0
Is it true that Abstract class objects never have to be instantiated?
Wiki User
∙ 14y ago
Yes. An Abstract class cannot be instantiated.
Wiki User
∙ 14y ago
Add your answer:
Earn +20 pts
What are the differences between class and abstract class?
Below is the main difference between the 3 components:Concrete class - Provides implementation for all its methods & also for methods from extended abstract classes or implemented interfacesAbstract class - Does not provide implementation for one or more of its methodsInterface - Does not provide implementation for any of its methods
Abstract class can be private?
A class can either be default or public it can never be declared as private, so the question of abstract class at the file level does not arise. But an inner class can be declared private and abstract as well.
How constructor called?
You cannot invoke a constructor explicitly. It will get invoked implicitly when you call the new keyword on the class to create an object of the class. Ex: private ClassExample obj = new ClassExample(); here this new keyword usage on the ClassExample class will invoke the constructor of this class and create an object of that class.
What is purpose of abstraction in java?
Abstract keyword used for method declaration declares the methods without implementations. Abstract class in java have abstract methods that is not implemented in abstract class, but implemented in subclasses in java program. If the class in java program is not required to get instantiated than that class use the abstract keyword but this class rather is available for other classes to extend by other classes. Abstract keyword will be used in method declaration to declare that method without providing the implementation in that java program. In other words we can say that, it formally unfinished class as well as method, that marked with the help of keyword abstract. Defining abstract is a way of preventing someone from instantiating a class that is supposed to be extended first. In java program abstract class is deliberately missing similar to like an interface which will missing all method bodies in the program. Abstract class provides a way to extend an actual class. We will not use new on abstract classes but will use abstract references in the java program, that always point to objects of the class that extends an abstract class. In java program for practical use of an abstract class, we will define a non-abstract class that extends an abstract one. This will use any of the inherited non-abstract methods. Most of the time abstract class may extend another abstract class. In that condition it need not implement all in the non-abstract methods. An abstract keyword used both on classes and methods. In case of class declared with an abstract keyword may not be instantiated that is the only thing that abstract keyword doing.
Is it necessary to implement all the methods of abstract classes in derived class?
An Abstract class is a way to organize inheritance, sometimes it makes no since to implement every method in a class (i.e. a predator class), it may implement some to pass to its children but some methods cannot be implemented without knowing what the class will do (i.e. eat() in a Tiger class). Therefore, abstract classes are templates for future specific classes. A disadvantage is that abstract classes cannot be instantiated, but most of the time it is logical not to create a object of an abstract class. heloooooo
What are the differences between class and abstract class?
Below is the main difference between the 3 components:Concrete class - Provides implementation for all its methods & also for methods from extended abstract classes or implemented interfacesAbstract class - Does not provide implementation for one or more of its methodsInterface - Does not provide implementation for any of its methods
What is the purpose of declaring abstract method?
Abstract Class: The class which contains the common features of components of several classes, but cannot it be instantiated by itself. It represents an abstract concept for which there is no actual existing expression. For instance, "Vegetation" is an abstract class - there is no such real, real thing as generic vegetation. Instead, there are only instances of vegetation, such as mango tree and rose plant, which are types of vegetation, and share common characteristics, such as having leaves and stem in at least part of the lifecycle. SO in software engineering, an abstract class is a class in a nominative type system which is declared by the programmer, and which has the property that it contains members which are also members of some declared subtype. In many object oriented programming languages, abstract classes are known as abstract base classes, interfaces, traits, mixins, flavors, or roles. Note that these names refer to different language constructs which are (or may be) used to implement abstract types. We can also say that abstract class is : -- A class which is used only as an ancestor and is never instantiated. In other word a concrete definition will say that A type of class with pure virtual member functions and one or more methods that are declared but not implemented, that behaves as a base class but prohibits the instantiation of any members of that class. i.e. It has a complete interface but only a partial implementation It is used to take advantage of inheritance yet prohibiting the generation of objects that are not completely defined. Concrete subclasses of an abstract class are required to flesh out the implementation by overriding the abstract methods.
Abstract class can be private?
A class can either be default or public it can never be declared as private, so the question of abstract class at the file level does not arise. But an inner class can be declared private and abstract as well.
How constructor called?
You cannot invoke a constructor explicitly. It will get invoked implicitly when you call the new keyword on the class to create an object of the class. Ex: private ClassExample obj = new ClassExample(); here this new keyword usage on the ClassExample class will invoke the constructor of this class and create an object of that class.
What is purpose of abstraction in java?
Abstract keyword used for method declaration declares the methods without implementations. Abstract class in java have abstract methods that is not implemented in abstract class, but implemented in subclasses in java program. If the class in java program is not required to get instantiated than that class use the abstract keyword but this class rather is available for other classes to extend by other classes. Abstract keyword will be used in method declaration to declare that method without providing the implementation in that java program. In other words we can say that, it formally unfinished class as well as method, that marked with the help of keyword abstract. Defining abstract is a way of preventing someone from instantiating a class that is supposed to be extended first. In java program abstract class is deliberately missing similar to like an interface which will missing all method bodies in the program. Abstract class provides a way to extend an actual class. We will not use new on abstract classes but will use abstract references in the java program, that always point to objects of the class that extends an abstract class. In java program for practical use of an abstract class, we will define a non-abstract class that extends an abstract one. This will use any of the inherited non-abstract methods. Most of the time abstract class may extend another abstract class. In that condition it need not implement all in the non-abstract methods. An abstract keyword used both on classes and methods. In case of class declared with an abstract keyword may not be instantiated that is the only thing that abstract keyword doing.
Is it necessary to implement all the methods of abstract classes in derived class?
