does an abstract class need a constructor?
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Yes! Abstract classes can have constructors! Yes, when we define a class to be an Abstract Class it cannot be instantiated but that does not mean an Abstract class cannot have a constructor. Each abstract class must have a concrete subclass which will implement the abstract methods of that abstract class.
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Which among the following can be used in place of default constructor? Explanation: For a parameterized constructor to be used as a default constructor, it must have all the default arguments. This makes the constructor to have optional arguments which are not mandatory to be passed.
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The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.
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The abstract keyword enables you to create classes and class members that are incomplete and must be implemented in a derived class. The sealed keyword enables you to prevent the inheritance of a class or certain class members that were previously marked virtual.
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A Java class can implement multiple interfaces but it can extend only one abstract class. 7. Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists.
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Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior. Variables declared in a Java interface is by default final. An abstract class may contain non-final variables.
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Virtual methods have an implementation and provide the derived classes with the option of overriding it. Abstract methods do not provide an implementation and force the derived classes to override the method. So, abstract methods have no actual code in them, and subclasses HAVE TO override the method.
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The differences it highlights are the accessibility of data members and methods: abstract classes allow non-static and non-final fields and allow methods to be public, private, or protected while interfaces' fields are inherently public, static, and final, and all interface methods are inherently public.
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Implicitly-typed variables must be initialized at the time of declaration; otherwise C# compiler would give an error: Implicitly-typed variables must be initialized.
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The key technical differences between an abstract class and an interface are: Abstract classes can have constants, members, method stubs (methods without a body) and defined methods, whereas interfaces can only have constants and methods stubs. ... This is because interfaces cannot define any implementation.
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We've seen that field-based injection should be avoided whenever possible due to its many drawbacks however elegant it may seem. ... Constructor-based injection is recommended for required dependencies allowing them to be immutable and preventing them to be null.
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Default constructor is also known as zero argument constructors. Default constructor does not have any parameters and is used to set (initialize) class data members. Since, there is no argument used in it, it is called "Zero Argument Constructor".
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Each implementation of Iterator is unique to the collection it is iterating. These is not enough common code to warrant an abstract base class. ... This combination allows for complete freedom to implement the interface but allows for code reuse in the cases where implementations can use the abstract class.
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An abstract class is a class that is declared abstract —it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.
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The instance constructor is executed each time you create an object (instance) with the CREATE OBJECT statement, while the class constructor is executed exactly once before you first access a class. The constructors are always present. ... An instance constructor can have IMPORTING parameters and exceptions.
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The purpose of constructor is to initialize the object of a class while the purpose of a method is to perform a task by executing java code. Constructors cannot be abstract, final, static and synchronised while methods can be. Constructors do not have return types while methods do.
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These two are quite different: Default methods are to add external functionality to existing classes without changing their state. And abstract classes are a normal type of inheritance, they are normal classes which are intended to be extended.