Are there any reasons why specifying the argument type is required in Java 8 lambda syntax?

Question

I have read http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-4.html and noticed that all the examples have argument type declared explicitly, even though it's already known from the interface-function declaration.

public interface FileFilter {
    /** ... **/
    boolean accept(File pathname);
}


FileFilter java = (File f) -> f.getName().endsWith(".java");

Can't we go with just

(f) -> f.getName().endsWith(".java"); ?

UPDATE: In the JSR-335 Draft, I have found that inferred-type parameters are most likely to be supported

(int x) -> x+1 // Single declared-type parameter
(int x) -> { return x+1; } // Single declared-type parameter
(x) -> x+1 // Single inferred-type parameter
x -> x+1 // Parens optional for single inferred-type case