In the context of object-oriented programming, an abstract method is a method that has no implementation in the abstract class in which it is declared. Instead, subclasses of the abstract class must provide an implementation for the abstract method. As per the definition of an abstract method, the method that has no implementation should be declared as abstract.
Therefore, any method that has an implementation cannot be abstract. This is because the purpose of an abstract method is to provide a contract that subclasses must adhere to by providing their own implementation. If a method already has an implementation, there is no need for subclasses to provide their own implementation.
Furthermore, constructors cannot be declared as abstract because they are the methods responsible for instantiating an object. A constructor has an implementation that initializes the object’s instance variables and prepares it for use. It is not possible to have an abstract constructor since there must be a concrete implementation of the constructor to create an object.
Similarly, static methods cannot be abstract because they exist at the class level rather than at the object level. Their implementation is determined at the compilation time and as the name suggests, they are static in nature. They cannot be overridden by the subclass and hence, there is no need for an abstract implementation.
Any method that has an implementation cannot be declared abstract as the very definition of an abstract method requires it to be implemented by its subclasses. This includes constructors and static methods, which are also not abstractable due to their unique properties.
What are non abstract methods in Java?
In Java, non-abstract methods are methods that contain a complete definition and implementation and can be used directly in a class or object without any need for further definition. These methods are also referred to as concrete methods or regular methods.
Usually, non-abstract methods are defined with a method signature that includes the method name, return type, and parameter list. They can also include some logic and processing statements that are executed when the method is called. These methods are used to perform specific operations or functions on an object or class.
Non-abstract methods provide a more specific implementation that is tailored to the needs of a particular object or class. They can be inherited by subclasses and overridden if necessary to provide custom behavior. Moreover, non-abstract methods can be called directly from an object without any need for an interface or an abstract class.
In Java, non-abstract methods can be declared with any access modifiers like public, private, protected, or default. The access modifiers control the visibility of the method to the other classes and objects in the program.
Non-abstract methods also contribute to the polymorphism feature of Java. By declaring a method with the same name and signature in different classes, we can override the method to provide different functionality that suits each class’s needs. Subsequently, we can call the method on any object of the parent class, and the method would behave differently based on the runtime type of the object.
Non-Abstract methods in Java provide a way to encapsulate behavior and data related to a class or object and enforce proper coding standards for software development.
What is difference between abstract and non abstract method in Java?
In Java programming language, methods are a set of instructions that help us in carrying out specific tasks. Java methods can be categorized into two – abstract and non-abstract methods. The main difference between these two types of methods is that non-abstract methods have a specific implementation, whereas abstract methods have no implementation and must be overridden by the derived classes.
Non-abstract methods, as mentioned earlier, have an implementation that is written in the code. These methods are also known as concrete methods. When a non-abstract method is called, it runs the implementation within the method, and the desired functionality is achieved. Non-abstract methods are used when we want to provide a defined implementation to the code block, and when we do not want the method to be overridden by the derived classes.
On the other hand, abstract methods have no implementation, and only a method signature is declared with a keyword “abstract.” This implies that when a class has an abstract method, it is mandatory to declare that class as an abstract class. An abstract class is a blueprint for other classes that inherit from it, and it cannot be instantiated.
The implementation of an abstract method is provided by the derived classes. This makes abstract methods useful when we want to provide a generic format of a method, but the details of the implementation are left for the child classes to decide.
Another difference between non-abstract and abstract methods is that abstract methods cannot reside in a non-abstract class, whereas non-abstract methods can reside in both abstract and non-abstract classes. Additionally, when a class inherits from an abstract class, it must override all the abstract methods present in the abstract class; however, this is not mandatory for non-abstract methods.
Non-Abstract methods provide a specific implementation of the methods in the code, whereas abstract methods only provide a generic method signature that should be implemented by the derived classes. Non-abstract methods can reside in both abstract and non-abstract classes, whereas abstract methods can only reside in abstract classes.
When a class inherits from an abstract class, it must override all the abstract methods present in the abstract class; however, this is not mandatory for non-abstract methods.
Can a non-abstract method be overridden?
Yes, a non-abstract method can be overridden in a subclass. When a subclass extends a parent class, it inherits all the properties and methods of the parent class. The subclass can then modify the inherited methods to provide its own implementation. This process is known as method overriding.
Method overriding is a way to provide a different implementation for a method inherited from the parent class in the subclass. The method signature remains the same, but the implementation can be different. The overriding method in the subclass must have the same name, return type, and parameter list as the original method in the parent class.
