Why does this method reference assignment compile?

Question

I'm struggling to see why the following code compiles:

public class MethodRefs {      public static void main(String[] args) {         Function<MethodRefs, String> f;          f = MethodRefs::getValueStatic;          f = MethodRefs::getValue;     }      public static String getValueStatic(MethodRefs smt) {         return smt.getValue();     }      public String getValue() {         return "4";     }  } 

I can see why the first assignment is valid - getValueStatic obviously matches the specified Function type (it accepts a MethodRefs object and returns a String), but the second one baffles me - the getValue method accepts no arguments, so why is it still valid to assign it to f?

Answer 1

The second one

f = MethodRefs::getValue; 

is the same as

f = (MethodRefs m) -> m.getValue(); 

For non-static methods there is always an implicit argument which is represented as this in the callee.

NOTE: The implementation is slightly different at the byte code level but it does the same thing.