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Stream.map(...).reduce() as string joiner: error "left-hand side" [message #1807642]

Wed, 05 June 2019 13:44

Karsten Wutzke

Messages: 123
Registered: July 2009

Senior Member

Hello,

I found this JSF EL expression on the net:

<h:outputText value="#{companyBenutzerManager.selectedEntity.zulassungen.stream().map( zul -> zul.client.name ).reduce( ( p1, p2 ) -> p1 += ', ' += p2 ).get()}" />

What this does is simply produce a comma-separated list of client names to be displayed in a dialog - in one line. ;-)

I need the same on my bean however, to send an e-mail with this text. I then copied the line and changed it to pure Java like:

String str = getSelectedEntity().getZulassungen().stream().map( zul -> zul.getClient().getName() ).reduce( ( p1, p2 ) -> p1 += ", " += p2 ).get();

However, this doesn't compile.

Why?

The error in Eclipse is:

"The left-hand side of an assignment must be a variable"

Also see attachment.

Note, that I changed the code a little for better understanding.

Does anyone know why this shows an error in Eclipse? Why is it working in JSF EL but not in Java?

Thanks
Karsten

Attachment: 2019-06-05 15_38_18-eclipse-workspace - vdgauthportal_src_main_java_de_vdg_authportal_view_domain_Co.png
(Size: 52.96KB, Downloaded 21 times)

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Re: Stream.map(...).reduce() as string joiner: error "left-hand side" [message #1807667 is a reply to message #1807642]

Wed, 05 June 2019 21:09

Nitin Dahyabhai

Messages: 3850
Registered: July 2009

Senior Member

This is more a general Java question than an Eclipse question.

+= may be a valid string concatenation operator in JSF EL, but it means something very different in Java. You can't assign a new value to the literal " ,".

Nitin Dahyabhai
Eclipse Web Tools Platform

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Re: Stream.map(...).reduce() as string joiner: error "left-hand side" [message #1807704 is a reply to message #1807667]

Thu, 06 June 2019 13:25

Karsten Wutzke

Messages: 123
Registered: July 2009

Senior Member

Yeah, now that you say it...

String str = getSelectedEntity().getZulassungen().stream().map( zul -> zul.getClient().getName() ).reduce( ( p1, p2 ) -> p1 += ", " + p2 ).get();

Indeed += seems to something I had not expected. Changing the concat operator from += to + works.

Strange.

Thanks for helping on this.

[Updated on: Thu, 06 June 2019 13:26]

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