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Problem in iterating HashMap

Keerthi Kumar
Ranch Hand

Joined: Apr 20, 2009
Posts: 105
Dear All,

I am facing an issue while iterating Hash Map. Through a query I am fetching list of users and list of emails of those users and i am adding those to a hash map as shown below:

But the valueMap object contains the required data from the database.
Request to please help me to resolve this issue

Keerthi Kumar N
Martin Vajsar

Joined: Aug 22, 2010
Posts: 3719

Why are you using an ArrayList as both a key and a value? The Map can hold multiple key-value pair on its own, you don't need to use lists to be able to put more keys/values into it. (Using a list as a key is very weird. And even if it had a merit in your case I don't see, it would still be dangerous, as the list is mutable; keys whose value can change cannot be used with a Map.)

The exception you're encountering is most likely caused because the utilDao.getUserEmailIds method is returning a null.

I'd suggest to read the Collections tutorial.
Campbell Ritchie

Joined: Oct 13, 2005
Posts: 44605
Martin Vajsar wrote: . . . keys whose value can change cannot be used with a Map. . . .
Oh, yes they can!

As long as you don’t mind all your references vanishing mysteriously whenever its hash code changes
I agree. Here's the link: http://aspose.com/file-tools
subject: Problem in iterating HashMap
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