new Pokemon[size];
        pokeArray = new String[size];
    }

    public boolean addPokemon(String species) {
        Pokemon stuff = new Pokemon(species);

        for (int i = 0; i < pokedex.length; i++) {
            if (pokedex[i] == null) {
                pokedex[i] = stuff;
            }

            else if (i < pokedex.length && pokedex[i] != null) {
                System.out.println("Max");
            }

            if (pokedex[i].getSpecies().equalsIgnoreCase(species)) {
                System.out.print("Duplicate");
                break;
            }
        }

        return false;
    }
} 

Sorry for the mass amounts of code I just need help tracing where this unexpected result is coming from.

Answer 1

The reason it's doing that is because of this bit of code here:

public boolean addPokemon(String species)
{
    Pokemon stuff = new Pokemon(species);
    for (int i = 0; i < pokedex.length; i++)
    {
        if (pokedex[i] == null)
            pokedex[i] = stuff;
        else if (i < pokedex.length && pokedex[i] !=null)
            System.out.println("Max");
        if(pokedex[i].getSpecies().equalsIgnoreCase(species))
        {
            System.out.print("Duplicate");
            break;
        }
    }
   return false;
}

The problem is just a little bit of syntax missing. In your for loop, you check to see if

A) there are any empty spots in the array

B) if every element in the array up to the user inputted size is full

and C) if any element in the array matches the one we're trying to add.

The problem you're encountering is because your C is an if instead of an else if . Because A sees the index is null, it assigns the new Pokemon to the Pokedex. Then because C is an if instead of an else if, it runs after you assign the new Pokemon and sees the Pokemon we just added and says it's a duplicate. Changing it to an else if would fix this.

Also, since there was no break; in A, it would assign every element of the array to the first one entered, causing any further additions to call Max. I edited the code and this is what I had that worked for me:

public boolean addPokemon(String species)
{
    Pokemon stuff = new Pokemon(species);
    for (int i = 0; i < pokedex.length; i++)
    {
        if(pokedex[i] !=null && pokedex[i].getSpecies().equalsIgnoreCase(species))
        {
            System.out.println("Duplicate");
            break;
        }
        else if (pokedex[i] == null)
        {
            pokedex[i] = stuff;
            break;
        }
        else if(i + 1 == pokedex.length)
        {
            System.out.println("Max");
            break;
        }
    }
   return false;
}

Also, out of curiosity, why is the addPokemon() function a boolean? You return a value (albeit arbitrarily) and then never do anything with that value. You could just make it a void, have it return nothing, and it would work just as fine.