invokevirtual | 易学教程

Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference

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问题 Basically this app is supposed to ask for your name, with an option to save, which when click, an alert dialog pops up and asks 'are you sure?', when yes is clicked, it should say 'welcome + whatever name put'. my problem is that the app keeps shutting down before it says welcome. I declared the string as userName and ran it without any function to the string, and it just said 'welcome, null'. but when i did userName=editText.getText().toString(); the app shut down immediately. Please HELP I

InvokeExact on the object, whose type is dynamically loaded by classloader

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问题 I have spend whole day on this problem. My problem is how to make an MethodHandle.invokeExact invocation on an instance, whose class type is dynamically loaded at program runtime. To make problem more clear, i show my sample code below: Class<?> expClass = new MyClassLoader().load(....) //expClass is AddSample.class which is subclass of BaseTemplate BaseTemplate obj = expClass.getConstructor(...) .newInstance(...); MethodHandle myMH = MethodHandles.lookup().findVirtual(expClass, methodName,..

Is there any reason for not invokevirtual and invokeinteface bytecode instruction into one? [duplicate]

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问题 This question already has answers here : What is the point of invokeinterface? (2 answers) Closed 3 years ago . Is there any reason for making the instruction to invoke non-static non-constructor method into two distinct instruction instead of one unified instruction, like invokeinstance ? Does it has anything to do with some random internal JVM mechanism or it's yet another horrific legacy issue? I know we have invokespecial because invoking constructor needs name ckecking, marking one other

InvokeExact on the object, whose type is dynamically loaded by classloader

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I have spend whole day on this problem. My problem is how to make an MethodHandle.invokeExact invocation on an instance, whose class type is dynamically loaded at program runtime. To make problem more clear, i show my sample code below: Class<?> expClass = new MyClassLoader().load(....) //expClass is AddSample.class which is subclass of BaseTemplate BaseTemplate obj = expClass.getConstructor(...) .newInstance(...); MethodHandle myMH = MethodHandles.lookup().findVirtual(expClass, methodName,..); System.out.println("Object type "+obj.getClass()); //Print AddSample // If obj is declared as