When dealing with abstract classes in Java it is not possible to create an object of that class.  So this would not work AbstractClassName object = new AbstractClassName();.  Why this is working AbstractClassName object = new NonAbstractClassName(); ?   Can you tell me what am I doing by using a constructor from a non abstract class (that extends the abstract one) and assign the object to a abstract class type?
685
I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this?   I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly.   Is it just so if you were to do:  IInterface classRef = new ObjectWhatever()   You could use any class that implements IInterface? When would you need to do that? The only thing I can think of is if you have a method and you are unsure of what object will be passed except for it implementing IInterface. I cannot think how often you would need to do that.   Also, how could you write a method that takes in an object that implements an interface? Is that possible?
32981
Is it possible to instantiate an object at runtime if I only have the DLL name and the class name, without adding a reference to the assembly in the project? The class implements a interface, so once I instantiate the class, I will then cast it to the interface.  Assembly name:     library.dll    Type name:      Company.Project.Classname     EDIT: I dont have the absolute path of the DLL, so Assembly.LoadFile won't work. The DLL might be in the application root, system32, or even loaded in the GAC.
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Let's say I have a class that has a member called data which is a list.    I want to be able to initialize the class with, for example, a filename (which contains data to initialize the list) or with an actual list.  What's your technique for doing this?  Do you just check the type by looking at __class__?  Is there some trick I might be missing?  I'm used to C++ where overloading by argument type is easy.
26254
The question is in Java why can't I define an abstract static method? for example  abstract class foo {     abstract void bar( ); // &lt;-- this is ok     abstract static void bar2(); //&lt;-- this isn't why? }
90347
How do i dynamically assign a name to a php object?  for example how would i assign a object to a var that is the id of the db row that i am using to create objects.  for example   $&lt;idnum&gt;= new object();   where idnum is the id from my database.
4097
Is it possible to call a constructor from another (within the same class, not from a subclass)? If yes how? And what could be the best way to call another constructor (if there are several ways to do it)?
85933
I was writing a toString() for a class in Java the other day by manually writing out each element of the class to a String and it occurred to me that using reflection it might be possible to create a generic toString() method that could work on ALL classes. I.E. it would figure out the field names and values and send them out to a String.  Getting the field names is fairly simple, here is what a co-worker came up with:  public static List initFieldArray(String className) throws ClassNotFoundException {      Class c = Class.forName(className);     Field field[] = c.getFields();     List&lt;String&gt; classFields = new ArrayList(field.length);      for (int i = 0; i &lt; field.length; i++) {         String cf = field[i].toString();         classFields.add(cf.substring(cf.lastIndexOf(".") + 1));     }      return classFields; }   Using a factory I could reduce the performance overhead by storing the fields once, the first time the toString() is called. However finding the values could be a lot more expensive.  Due to the performance of reflection this may be more hypothetical then practical. But I am interested in the idea of reflection and how I can use it to improve my everyday programming.
93507
In C#, is there a way to instantiate an instance of a class without invoking its constructor?  Assume the class is public and is defined in a 3rd party library and the constructor is internal.  The reasons I want to do this are complicated but it would be helpful to know if it's possible using some kind of C# hackery.  NOTE: I specifically do not want to call any constructor so using reflection to access the internal constructor is not an option.
89062
What is the meaning of "virtual" inheritance?  I saw the following code, and didn't understand the meaning of the keyword virtual in the following context:   class A {}; class B : public virtual A;
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Does anyone know why typedefs of class names don't work like class names for the friend declaration?  class A { public: };  class B : public A { public:    typedef A SUPERCLASS; };  typedef A X;  class C { public:    friend class A;             // OK    friend class X;             // fails    friend class B::SUPERCLASS; // fails };
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Why is it so hard to do this in Java? If you want to have any kind of module system you need to be able to load JAR files dynamically. I'm told there's a way of doing it by writing your own ClassLoader, but that's a lot of work for something that should (in my mind at least) be as easy as calling a method with a JAR file as its argument.  Any suggestions for simple code that does this?
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Is it possible to get the Type of an Object (it's not an SObject)?  String s = 'test'; doSomething(s);  public static void doSomething(o Object) {     // need to find out if o is a string or an integer     type = IsThereAMethodToGetTheTypeOf(o) // ?     if(type='String') {         // do something for strings here ....     } else {         // do something else ....     } }   I think the Type class can't help me, because it has no way to get the type of an existing object instance, right? Any there any other way?  Since there is most likely no perfect solution possible within the current platform limitations, I posted an Idea on IdeaExchange here:   For SObject I have already this  public static string getType(SObject obj) {     if(obj==null) return '';     return obj.getSObjectType().getDescribe().getName()+''; }
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I'm not sure if this is a strange thing to do or not, or if it is some how code smell...but I was wondering if there was a way (some sort of oop pattern would be nice) to "cast" a base type to a form of its derived type. I know this makes little sense as the derived type will have additional functionality that the parent doesn't offer which is in its self not fundamentally sound. But is there some way to do this? Here is a code example to so I can better explain what I"m asking.  public class SomeBaseClass {     public string GetBaseClassName {get;set;}     public bool BooleanEvaluator {get;set;} }  public class SomeDerivedClass : SomeBaseClass {     public void Insert(SqlConnection connection) {           //...random connection stuff           cmd.Parameters["IsItTrue"].Value = this.BooleanEvalutar;           //...     } }  public static void Main(object[] args) {     SomeBaseClass baseClass = new SomeBaseClass();     SomeDerivedClass derClass = (SomeDerivedClass)baseClass;      derClass.Insert(new sqlConnection()); }   I know this seems goofy but is there any way to accomplish something of this sort?
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I would like to use Class.newInstance() but the class I am instantiating does not have a nullary constructor. Therefore I need to be able to pass in constructor arguments. Is there a way to do this?
5309
How do I find out a name of class that created an instance of an object in Python if the function I am doing this from is the base class of which the class of the instance has been derived?  Was thinking maybe  might have helped me out here, but it doesn't seem to give me what I want. And short of parsing the __class__ member, I'm not sure how to get at this information.
929
I would like to be able to write a Java class in one package which can access non-public methods of a class in another package without having to make it a subclass of the other class. Is this possible?
58422
What are good reasons to prohibit inheritance in Java, for example by using final classes or classes using a single, private parameterless constructor? What are good reasons of making a method final?