Deep Copy of Object Array Instance, Java

Question

I have an object made in my main Recipe recipeOne = new Recipe("Pepperoni Pizza");

This object is an instance of this Object Array defined and constructed here!

public class Recipe implements Cloneable{

String Name;

final int INGREDIENT_ARRAY_MAX = 10;

Ingredient Recipe[] = new Ingredient[INGREDIENT_ARRAY_MAX];

public Recipe(String name){

    Name = name;

}

So I am looking to make a deep copy of this object with the line Recipe ressippi = (Recipe) recipe.clone(); and it sends me here!

public Object clone(){

    Recipe cloneRec = new Recipe(Name);

    return cloneRec;

}

I know this is currently a shallow copy because the method only passes references, so if I was to attempt a name change on my new Object that was a clone of recipeOne...it would change both of their names. Obviously I do not want that, I'm fairly lost on this, can anyone help?

EDIT:@Rohit Jain

Both my Recipe class as well as my Ingredient class (the objects the recipe array holds) have toString methods and recipes calls on ingredients in order to print it all out in a nice little format. When I call it on my "recipeOne" object (the one called pepperoni pizza) i get "Pepperoni Pizza: 1.0 Pounds of Dough, 8.0 Ounces of Sauce, 10.0 Ounces of Cheese"

Then I proceed to make the object ressippi and set that to the clone of recipeOne, so all good from here...then I change ressippi's name to "Pineapple Pizza" and that prints out fine but it doesnt print the 3 ingredient objects that recipeOne stored, which it is suppose to do!

See this answer: [link](http://stackoverflow.com/a/64066/1809603) — Can Yegane, Feb 11 '13 at 09:51

score 3 · Accepted Answer · answered Feb 11 '13 at 10:17

Add a copy constructor to the recipe class, which creates a new instance of recipe and copies all of the fields from an original recipe.

Recipe.java

public class Recipe implements Cloneable {

    String name;

    final int INGREDIENT_ARRAY_MAX = 10;

    Ingredient[] ingredients = new Ingredient[INGREDIENT_ARRAY_MAX];

    public Recipe(String name) {
        this.name = name;
    }

    //Copy Constructor
    private Recipe(Recipe recipe){
        this.name = recipe.name;
        for(int x = 0; x < recipe.ingredients.length; x++){
            this.ingredients[x] = recipe.ingredients[x];
        }
    }

    public static Recipe newInstance(Recipe recipe){
        return new Recipe(recipe);
    }

    //Debug Method
    public static void printRecipe(Recipe recipe){
        System.out.println("Recipe: " + recipe.name);
        for(Ingredient i:recipe.ingredients){
          if(i != null && i.getName() != null){
              System.out.println("Ingredient: " + i.getName());           
          }
        }
    }

    //Test Method
    public static void main(String[] args) {
        Recipe recipe = new Recipe("Chicken Soup");
        recipe.ingredients[0] = new Ingredient("Chicken");
        recipe.ingredients[1] = new Ingredient("Broth");

        Recipe copy = new Recipe(recipe);
        copy.ingredients[2] = new Ingredient("Rice");
        copy.name = "Chicken Rice Soup";

        printRecipe(recipe);
        printRecipe(copy);
        System.out.println(recipe == copy);
        System.out.println(recipe.ingredients == copy.ingredients);
    }
}

Ingredient.java

public class Ingredient {

    private String name;

    public Ingredient(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }


    public void setName(String name) {
        this.name = name;
    }
}

It is so old answer already, but I think "this.ingredients[x] = recipe.ingredients[x];" should not be done in a **deep copy**. You need to further do the deep copy of each element again. — Nguyễn Hoài Nam, Jan 24 '17 at 00:59

score 1 · Answer 2 · edited May 23 '17 at 12:17

As you have found out, implementing the Cloneable doesn't actually clone the object. You'll have to implement the clone() method sensibly, and if you want a deep copy, that's what you should implement.

Now, creating a new Recipe object with the same Name attribute is quite OK. And changing the name for the new object afterwards is also quite okay, it won't change the name of the first object as java String's are immutable.

You may want to have a look at the commons-beanutils package, which provides handy code for cloning objects.

Finally, as for "...only passes references..." you should read eg. this and this thread.

Cheers,

Magnus O. · Answer 3 · 2013-02-11T10:01:51.887

Serialize it! Take a look at the deepClone function as exampled here: http://www.avajava.com/tutorials/lessons/how-do-i-perform-a-deep-clone-using-serializable.html

The other replies on Strings being immutable are true of course, but the problem you tried to describe with the String example was just a bad example; complexer objects like the Ingredients array still is copied-by-reference.

Also: change the name of your array so that it doesn't match the class name (=confusing):

Ingredient Recipe[] = new Ingredient[INGREDIENT_ARRAY_MAX];

Deep Copy of Object Array Instance, Java

3 Answers3