Removing objects from an array(Java)

Question

I have an owner class, which has an array of owned dogs. It looks like this:

public class Owner {
    
    private String ownerName;
    public Dog[] ownedDogs = new Dog[0];
    private int dogCount = -1;
    
    public Owner(String ownerName) {
        this.ownerName = ownerName;
    }
    
    public String getName(){
        return ownerName;
    }
    
    public void assignDog(Dog d) {
        
        Dog[] newOwnedDogs = new Dog[ownedDogs.length + 1];
        for (int i = 0; i < ownedDogs.length; i++) {
            newOwnedDogs[i] = ownedDogs[i];
        }
        ownedDogs = newOwnedDogs;
        
        this.ownedDogs[++dogCount] = d;
        makeOwner(this, d);
    }

   
   private void makeOwner(Owner o, Dog d) { 
        
        if(d.owner !=o) {
            d.owner = o;
        }
    }
    
    public boolean ownerOfDog(Dog d){
        if (d.getOwner() == this){
            return true;
        } else {
            return false;
        }
         
    }
    
    public String toString(){
        return "Name: " + ownerName;
    }

And the dog class looks like this:

public class Dog{
    private String name;
    private String breed;
    private int age;
    private int weight;
    private double tailLength;
    public Owner owner;
    

    public Dog(String name, String breed, int age, int weight) {
            this.name = name;
            this.breed = breed;
            this.age = age;
            this.weight = weight;
            
    }
   
    public String getName() {
        return name;
    }
    
    public String getBreed() {
        return breed;
    }
    
    public void increaseAge() {
        age++;
    }

    public int getAge() {
        return age;
    }

    public int getWeight() {
        return weight;
    }

    public double getTailLength() {
        if (breed.equalsIgnoreCase("dachshund") || breed.equalsIgnoreCase("tax")) {
            return 3.7;
        } else {
            return weight * (age / 10.0);
        }
    }
    
    public Owner getOwner(){
        return owner;
    }
    
    public void setOwner(Owner o) {
        if(this.owner != o) {
            this.owner = o;
            o.assignDog(this);
        }
    }
    
    public String toString() {
        return "Name: " + name + " Breed: " + breed + " Age: " + age + " Weight: " + weight + " Tail length: " + getTailLength() + " owned by: " + owner;
    }
}

And I am trying to create a method to remove a dog from the array, this is what i currently have:

public void removeDog () {
        
        System.out.println("Enter the name of the dog?> ");
        String name = input.nextLine();
        
        Owner o = findOwner(name);
        Dog d = findDog(name);
        
        if(d == null) {
            System.out.println("Error: no such dog");
            
        } else {

            //Code to remove dog from o.ownedDogs
            
        }
            System.out.println(name + " is removed from the register");
    }

Is there a good way to remove objects from an array without manually entering the index of the element? I have seen examples using other data types, but I am a beginner in java, so I am having trouble applying it here.

Is there a reason why your code uses Dog[] to store the dogs owned by an owner? I think with a different data structure like a Map everything would become way easier. — Matteo NNZ
– Matteo NNZ, Commented Jul 30, 2021 at 0:04
Yes, you can loop through the list of dogs, for example: for (int i = 0; i < ownedDogs.length; i++) {if(d == ownedDogs[i]) ownedDogs[i] = null;} — sorifiend
– sorifiend, Commented Jul 30, 2021 at 0:04
Is there a good way to remove objects from an array without manually entering the index of the element? - not really. That is why other classes, like ArrayList exist. Those classes implement methods, like remove(...) to alter the items in an Array. Trying to implement a remove method in an Array is reinventing the wheel. — camickr
– camickr, Commented Jul 30, 2021 at 0:07

Bohemian · Accepted Answer · 2021-07-30 00:31:36Z

2

The problem with using an array is removing an object it actually non-trivial, because you must:

Create a new array of size 1 less than the current one
Find the index of instance
If not found, stop
Copy all elements from the old to the new array up to the index
Copy all elements from the old to the new up array after the index
Swap out the old for the new array in your instance

That is all "too hard" compared with:

public List<Dog> ownedDogs = new ArrayList<>();

then

ownedDogs.remove(d);

You would need to implement equals() (and hashCode()) in the Dog class.

As a general rule, never use an array when you could use a Collection.

You should probably use Set<Dog> ownedDogs = new HashSet<>(); and make ownedDogs private and provide a getter for it.

answered Jul 30, 2021 at 0:31

Bohemian♦

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GreyBeardedGeek · Accepted Answer · 2021-07-30 02:46:51Z

1

From a functional perspective, and assuming that as in your example, the Dog's name is a unique identifier, you would produce a new array by filtering the initial array:

ownedDogs = Arrays.stream(ownedDogs)
.filter(dog -> !dog.name.equals(nameToRemove))
.toArray();

answered Jul 30, 2021 at 2:46

GreyBeardedGeek

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mono832 · Accepted Answer · 2021-07-30 02:11:54Z

0

Arrylists would solve this, It could be implemented something like this

public ArrayList<Dog> ownedDogs=new ArrayList<>();

and use

ownedDogs.remove(index);

unlike regular arrays they can have no defined size and once you remove an object from them the index's will all shift accordingly

answered Jul 30, 2021 at 2:11

mono832

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