Wrong setting value in constructor using interfaces

Question

I get json which I need to parse to object with GSON:

"product":{
"product_type":"assignment",
"id":717,
    "product_profile":{
    "title":"new Order from java",
    "info":"Some special info",
    "dtl_expl":true,
    "special_info":""
    }
}

"product_profile" will be different object depend on what I get in "product_type". I created classes for each of that objects - Assignment and Writing. They are child of ProductType class. I implement interface in Product class which should return right object - Assignment or Writing depend on what value is in "product_type". My Product class

public class Product implements IProductType{
    ProductAssignment prodAss;
    ProductWriting prodWr;
    ProductType returnState;

    @SerializedName("id")
    int id;
    @SerializedName("product_type")
    String product_type;
    @SerializedName("product_profile")
    ProductType product_profile;
    public Product()
    {

    }
    public Product(int id, String product_type, ProductType product_profile)
    {
        this.id = id;
        this.product_type = product_type;
        this.product_profile = product_profile;
    }
    public int getProductId() 
    {
         return this.id;
    }
    public String getProductType() 
    {
         return this.product_type;
    }
    public ProductType getProduct() 
    {
         return this.returnObject(product_type);
    }
    public void setProductId(int id) 
    {
        this.id = id;
    }
    public void setProductTitle(String product_type) 
    {
        this.product_type = product_type;
    }
    public void setProduct(ProductType product_profile) 
    {
        this.product_profile =  this.returnObject(product_type);
    }
    @Override
    public String toString() {
        return "id=" + id + " " + "title=" + product_type
                + " " + "profile=" + product_profile  +  "}";
    }
    @Override
    public ProductType returnObject(String res) 
    {

        System.out.println("Product");
        System.out.println(product_profile);
        if (res.equals("assignment"))
        {
            this.product_profile = new ProductAssignment();
            System.out.println("I'm going to parse Assignment");
        }
        else if  (res.equals("writing"))
            this.product_profile =  new ProductWriting();

        return product_profile;

    }

}

But when I try to parse json to object like this:

  Gson gson = new Gson();
  Product product = gson.fromJson(res,Product.class);

I get such a product object:

id=447 title=assignment profile=ProductType@e49f9fa

so "id" and "product_type" parse correctly, but it is not Assignment object in ProdutType.

My ProductType class:

   public class ProductType implements IProductType{
    String product;

    static ProductType productType;
    static ProductAssignment productAssignment;
    static ProductWriting productWriting;
    IProductType component;

    ProductType returnState;
    ProductAssignment prodAss;
    ProductWriting prodWr;
    public ProductType()
    {       
    }
    public ProductType(IProductType c)
    {
         component = c;
    }
    public ProductType getProductType()
    {
        return this.returnState;
    }
    public void setProductType(ProductType returnState)
    {
        this.returnState = returnState;
    }
    @Override
    public ProductType returnObject(String product_type) 
    {
        if (product_type.equals("assignment"))
        {
            this.returnState = new ProductAssignment();
            System.out.println("I'm going to parse Assignment");
        }
        else if  (product_type.equals("writing"))
            this.returnState =  new ProductWriting();

        return returnState;
    }
    @Override
    public String toString()
    {
        return returnState.getClass().getName();
    }

}

yeah, I just did it...Maybe something wrong with my ProductType class? — Rikki Tikki Tavi, Nov 21 '12 at 10:12
I came across a similar issue recently. I solved it [here](http://stackoverflow.com/a/12459070/823393) using a `Deserializer`. — OldCurmudgeon, Nov 21 '12 at 10:38

score 0 · Accepted Answer · answered Nov 21 '12 at 09:57

0

Looks fine. To get correct output you need to override toString() in the ProductType class.

answered Nov 21 '12 at 09:57

jlordo

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when I try to override to string and return either ProductAssignment, either ProductType either result of returnObject interface I get NullPoinerException... – Rikki Tikki Tavi Nov 21 '12 at 10:03
I added ProductType class for my question - look please, maybe it something wrong with it? – Rikki Tikki Tavi Nov 21 '12 at 10:13
what will `..."profile=" + product_profile.getClass().getName()` print in `Produt` class print? – jlordo Nov 21 '12 at 10:27
I think your JSON represents some subclass of `ProductType` but you tell JSON to pares it to to `ProductType` class. How should GSON know wich subclass to use? – jlordo Nov 21 '12 at 10:35
I guess to organise classes in that way - when I get JSON, I detect "product_type" string and then make ProductType to those object, which corresponds the incomming object which the help of interfaces or another way. Can I do it in that way? – Rikki Tikki Tavi Nov 21 '12 at 10:38
Does GSON call your `returnObject` method? – jlordo Nov 21 '12 at 10:44
I guess no. But I want to detect what object should be ProductType in Product class. I want ProductType of Product return right object with the help of returnObject. – Rikki Tikki Tavi Nov 21 '12 at 10:49
1

look at [this](http://stackoverflow.com/questions/5800433/polymorphism-with-gson) – jlordo Nov 21 '12 at 10:54

Wrong setting value in constructor using interfaces

1 Answers1