does an abstract class have a constructor?
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Yes, Abstract Classes can have constructors ! Abstract class can have a constructor though it cannot be instantiated. But the constructor defined in an abstract class can be used for instantiation of concrete class of this abstract class.
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Answer: Yes, an abstract class can have a constructor, even though abstract class cannot be instantiated. An abstract class constructor c# code example will be explained. ... So, we need a constructor in abstract class to initialize database libraries.
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Which statement is true about a static nested class? You must have a reference to an instance of the enclosing class in order to instantiate it. It does not have access to nonstatic members of the enclosing class.
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Abstract classes cannot be instantiated, but they can be subclassed. ... Note: Methods in an interface (see the Interfaces section) that are not declared as default or static are implicitly abstract, so the abstract modifier is not used with interface methods.
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From Java 8, it can have default and static methods also. ... Type of variables: Abstract class can have final, non-final, static and non-static variables. Interface has only static and final variables. Implementation: Abstract class can provide the implementation of interface.
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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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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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Abstract class can define constructor. They are more structured and can have a state associated with them. While in contrast, default method can be implemented only in the terms of invoking other interface methods, with no reference to a particular implementation's state.
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Concrete class in Java. A concrete class is a class that has an implementation for all of its methods. They cannot have any unimplemented methods. It can also extend an abstract class or implement an interface as long as it implements all their methods. It is a complete class and can be instantiated.
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An abstract class can provide an implementation, i.e. (public, protected, private) method bodies. An interface can just declare public method signatures. ... Subclasses can only extend at most one abstract class, but can implement any number of interfaces.
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An abstract class is designed to be inherited by subclasses that either implement or override its methods. In other words, abstract classes are either partially implemented or not implemented at all. ... An abstract class can have constructors—this is one major difference between an abstract class and an interface.
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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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In Java, an abstract class can implement an interface, and not provide implementations of all of the interface's methods. It is the responsibility of the first concrete class that has that abstract class as an ancestor to implement all of the methods in the interface.
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Constructor will be automatically invoked when an object is created whereas method has to be called explicitly. Constructor needs to have the same name as that of the class whereas functions need not be the same. There is no return type given in a constructor signature (header).
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The main difference is the compiler won't let you instantiate an abstract class, while you could instantiate a base class (which may not make sense). Notice with the variable d we are guaranteed that the abstract methods have been overridden (otherwise the DerivedType class would have a compiler error).
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A class with one (or more) virtual pure functions is abstract, and it can't be used to create a new object, so it doesn't have a constructor.
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An abstract class is declared using abstract modifier. A concrete class is note declared using abstract modifier. An abstract class cannot be directly instantiated using the new keyword. A concrete class can be directly instantiated using the new keyword.