为什么（int）MethodHandle.invokeExact缺少checkcast-instruction？

Question

I have created 2 simple classes for try Java MethodHandle -API:

public class Foo {
    private static int staticField;

    public static Object getStaticField() {
        return staticField;
    }
}

another class for invoke method Foo.getStaticField() in two ways - direct and using MethodHandle -API:

....
public static void methodHandleGetStaticField() throws Throwable {
    MethodHandle methodHandle = lookup.findStatic(Foo.class, "getStaticField", MethodType.methodType(int.class));
    int i = (int)methodHandle.invokeExact();
}

public static void directGetStaticField() {
    int i = (int)Foo.getStaticField();
}
....

I have decompiled class and saw that directGetStaticField method contains cast instructiona, but method methodHandleGetStaticField doesn't, though java.lang.invoke.MethodHandle.invokeExact() returns java.lang.Object .

public static void directGetStaticField();
descriptor: ()V
Code:
   0: invokestatic  #70    // Method ru/fj/methodhandle/Foo.getStaticField:()Ljava/lang/Object;
   3: checkcast     #33    // class java/lang/Integer
   6: invokevirtual #74    // Method java/lang/Integer.intValue:()I
   9: istore_0
  10: return

public static void methodHandleGetStaticField() throws java.lang.Throwable;
descriptor: ()V
Code:
   0: getstatic     #15    // Field lookup:Ljava/lang/invoke/MethodHandles$Lookup;
   3: ldc           #29    // class ru/fj/methodhandle/Foo
   5: ldc           #90    // String getStaticField
   7: getstatic     #32    // Field java/lang/Integer.TYPE:Ljava/lang/Class;
  10: invokestatic  #38    // Method java/lang/invoke/MethodType.methodType:(Ljava/lang/Class;)Ljava/lang/invoke/MethodType;
  13: invokevirtual #46    // Method java/lang/invoke/MethodHandles$Lookup.findStatic:(Ljava/lang/Class;Ljava/lang/String;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/MethodHandle;
  16: astore_0
  17: aload_0
  18: invokevirtual #52    // Method java/lang/invoke/MethodHandle.invokeExact:()I
  21: istore_1
  22: return

Could anyone explain it for me?

Answer 1

You can notice that invokeExact indeed returns an int from its descriptor ()I :

  18: invokevirtual #52    // Method java/lang/invoke/MethodHandle.invokeExact:()I

As a result, no casting is required.

The reason why it returns an int , not an Object , is that method invokeExact (as well as invoke ) in MethodHandle are treated specially, see the invokeExact API

Returns :

the signature-polymorphic result, statically represented using Object

and from the signature polymorphism :

... The unusual part is that the symbolic type descriptor is derived from the actual argument and return types, not from the method declaration.