instance

i would like to ask the question when it would be advantageous to use static variables/methods or in the other case instance variables/methods in Java? I know that it depends on the certain case (like programming util-classes as static methods), but can we declare something like a general strategy? TheLostMind At novice level : Use instance variables when : Every variable has a different value for different object. E.g. name of student, roll number etc.. use static variables when : The value of the variable is independent of the objects (not unique for each object). E.g. number of students.

Is it possible to get all instances of a class by entering this class's name as a string? Something like this? var instances = Reflection.findClass("com.someone.MyClass").getInstances(); Any feedback is appreciated. Thanks. No, there's nothing like that available. If you hook into the debugging API you may be able to do it, but not when running "normally". I don't know of a way of doing this at runtime, but, if you are happy doing it 'offline', you can do the following: Take a heap dump Load the heap dump into Eclipse MAT Open an OQL pane, and enter a command such as select * from com.someone

Possible Duplicate: Is there a simple way of obtaining all object instances of a specific class in Java In java, is there any possible way to get all the instances of a certain class? You can use a Factory static initializer when you instantiate your class ( Singleton pattern ) and then add each generated instance in the factory constructor to a List ... Something like this : class MyObject { private static List instances = new ArrayList(); public static MyObject createMyObject() { MyObject o = new MyObject(); instances.add(new java.lang.ref.WeakReference(o)); return o; } public static List

Heres some sample code, class Base { private int val; Base() { val = lookup(); } public int lookup() { //Perform some lookup // int num = someLookup(); return 5; } public int value() { return val; } } class Derived extends Base { private int num = 10; public int lookup() { return num; } } class Test { public static void main(String args[]) { Derived d = new Derived(); System.out.println("d.value() returns " + d.value()); } } output: d.value() returns 0 // I expected 10 as lookup() is overridden, but not 0! can someone clarify this? The initialization of Derived 's instance variables has not

Why does NSClassFromString return nil ? As per the definition it has to return class name. How should I take care to rectify this problem? I need to instantiate a class from string and call the method, which is in the class, using the instance created. This is how my code looks like: id myclass = [[NSClassFromString(@"Class_from_String") alloc] init]; [myclass method_from_class]; But the method_from_class function is not being called, control is not going into it. And my code is error free. Any idea how to solve this in Objective-C? The Documentation for the function says : Return Value The

Is there any way to check if object is an instance of a class? Not an instance of a concrete class, but an instance of any class. I can check that an object is not a class, not a module, not a traceback etc., but I am interested in a simple solution. isinstance() is your friend here. It returns a boolean and can be used in the following ways to check types. if isinstance(obj, (int, long, float, complex)): print obj, "is a built-in number type" if isinstance(obj, MyClass): print obj, "is of type MyClass" Hope this helps. Have you tried isinstance() built in function? You could also look at