To override a method in a subclass, the method in the parent class must not be declared final, as final methods cannot be overridden. The method in the parent class must also have the same visibility modifier (public, protected, or private) as the overriding method in the subclass.
When a method is called on an object of the subclass, the JVM first checks if the method is overridden in the subclass. If it is, the subclass method is executed instead of the parent class method. If it is not, the parent class method is executed.
Non-Abstract methods can be overridden in a subclass, allowing the subclass to provide its own implementation for a method inherited from the parent class. The key requirements for method overriding are that the method in the parent class must not be final and must have the same signature as the overriding method in the subclass.
What is the meaning of non-abstract?
The term “non-abstract” refers to something that is concrete or tangible in nature, rather than existing only as an idea or concept. In other words, a non-abstract object or concept can be directly observed, physically touched or manipulated, or is otherwise discernible by the senses.
For example, a tangible object like a car or a plant is a non-abstract entity that can be seen, felt, and interacted with in a physical sense. On the other hand, abstract concepts such as love or justice are intangible and exist primarily as ideas or emotions in a person’s mind.
In terms of thinking and communication, an abstract concept is often difficult to grasp and explain since it lacks a physical presence or manifestation. Non-abstract concepts, on the other hand, are more easily understood since they possess a clear physical representation or embodiment.
Non-Abstract refers to something that has a concrete, tangible existence, while abstract refers to an intangible or conceptual entity. Understanding the difference between these two types of concepts can help people communicate more clearly and effectively, especially in academic and professional settings.
Can there be any method without abstract class?
Yes, there can be methods without abstract classes. In fact, most programming languages allow for the creation of methods or functions outside of classes altogether. These standalone methods can be used to perform a specific task or operation and can be called by other parts of the program.
However, abstract classes can be useful in certain situations. An abstract class is a class that cannot be instantiated, but serves as a blueprint for other classes to inherit from. It can contain abstract methods, which are methods without implementation that must be defined in any class that inherits from it.
Using abstract classes can help enforce consistency and structure in a program. By defining a set of abstract methods, any class that inherits from the abstract class must implement those methods, ensuring that the overall program functions as intended. It also allows for easier maintenance and updates, as changes made to the abstract class are reflected in all classes that inherit from it.
While there can be methods without abstract classes, using abstract classes can be beneficial in certain situations.
Can we have a abstract class without any method?
Yes, we can have an abstract class without any method. In object-oriented programming, an abstract class is a class that cannot be instantiated on its own, but must be extended by a subclass. An abstract class can contain abstract methods or concrete methods, which the subclass can inherit, override or implement.
However, it is not mandatory for an abstract class to have any methods, abstract or concrete. An abstract class can be used as a base class for grouping related classes under a common umbrella, or for defining a contract or interface for a set of related classes.
For example, let’s say we have a set of animal classes, such as Dog, Cat, and Bird, each with their own unique behaviors and attributes. We could create an abstract class called Animal, which does not define any methods, but serves as a common base class for all the animal subclasses. The Animal class could have a set of properties such as Name, Age, and Species, which all the subclasses could inherit.
In this case, the purpose of the Animal class is to provide a common interface or contract for all the animal subclasses, without having to define any specific methods. The subclasses would then implement their specific behaviors and methods, which could be called through the Animal base class.
It is possible to have an abstract class without any method. However, the purpose of the abstract class should be clearly defined, and it should provide a useful interface or contract for the subclasses to implement.
Does every method in abstract class have to be abstract?
No, every method in abstract class does not have to be abstract. An abstract class can have both abstract methods and non-abstract methods. In fact, an abstract class can have any kind of method that a normal class can have. The purpose of making a method abstract is to force the subclass to provide an implementation for that method.
On the other hand, non-abstract methods in an abstract class provide a default implementation for the subclasses. Non-abstract methods can be called directly on the subclass without the need for the subclass to provide its own implementation. These methods are useful for code reuse and to provide a common functionality across all the subclasses.
An abstract class can have abstract methods, non-abstract methods, or a combination of both. The decision to make a method abstract depends on whether the method needs to be implemented by the subclass or not. If the method is not essential for the functionality of the subclass, it can be a non-abstract method.
However, if the method is required for the subclass to function properly, it should be an abstract method.
What happens if I will not provide an abstract method in abstract class and interface?
If you do not provide an abstract method in an abstract class or interface, it would mean that the class or interface does not provide a blueprint for how the methods in the class/subclasses should be implemented. Basically, an abstract class or interface defines certain methods and properties that need to be implemented by its subclasses, but if there are no abstract methods specified, then there would be nothing specific to be implemented.
