CODEWITHSUNDEEP
javaarrays
Haluk
Haluk

Reputation: 3

How to increment an array of object when ever an object is created?

In my project, I was given the class given below. It works like, whenever a Flat object is created the array flats is incremented by one flat object. My question is how can I increment this array every time a flat object is created. Im really stuck on it. dont know where to start!

thx!

public class Block {

public Block() {
    super();
    flats = new Flat[0];
}



Flat[] flats;

class Flat {

    Room[] rooms;

    class Room {
        private int width;
        private int height;
        private int numWindow;

        public Room(int w, int h, int n) {
            super();
            this.width = w;
            this.height = h;
            this.numWindow = n;


        }

        @Override
        public String toString() {
            return width + "/" + height + "/" + numWindow;
        }
    }

    public Flat() {
        super();
        rooms = new Room[0];


    }
}
}

Upvotes: 0

Views: 261

Answers (4)

Adrian Klimczak
Adrian Klimczak

Reputation: 133

Can you sent this array to Flat's Constructor?

Code (based on your code):

public class Block {

    private Flat[] flats;

    public Block(Flat[] flats) {
        this.flats = flats;
    }

    public Flat[] getFlats() {
        return flats;
    }

    public void setFlats(Flat[] flats) {
        this.flats = flats;
    }


    @Override
    public String toString() {
        return Arrays.toString(flats);
    }


    public class Flat {

        private String value;


        public Flat() {
            //init your Flat
            this.value = UUID.randomUUID().toString();

            flats = Arrays.copyOf(flats, flats.length + 1);
            flats[flats.length - 1] = this;

        }

        @Override
        public String toString() {
            return value;
        }
    }
}

public class Main {

    public static void main(String[] args) {
        System.out.println("Test");
        Block block = new Block(new Block.Flat[0]);
        block.new Flat();
        block.new Flat();

        System.out.println(block.toString());
    }

}

Output: [b30c54dd-7e5d-46bc-81cf-18172e68337e, c22c4589-7563-4ada-a4eb-16226bd81f45]

Upvotes: 0

SirDarius
SirDarius

Reputation: 42899

Flat is Block's inner class, therefore, the flats member variable is directly accessible from the Flat class.

As per the documentation:

As with instance methods and variables, an inner class is associated with an instance of its enclosing class and has direct access to that object's methods and fields.

You can modify the Flat constructor like this:

public Flat() {
  super();
  rooms = new Room[0];

  // append the newly created flat into the flats array
  flats = Arrays.copyOf(flats, flats.length + 1);
  flats[flats.length - 1] = this;
}

This means the flats array will be copied for each new flat, which is arguably much less efficient than using an ArrayList.

While this works, I strongly recommend against having deeply nested class structures, and use a better dependency and ownership model. This is outside the scope of this question though.

Upvotes: 1

Mohamed Taher
Mohamed Taher

Reputation: 99

If you want to only count the objects, you don't need an array, you can use a static field called let's say NumOfObjects and increment it every time the constructor is created. However, if you wish to save the objects in an array I recommend you to use ArrayList in this case (as static field in Flat class) (documentation) instead of an array because of the fixed size of arrays in java, you'll have to create an array with fixed initial size and in the Flat constructor you should check if the array is full, you should create bigger array, copy the old one, and add the new object. ArrayList takes care of all that instead of you.

Upvotes: 0

rnv
rnv

Reputation: 27

Define flats array as static member of the class Block, and in the constructor of Flat push the newly created object.

Upvotes: 0

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