Reading File not reading properly-CodePudding

I feel like I'm making a dumb mistake because I've been able to do this successfully before, I'm trying to read a file to an Object ArrayList, here's the method.

public static void readFile (String fileName, ArrayList <Pokemon> newPokedex) {
    try{
        FileInputStream readData = new FileInputStream(fileName);
        ObjectInputStream readStream = new ObjectInputStream(readData);
        newPokedex = (ArrayList<Pokemon>) readStream.readObject();
        readStream.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

It'll work if I don't add parameters, but every time I do, it tells me my ArrayList is empty.

public static void main (String [] args) {
    Pokemon.readFile("Pokedex.txt", Pokemon.Pokedex);
    System.out.println(Pokedex.size());
}

My write method works just fine and it'll also print the correct size when I tell it to print it in the method

CodePudding user response：

Your error lies in the way you are using the

ArrayList <Pokemon> newPokedex

parameter.

In this line:

newPokedex = (ArrayList<Pokemon>) readStream.readObject();

you are not reading into the list that you provided as a parameter, instead you are overriding the list reference where the parameter is pointing. But that does not change the list reference outside your method. This is a common mistake.

If you use this line of code instead of the original, it should work:

newPokedex.addAll((ArrayList<Pokemon>) readStream.readObject());

Now you are actually adding all the items from the list that you read from the file into the list that you have provided as a parameter.