将对象放入另一个对象数组内部的对象数组

Question

So I'm new to coding/Java and I'm working on this project. My assignment is to create 3 different classes (which I have here) and make a them cooperate. I've successfully made my FishTankManagerApp class retrieve a new Fish object and I'm trying to figure out how to put it in a FishTank object.

My FishTank class only is only there to create an array object which can hold 5 fish (I think I've done this correctly). In my FishTankManagerApp class, I've created an array of 10 of these FishTank Objects.

My question which I cant figure out for the life of me is how do I place the Fish objects into a specfic FishTank object after they've been created (I've made a note at the end of the code where I've ran into a problem).

Essentially I know I'm trying to put an object I've created inside of and array which contains another array where fish objects can be stored... I think....

Any help would be much appreciated! Thank you!

import java.util.Scanner;

public class Fish {

    private static Scanner stdin = new Scanner(System.in);
    private String userInput;
    private int userInput2;
    public boolean mean;
    public String name;

    public Fish(){      
        System.out.println("What is your fishes name?");

        userInput = stdin.next();
        this.name = userInput;

        System.out.println("Is this fish aggressive?\n"+
                           "(1)Yes\n(2)No");

        userInput2 = stdin.nextInt();
        if (userInput2 == 1)
            this.mean = true;
        else
            this.mean = false;
    }
}

public class FishTank {

    public FishTank(){

        Fish[] tank = new Fish[5];

    }
}

import java.util.Scanner;

public class FishTankManager {

    private static Scanner stdin = new Scanner(System.in);
    private static int userInput;
    private static FishTank[] tanks = new FishTank[10];

    public static void main (String[] args) {


        while (true){
            System.out.println("Welcome to your new fish tank manager!\n"+
                               "What would you like to do?\n"+
                               "(1)Add a Fish\n(2)Move a Fish\n"+
                               "(3)Check a tank");          
            userInput = stdin.nextInt();

            if (userInput == 1){
                Fish fish = new Fish();     
                System.out.println(fish.name);
                System.out.println(fish.mean);  

                changeTank(fish);

            }
            else if(userInput ==2){
            }
            else{
            }
        }
    }

    private static void changeTank(Fish fish){

        System.out.println("Which tank would you like to put this fish in? (1-10)");
        userInput = stdin.nextInt();

        tanks[userInput] = fish;
        // This last line is where I'm confused on how to put the fish() object into a tank which I've created.
    }
}

Answer 1

I'd recommend adding a method to your FishTank to make adding the fish easy. Maybe something like this:

public FishTank(){

    private Fish[] tank = new Fish[5];

    public boolean addFish(Fish fish) {
        // ... add code here to put the fish to the tank array
        // return true if there was room in the tank, false otherwise
    }
}

Note that the tank variable is now private. It's generally a good idea to keep member variables private in Java, and use methods to access them.

Then, where you've got the comment you mentioned, you can just call the new method:

boolean addedSuccessfully = tanks[userInput].addFish(fish);

You may not need to return the boolean as I'm showing, but it might be handy if you need to check whether the array (ie the tank) had room for the new fish.

Answer 2

Currently, what you're doing is setting the FishTank object equal to a Fish instance - not adding it to the tank variable inside of FishTank.

Right now, you have no way of accessing the tank variable inside of the FishTank class. What you need to do is make it a global variable and provide accessor/modifier methods. For example:

public class FishTank {

private Fish[] tank;
private int numFish;

public FishTank(){

    this.tank = new Fish[5];
    this.numFish = 0;

}

public void add(Fish f){
    if(this.numFish >= 5){
        //handle "tank is full" case
    }
    else{
        numFish++;
        this.tank[numFish] = f;
    }
}
}

Then invoke add on the desired FishTank object:

tanks[userInput].add(fish);