An Abstract class is a way to organize inheritance, sometimes it makes no since to implement every method in a class (i.e. a predator class), it may implement some to pass to its children but some methods cannot be implemented without knowing what the class will do (i.e. eat() in a Tiger class). Therefore, abstract classes are templates for future specific classes. A disadvantage is that abstract classes cannot be instantiated, but most of the time it is logical not to create a object of an abstract class. heloooooo
What is similarities between Abstract Class and Interface?
If a class has one abstract method ,the class has to be an abstract class.Methods can be implemented in abstract class.Whereas a interface is like a abstract class...the only difference being that the methods are never implemented in Interface.
What can be declared in an abstract class?
Abstract classes are to be extended until to a concrete class.Can have both abstract & non abstract methods.An Abstract class can not be instantiated.A non abstract class can be extended to an abstract class.If At least one abstract method present in a class then that class must be abstract.abstract & final modifiers can never be together.abstract classes can have both abstract methods & non abstract methods.
Why method inner classes can only access final variables from method?
I think the main reason is because the inner class may "outlive" the method in which it was created. If this happens, then the memory storing those variables would be lost and we would run into problems when trying to access them. If the variables are defined as final, then Java knows that those values will never change and it can move/copy them when the class is created.
Real time example for interface vs abstract class in java?
w.frnds........ I am just trying to an example of abstract class and interface class in real life . As these two ["interface class" is not a term in Java programming - just "interface"] classes [sic] are a concept of objest orientation so easy we can easily compare thhese with our real life . Suppose we have an abstract class called clark and an abstract method behabour of this abstract class ,which has no definition in abstract class. two other class security and receptionist inherits these clark class. So in thses two derived class there must has to be a defonation of behabour method,which depends on the derived class which types of behabour they will show........ So that is a real life example of Abstract class .Interface is also same as abstract class only the difference is it can't contain any implementation of any method in base class or super class. I think this is a sufficient example to understand abstract class and interface. [No, it is not sufficient.] If u have any doubt then u can contact me with this email id-rkmahanta26@gmail.com [Interfaces support multiple inheritance; classes do not. Interfaces contain only public members; classes do not have to. Interfaces do not have superclasses, except the implicit 'Object' supertype; they have superinterfaces. Nested interfaces are always static, never inner, unlike classes which can be inner classes. "u" is not an English pronoun. Use the tutorial and the JLS to understand interfaces and abstract classes, not this garbage answer.]
What is the difference between abstract class and static class?
Abstract ClassAn abstract class is an abstract data type (ADT) or abstract base class (ABC). It is a conceptual class. Unlike concrete classes which can serve as generic base classes for more specialised classes, ADTs can only be instantiated through derivation. For instance, circles, triangles and rectangles are all types of shape and all can therefore be derived from a shape base class. However you wouldn't want consumers instantiating a generic shape since it would be impossible to work with a shape without knowing what type of shape it actually was. Thus the shape class is an ideal candidate for an ADT. An ADT is simply a base class that has one or more pure-virtual methods. A pure-virtual method is similar to a virtual method except that the ADT need not provide any implementation for that method. Even if it does provide a generic implementation, all derivatives must override that method, even if only to call the generic base class method. This ensures that all derivatives provide their own specialised implementations. A derivative that does not provide an implementation for all the pure-virtual methods it inherits becomes an ADT itself. However any implementations that it does provide can subsequently be inherited by its derivatives (those methods effectively become virtual methods rather than a pure-virtual method). Only classes that provide or inherit a complete implementation of all pure-virtual methods can physically be instantiated.Going back to our shape class, the shape::draw() method is an ideal candidate for a pure-virtual function since it is impossible to draw a shape without knowing what type of shape it is. However, a circle class would be expected to know how to draw itself thus it can provide the specific implementation for drawing circles. Similarly, rectangles and triangles will provide their own specific implementations. This then makes it possible to store a collection of generic shapes and have them draw themselves without the need to know their actual type; as with all virtual methods, the derivatives behave according to their actual type.Static ClassA static class is simply a class that contains nothing but static members. Like an abstract base class you cannot instantiate a static class, but because the members are static they can be accessed without the need to instantiate an object of the class. Static classes are useful in that they provide global functionality without the need to declare global variables and external functions that operate upon those variables (the variables can effectively be hidden in the class, thus limiting their exposure). They can be likened to a singleton class insofar as there can only ever be one instance of each data member. However, a static class is instantiated at compile time and exists for the entire duration of a program, whereas a singleton can normally be created and destroyed at any time. In terms of memory consumption alone, a singleton is far more efficient than a static class, which is one of the reasons static classes are often frowned upon. Note that static classes have no need for any constructors, operators or destructors (they have no this pointer since there can never be any instances of the class), thus the compiler-generated default constructor, copy constructor, destructor and assignment operator must all be declared private. Some languages may do this automatically but in C++ (which has no concept of static classes) you must explicitly declare them as such.While static classes do have their uses, bear in mind that the point of having a class in the first place is in order to instantiate independent objects from the class. Thus the only time you should ever use a static class is when the class data members must exist for the entire duration of the program and you want to ensure there can only ever be one instance of those members. However, for memory efficiency alone, a singleton class would be the preferred method. Moreover, if some or all of the static methods are closely associated with a generic class, then it makes more sense to encapsulate those methods as static members of that generic class rather than as a completely separate static class.
What is abstraction in oops?
Abstraction means to describe with a term or a brief sentence that the audience can understand the entirety. In OOPS context, the program unit is an abstraction by itself. When we use the term "program", we sort of know what it is, yet don't know anything of the detail what it can and will do. Hence, any software element may be thought of as an abstraction in OOPS if you do not know the detail implementation!! The element may be small as a method, a property, a class, an interface, and up to the entire application/program itself.
