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Eric Bruno

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JDK 8: Closure Syntax Decision

September 09, 2011

According to Brian Goetz, the expert group for the JCP in charge of JSR 335 and JDK 8 overall has come to a decision. The syntax for Java Closures, a.k.a. Lambda expressions or Project Lambda, will be close to that of C# for the same subject. Some details are still being decided, but in general, the syntax should look similar to the following:

(x, y) => { System.out.println("The sum of x and y equals " + (x+y) ) };

The decisions behind this syntax involve:

  1. Appearance: It looks nice and reads well in most cases, even complex ones with multiple lines of code.
  2. Familiarity: The proposed alternatives were no better in terms of usability and readability, and many were worse. Going with a syntax that was already in use with C# and Scala, and therefore familiar to many developers already, was thought to be the best choice.

According to Goetz, a compiler implementation will be available soon. For more on Closures and Lambda expressions, see the Project Lambda page, Closures for Java, and the JDK 8 Project page.

FYI, the syntax for C# clostures/lambda expressions:

   lambda = ArgList Arrow Body
   ArgList = Identifier
             | "(" Identifier [ "," Identifier ]* ")"
             | "(" Type Identifier [ "," Type Identifier ]* ")"
   Body = Expression
             | "{" [ Statement ";" ]+ "}"

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