Return "this" in java instead of cloning objects.

http://fluffyelephant.com/2011/06/return-this/

by hmottestad • 15 years ago

4 8 15 years ago

fluffyelephant.com

slifty• 15 years ago

Taking a lesson from jQuery I see.

TNO• 15 years ago

Fluent interfaces predate jQuery

AndrewDucker2• 15 years ago

Only useful if you do not mind your objects being mutable.

otherwise:

  string name1 = "Andrew Ducker";
  string name2 = name1;
  name1.toUpper();

means that name2 is now also "ANDREW DUCKER" when we quite possibly didn't want it to be.

hmottestad• 15 years ago

Yes. In such a case you would need to clone the object. Having toUpper() clone by default is wasteful if you don't need a clone. Hence using "return this".

AndrewDucker2• 15 years ago

And I would argue that the reason that C# and Java have both gone for making strings immutable is that it is less confusing.

I value code that's less confusing over code that allocates extra objects (largely because the last time I wrote some simple benchmarking code I could allocate multiple millions of an object in a second).

sausagefeet• 15 years ago

I totally thought this post was going to be about methods just recording what the user wanted to do in a list and then have an apply method at the end. I'm not sure why I thought that...

asymptotic• 15 years ago

The idea of chained calls all returning this forms the basis of the phenomenally useful Builder Pattern, from Bloch's "Effective Java".

There are three main reasons for using the Builder Pattern:

1) Allows for "constructor-like" calls to functions that don't necessarily share the name of the class.

2) Allows for complex, multi-parameter "constructor-like" calls without needing to make one massive function call.

3) Allows intermediate argument checking on particular constructor arguments, and allows sane optional constructor arguments.

(I find this pattern very useful).

See:

http://rwhansen.blogspot.com/2007/07/theres-builder-pattern-...

http://stackoverflow.com/questions/5007355/builder-pattern-i...

https://manuelselva.wordpress.com/2010/04/09/effective-java-...

Return "this" in java instead of cloning objects.

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