in Java ArrayList

Question

I have declared this:

private ArrayList<? extends Transaction> transactionArray;

I want to add subclasses of Transaction to transactionArray, like so:

public void pushTransaction( Transaction theTrans ) {
    transactionArray.add( theTrans ); 
}

But this is rejected with the message

The method … is not applicable for the arguments…

Do I have to write a separate pushTransaction method for every subclass of Transaction? Or how can I make this method accept Transaction and its subclasses as valid arguments? Update: does it make any difference that I have declared Transaction as an abstract class, and am only dealing with its subclasses?

Have you tried just using `private ArrayList transactionArray;`? [Generics Trail](https://docs.oracle.com/javase/tutorial/java/generics/) might help — MadProgrammer, Jul 24 '15 at 02:42
*"(and why doesn't inserting 4 spaces before each line of code work?)"* Because it needs to be separated on a different line...like I have done, twice now... — MadProgrammer, Jul 24 '15 at 02:43
In particular [Upper Bounded Wildcards](https://docs.oracle.com/javase/tutorial/java/generics/upperBounded.html) — MadProgrammer, Jul 24 '15 at 02:44
The Upper Bounded Wildcards seems to say that (in my case), methods should be able to access the ArrayList elements as objects of type Transaction. That's what I'm trying to do, but it's rejected. — user3238181, Jul 24 '15 at 02:53
Compile. Also please see my added note about Transaction being declared abstract — user3238181, Jul 24 '15 at 03:04

score 0 · Answer 1 · answered Jul 24 '15 at 02:57

0

You don't need to use the generics syntax. . Your method should work as ling as you are passing a Transaction object or subclass of Transaction. Make sure your class actually extends Transaction. Also there may be more than one class called Transaction so check the package as well.

answered Jul 24 '15 at 02:57

Paul Howells

51
8

Good tips, thanks; I'll investigate (but the class definitely extends Transaction, with no compile errors). But if this isn't a place to use the generics syntax, then what is it for? – user3238181 Jul 24 '15 at 03:06
hi welcome to SOF and please read how to write a good answer here: http://stackoverflow.com/help/how-to-answer. you must provide a code sample or some snippet to help to understand the answer. – Nomesh DeSilva Jul 24 '15 at 03:16

in Java ArrayList

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