First: Getting rid of =>

Basically, when i read all the proposals, comments and pros and cons on closures in Java the first thing i would get rid of is the obviously redundant => declaration.

So in case of block statements the following would be allowed:

{
 int x = 0;
 int y = 3;
 int sum:= x+ y;
}

As i understood it right, => has at least two meanings. It means return for functions and := or = in the other case.

Replace => by := for assignments

I would use := for assignments rather than => simply because := is more naturial to mathematicians and logicians and is usually used to describe an assignment in math and logics. This could be used as outlined above:

{
 int x = 4;
 int y = 3;
 int z = 3;
 int sum:=x+y+z; //assignment
}

Use a function keyword instead of {int, int => int} syntax

For the function declaration, i would suggest to use a keyword rather than a symbol. Why not invent a function keyword that has a similar meaning like => i.g.:

public int function add(int x, int y){
return x + y;
}

In the other case, i would use := instad of => because the arrow direction implies to read it left to right rather than right to left and there is no <= to represant the invert direction.

Use a block keyword to declare block statements

Rather than just simply type closures i would invent a block keyword that defines a block of anonymous statements:

//only valid for anonymous block statements, not be used in loops 
//itereations

block{
 int x = 3;
 int y = 4;

}

So with these language features you could write a simple to read Java code that is clear and understandable by everyone:

class MyClass{
 //declare a function type
 public int function add(int x, int y){
    return x + y;
 }
 public int function sub(int x, int y){
  return x - y;
 }
 public void function(List intList){
    for(int i = 0; i < 10; i++){
        intList.add(i);
     }
  }
 public static void main(String[] args){
   
  //declare a closures block
   block{
     int x = 4;
     int y = 3;
    System.out.println("x + y" + (x+y));
    }
  }
 }

}