In the case of an abstract class, it would mean that the class cannot be instantiated and can only be used as a superclass for other classes, which would be required to define the abstract method themselves. If there is no abstract method in the abstract class, then it would just behave like a regular class, and there would be no restriction on how its methods or properties are defined in subclasses.
Similarly, in the case of an interface, the lack of an abstract method would mean that the interface provides no specific functionality or behavior to be implemented by the classes that implement it. An interface defines certain methods that must be implemented by the classes that use it. But without any abstract methods, any class that implements the interface can define its behavior in any way it wants, which would defeat the purpose of using interfaces in the first place.
Failing to provide an abstract method in an abstract class or interface would mean that the class or interface would not serve its intended purpose, and would just behave like any other normal class or interface. Therefore, it is essential to ensure that abstract classes and interfaces contain the required abstract methods to ensure that the intended functionality and behavior are defined clearly.
Is abstract method mandatory?
In object-oriented programming, an abstract method is a type of method that is declared but doesn’t have any implementation. Instead, the implementation is left to the subclass to which the abstract method is defined. An abstract method is declared with the abstract keyword, and it has no method body.
Whether an abstract method is mandatory depends on the design of the application. In some cases, it’s necessary to define an abstract method for a superclass so that the subclasses can provide their own implementation. For example, imagine a shape class that has an abstract method called “calculateArea.”
The different shapes such as circle, square, and rectangle will implement the “calculateArea” method in their own unique way. Without the abstract method, the shape class would not be able to provide any implementation for the calculateArea method, and the subclasses would not have a method they could override.
In other cases, abstract methods may not be necessary or even beneficial. It’s important to remember that abstract methods are used to create a contract between the superclass and subclass. If that contract is not necessary, such as the case with a simple utility class, then abstract methods are not mandatory.
An abstract method is not mandatory in every class, but when it is essential for a subclass to provide its own implementation, it’s necessary to define an abstract method in the superclass. It’s important to carefully consider when to use abstract methods to ensure the design of the application is clear and effective.
Can we declare interface without abstract method?
In Java, an interface is a collection of abstract methods that specify the behavior that a particular class should possess. As the name suggests, an abstract method is a method without a body, which means that it only specifies the signature of the method but does not provide any implementation.
So, technically speaking, an interface without any abstract method doesn’t make sense, as interfaces are designed to define a set of rules or guidelines for a class to follow. If there are no methods to define what a class should do, then there is no point in having an interface.
That being said, Java 8 introduced a new feature called default methods, which allows interfaces to have a default implementation for a method. This means that if a class does not provide its implementation for the method defined in the interface, the default implementation in the interface will be used.
However, even with the use of default methods, it is still not recommended to declare an interface without any abstract method, as it defeats the purpose of an interface. Interfaces are meant to act as blueprints for classes to implement, and without any methods to define what a class should do, an interface is nothing but an empty shell.
Is it necessary to implement all methods of an interface and abstract class?
In Java, both interfaces and abstract classes provide a way to define a contract for classes to implement or extend. Interfaces define a set of method signatures that a class must implement, while abstract classes can also provide concrete implementations of methods along with abstract ones, which subclasses must implement.
Now coming to the question, it is not necessary to implement all the methods of an interface or an abstract class, but it depends on the context and the requirements of your program.
In the case of an interface, it is mandatory to implement all the methods in a class that implements the interface. If certain methods do not apply to the context of the implementing class, you can either throw an exception or return a default value. However, it is not considered a good practice to do so, as interfaces define a contract that a class should adhere to.
If a class does not implement all the methods of an interface, it cannot be used where the interface is expected, which may lead to unexpected behavior or errors at runtime.
Similarly, in the case of an abstract class, you are not required to provide an implementation of all its abstract methods in its subclasses, but you must implement them if they make sense in the context of the subclass. For example, if you have an abstract class that defines a method for drawing shapes, and you have two subclasses, Circle and Square.
If only Circle has an implementation for the draw() method, it may not make sense to implement it in the Square class. In such cases, you can either provide a default implementation in the abstract class or leave it as abstract, depending on your requirements.
While it is not mandatory to implement all the methods in an interface or an abstract class, it is recommended to do so to ensure their proper functioning and maintain the contract of the interface or abstract class. However, if you cannot implement certain methods, make sure to provide a sensible alternative or a justification for why it is not implemented.