The document discusses Project Lambda which aims to add lambda expressions to Java, allowing the creation of anonymous functions. It proposes a syntax using #() for lambda expressions and introduces function types to allow functions to be used as arguments or returned from methods. Key aspects that would be enabled include anonymous functions, function types, lambda expression syntax, functions as arguments, and support for single abstract method interfaces.

1. Project Lambda or #()(”Project Lambda”) 2010-04-29

2. Lambda Expressions (aka Closures) “ a first-class function with free variables that are bound in the lexical environment” - Wikipedia HUGE debate about various closures decision earlier BGGA, CICE, FCM, … Oracle seems to have decided this without JSR/JCP - most likely that this will be included in Java 7 Straw-Man Proposol - first-class functions - function types - lambda expression Syntax and content not definite, may change Complexity budget reached?

3. Lambda Expressions – Suggested Syntax A new way of writing anonymous functions A functions which take an int and returns its double #() (42) //no args, returns 42 #(int x) (x+x)

4. Lambda Expressions Complex expressions #(int x, int y){ int z = expensiveComputation(x, y); if (z < 0) return x; if (z > 0) return y; return 0; }

5. Function Types Every expression in Java must have a type, i.e. introduce function types … and they could be invoked #int() fortyTwo = #()(42); #int(int) doubler = #(int x)(x + x); assert fortyTwo() == 42; assert doubler(fortyTwo()) == 84;

6. Functions as arguments Methods can take a function as an argument public int[] map(int[] a, #int(int) fn) { int[] b = new int[a.length]; for (int i = 0; i < a.length; i++) b[i] = fn(a[i]); return b; }

7. SAM types Interfaces with just one method (SAM) Thread th = new Thread(new Runnable() { public void run() { doSomeStuff(); doMoreStuff(); } }); Thread th = new Thread(#(){ doSomeStuff(); doMoreStuff(); } )

8. Variable Capture shared int count = 0; Collections.sort(data, #(String a, String b){ count++; return a.length() - b.length()}); System.out.println(count);