public class One {
    private final Object o = new Object();
    private final String s = (String) o;
}
-----
javap -c One:

public One();
  Code:
   0:	aload_0
   1:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   4:	aload_0
   5:	new	#2; //class java/lang/Object
   8:	dup
   9:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   12:	putfield	#3; //Field o:Ljava/lang/Object;
   15:	aload_0
   16:	aload_0
   17:	getfield	#3; //Field o:Ljava/lang/Object;
   20:	checkcast	#4; //class java/lang/String
   23:	putfield	#5; //Field s:Ljava/lang/String;
   26:	return

}

================================

public class Two {
    private final Object o = new Object();
    private final String s = String.class.cast(o);
}
-----
javap -c Two:

public Two();
  Code:
   0:	aload_0
   1:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   4:	aload_0
   5:	new	#2; //class java/lang/Object
   8:	dup
   9:	invokespecial	#1; //Method java/lang/Object."<init>":()V
   12:	putfield	#3; //Field o:Ljava/lang/Object;
   15:	aload_0
   16:	ldc_w	#4; //class java/lang/String
   19:	aload_0
   20:	getfield	#3; //Field o:Ljava/lang/Object;
   23:	invokevirtual	#5; //Method java/lang/Class.cast:(Ljava/lang/Object;)Ljava/lang/Object;
   26:	checkcast	#4; //class java/lang/String
   29:	putfield	#6; //Field s:Ljava/lang/String;
   32:	return

}