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Why would you declare a method to be abstract?
Simply speaking, declaring a class to be “abstract”, you are enforcing a “contract” for the child classes which inherit it, so it provides a good way to maintain the “contract”. If all an abstract does is declare abstract methods, you are correct, it’s a bit silly, and an interface would likely be superior.
Is it compulsory for a class which is declared as abstract to have at least one abstract method?
An abstract class is not required to have an abstract method in it. But any class that has an abstract method in it or that does not provide an implementation for any abstract methods declared in its superclasses or implemented interfaces must be declared as an abstract class.
Can abstract methods be defined?
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.
Can we declare a method abstract without making the whole class abstract?
And yes, you can declare abstract class without defining an abstract method in it. Once you declare a class abstract it indicates that the class is incomplete and, you cannot instantiate it.
How do you declare an abstract method?
To declare an abstract method, use this general form: abstract type method-name(parameter-list); As you can see, no method body is present. Any concrete class(i.e. class without abstract keyword) that extends an abstract class must override all the abstract methods of the class.
Can abstract class implement methods?
Abstract classes can also extend interfaces so they can implement some of their methods. But they can also leave some of the methods unimplemented so the subclass can implement them. If you leave an interface method unimplemented, there is not need to declare it abstract, it is already in the contract.
When abstract methods are used?
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.
Can we use abstract method in normal class?
A normal class(non-abstract class) cannot have abstract methods. An abstract class can not be instantiated, which means you are not allowed to create an object of it.
Can an abstract method have a body?
Abstract methods cannot have body. Abstract class can have static fields and static method, like other classes. An abstract class cannot be declared as final. If a class extends an abstract class, then it should define all the abstract methods (override) of the base abstract class.