A λ (lambda) is an anonymous function. In addition to Closures, Oracle are looking at including lambdas in JDK 7, which would bring more functional goodness to the feature stagnant Java. This InfoQ article sums up the situation nicely. It talks about the difference between lambdas and closures – a closure is a function that doesn’t rely on any external arguments – it is a closed function. However, a lamda is an open function.
λx. x + y (open function, depends on y)
λy. λx. x+y (closed function, the inner open lambda is satisfied by y being supplied in the external function)
The former reminds me of Groovy’s closure currying
The proposed syntax looks something like this
inc = #(int x) (x+1); // single expression
inc2 = #(int x) { return x+1; }; // block
The rest of the article talks about the proposed syntax for lambdas and the concerns with implementing in various code constructs that potentially conflict with existing Java language syntax and rules.