instance | 易学教程

Python object deleting itself

阅读更多关于 Python object deleting itself

Why won't this work? I'm trying to make an instance of a class delete itself. >>> class A(): def kill(self): del self >>> a = A() >>> a.kill() >>> a <__main__.A instance at 0x01F23170> 'self' is only a reference to the object. 'del self' is deleting the 'self' reference from the local namespace of the kill function, instead of the actual object. To see this for yourself, look at what happens when these two functions are executed: >>> class A(): ... def kill_a(self): ... print self ... del self ... def kill_b(self): ... del self ... print self ... >>> a = A() >>> b = A() >>> a.kill_a() <__main_

Can a method be a decorator of another method of the same class?

阅读更多关于 Can a method be a decorator of another method of the same class?

问题 I have a class with a dull repeating pattern on their functions and I wanted to turn this pattern into a decorator. But the thing is that this decorator must access some attributes of the current instance, so I wanted to turn it into a method in this class. I'm having some problems with that. So, this is similar to what I want: class DullRepetitiveClass: def __init__(self, nicevariable): self.nicevariable = nicevariable def mydecorator(self, myfunction): def call(*args, **kwargs): print "Hi!

super.onCreate(savedInstanceState);

阅读更多关于 super.onCreate(savedInstanceState);

I have created an Android Application Project and in MainActivity.java > onCreate() it is calling super.onCreate(savedInstanceState) . As a beginner, can anyone explain what is the purpose of the above line? Every Activity you make is started through a sequence of method calls. onCreate() is the first of these calls. Each and every one of your Activities extends android.app.Activity either directly or by subclassing another subclass of Activity . In Java, when you inherit from a class, you can override its methods to run your own code in them. A very common example of this is the overriding of

Java instance variable declare and Initialize in two statements

阅读更多关于 Java instance variable declare and Initialize in two statements

问题 Hi I'm having problem with initialization in java, following code give me compile error called : expected instanceInt = 100; but already I have declared it. If these things relate with stack and heap stuff please explain with simple terms and I'm newbie to java and I have no advanced knowledge on those area public class Init { int instanceInt; instanceInt = 100; public static void main(String[] args) { int localInt; u = 9000; } } 回答1: You can't use statements in the middle of your class. It

Should I use “this” keyword when I want to refer to instance variables within a method?

阅读更多关于 Should I use “this” keyword when I want to refer to instance variables within a method?

问题 My teacher says that when I try to access an instance variable within a method I should always use the this keyword, otherwise I would perform a double search. A local scope search and then an instance scope search. Example: public class Test(){ int cont=0; public void Method(){ System.out.println(cont);//Should I use This.cont instead? } } I hope he is wrong, but I can't find any argument. 回答1: No, only use this when you have a name conflict such as when a method parameter has the same name

Python : Assert that variable is instance method?

阅读更多关于 Python : Assert that variable is instance method?

问题 How can one check if a variable is an instance method or not? I'm using python 2.5. Something like this: class Test: def method(self): pass assert is_instance_method(Test().method) 回答1: inspect.ismethod is what you want to find out if you definitely have a method, rather than just something you can call. import inspect def foo(): pass class Test(object): def method(self): pass print inspect.ismethod(foo) # False print inspect.ismethod(Test) # False print inspect.ismethod(Test.method) # True

What exactly is an instance in Java?

阅读更多关于 What exactly is an instance in Java?

What is the difference between an object, instance, and reference? They say that they have to create an instance to their application? What does that mean? Mark Byers An object and an instance are the same thing . Personally I prefer to use the word "instance" when referring to a specific object of a specific type, for example "an instance of type Foo". But when talking about objects in general I would say "objects" rather than "instances". A reference either refers to a specific object or else it can be a null reference. They say that they have to create an instance to their application. What

Comparing two instances of a class

阅读更多关于 Comparing two instances of a class

问题 I have a class like this public class TestData { public string Name {get;set;} public string type {get;set;} public List<string> Members = new List<string>(); public void AddMembers(string[] members) { Members.AddRange(members); } } I want to know if it is possible to directly compare to instances of this class to eachother and find out they are exactly the same? what is the mechanism? I am looking gor something like if(testData1 == testData2) //Do Something And if not, how to do so? 回答1: You

How to copy/create derived class instance from a pointer to a polymorphic base class?

阅读更多关于 How to copy/create derived class instance from a pointer to a polymorphic base class?

I have been struggling with this kind of problem for a long time, so I decided to ask here. class Base { virtual ~Base(); }; class Derived1 : public Base { ... }; class Derived2 : public Base { ... }; ... // Copies the instance of derived class pointed by the *base pointer Base* CreateCopy(Base* base); The method should return a dynamically created copy, or at least store the object on stack in some data structure to avoid "returning address of a temporary" problem. The naive approach to implement the above method would be using multiple typeid s or dynamic_cast s in a series of if-statements

When do instance variables get initialized and values assigned?

阅读更多关于 When do instance variables get initialized and values assigned?

问题 When doees the instance variable get initialized? Is it after the constructor block is done or before it? Consider this example: public abstract class Parent { public Parent(){ System.out.println("Parent Constructor"); init(); } public void init(){ System.out.println("parent Init()"); } } public class Child extends Parent { private Integer attribute1; private Integer attribute2 = null; public Child(){ super(); System.out.println("Child Constructor"); } public void init(){ System.out.println(