What is the difference between `lookup.unreflect()` and `lookup.findVirtual()`?

Question

There are 2 ways i have tried to obtain the MethodHandle to a given function.

Method 1

Method m = MyClass.class.getMethod("myMethod", String.class, Map.class);
MethodHandle mh = MethodHandles.lookup().unreflect(m);

Method 2

MethodType type = MethodType.methodType(void.class, String.class, Map.class);
MethodHandle mh = MethodHandles.lookup().findVirtual(MyClass.class, "myMethod", type);

What is the difference between both of them?

Answer 1

Obviously, unreflect has a resolved method already, therefore doesn’t need to do a lookup. Also, it’s output depends on the Method you provide, a static method will yield a handle invoking the static method while findVirtual explicitly request a virtual method invocation. Keep in mind that MyClass.class.getMethod("myMethod", String.class, Map.class) might also find a static method accepting a String and a Map.

Further, if setAccessible(true) has been applied to the Method instance, you may get a handle accessing an otherwise inaccessible method which is not possible using findVirtual.

On the other hand, findVirtual may find appropriately typed invocations of the signature polymorphic methods MethodHandle.invoke and MethodHandle.invokeExact which can’t be accessed via java.lang.reflect.Method.