problem with collection

[Hengki Widjaja]

I have a class with content like this:

class Purchase{
private int purchaseCode;
private Date purchaseDate;
private List<PurchaseDetail> purchaseDetail; // this is the hard part

..... //other members
}

when I use field.get on purchaseCode or purchaseDate, no problem. but when I try to access the purchaseDetail(s), this technique gives me an error. help please? thanks

[Bear Bibeault]

Keeping the error a secret does not help us help you.

[Hengki Widjaja]

Oh, sorry. I forgot
the error message was : cannot convert from object to list.

[Harsha Smith]

TypeCast it to List. Please paste the entire code to help you better

[Hengki Widjaja]

class Purchase{
public int purchaseCode;  
public Date purchaseDate;  
public List<PurchaseDetail> purchaseDetail; // this is the hard part  
}

class PurchaseDetail{
public int item_id;

PurchaseDetail(int i){
  item_id=i;
}

}

public static void main(String[] args){
Purchase purchase=new Purchase();
purchase.purchaseCode=1;

List<PurchaseDetail> p =new ArrayList<PurchaseDetail>();
p.add(new PurchaseDetail(1));
p.add(new PurchaseDetail(2));
p.add(new PurchaseDetail(3));
purchase.purchaseDetail=p;

			try{
					Field f= purchase.getClass().getDeclaredField("purchaseDetail");
					List<PurchaseDetail> t=(List) f.get(purchase);
					for(PurchaseDetail d:t){
						System.out.println(d.item_id);
					}
						
			}catch (Exception e) {
				
				e.printStackTrace();
				
			}

}

Ah yes, forgot the typecast. it should return 1, 2 and 3. instead, it returned 0,0,3. am I missing something?

[Hengki Widjaja]

ahh, silly mistake. I forgot to change the value from the input file. but I have another question. I had to do this:

List<PurchaseDetail> t=(List) f.get(purchase)

to get the value. is there a more generic way, so I don't need to change this for every different type? thanks

[Paul Clapham]

No, that's the sort of thing you have to do when you use reflection. But why are you using reflection anyway?

[Harsha Smith]

It prints 1,2,3. Please recheck.

class PurchaseDetail{  
	private int item_id;  
	  
	PurchaseDetail(int i){  
	  item_id=i;  
	}  
	public static void main(String[] args){  
		Purchase purchase=new Purchase();  
		purchase.purchaseCode=1;  
		  
		List<PurchaseDetail> p =new ArrayList<PurchaseDetail>();  
		p.add(new PurchaseDetail(1));  
		p.add(new PurchaseDetail(2));  
		p.add(new PurchaseDetail(3));  
		purchase.purchaseDetail=p;  
		  
		            try{  
		                    Field f= purchase.getClass().getDeclaredField("purchaseDetail");  
		                    List<PurchaseDetail> t=(List<PurchaseDetail>) f.get(purchase);  
		                    for(PurchaseDetail d:t){  
		                        System.out.println(d.item_id);  
		                    }  
		                          
		            }catch (Exception e) {  
		                  
		                e.printStackTrace();  
		                  
		            }  
		  
		}  
	  
	}  

class Purchase{  
    int purchaseCode;    
	 Date purchaseDate;    
	 List<PurchaseDetail> purchaseDetail; // this is the hard part    
	}  

[Hengki Widjaja]

@Harsha:
yes, it was some silly mistake. it prints correctly now.

@Paul:
I use reflection to create some sort of simple class parser. So, I got assignment to make a basic ORM project. the class is used to take an object as a parameter and then translate that into a SQL insert string. in order to do this, I need to get the members of the object. now I'm struggling with the cascade insertion (i.e. the member of class that's a collection). any idea? thanks

[Hengki Widjaja]

Thanks for the help, guys. apparently the silly cast is all I need. what a blunder. thanks again. have a nice day!!
As for the cascade, actually it's just a thought. it's not required. so I'll just leave it at that. besides, I don't have any plan of competing with hibernate.