But from the compiler's perspective, why does Java enforce these rules? Improve this question. If the author had wanted you to be able to instantiate it, they could have made it non-abstract. The fact that they didn't -- even if they did implement all methods -- is a software architecture choice; they're telling you that they don't believe using the default implementation makes sense. Ask them why, or accept it and create a subclass. You can't do it because the author marked the class as abstract , and that is part of the meaning of the word in Java.
Because the Java language defines it so. Raymond Chenon In that answer, the abstract class is not instantiated. An anonymous subclass of the abstract class is instantiated. Add a comment.
Active Oldest Votes. Improve this answer. Eli Iser Eli Iser 2, 1 1 gold badge 19 19 silver badges 28 28 bronze badges. I agree. Some objects just do not exist, they are 'abstract' terms.
Taylor Taylor 3, 1 1 gold badge 18 18 silver badges 32 32 bronze badges. Thanks, I Guess its more like a rule, why it's because of the conceptual design, hence making compiler to force the error.
In addition to representing a concept that it makes no sense to instantiate like a 'vehicle' in the example given in this answer , it allows the program designer to specify things about that concept that are required, therefore assisting programmers that come afterward to understand and extend the Abstract class.
AFAIK, there is no requirement that any such concept, be an abstract class -- the 'vehicle' or whatever could be a superclass and allow instantiation, IF the program designer thought that was the best way to implement it. But the language designers allow you to do it this way. Vipul Verma Vipul Verma 1 1 silver badge 6 6 bronze badges.
An Abstract class does not require an Abstract method — cmd. Yes it does not. Was just using it to demonstrate. The OP is explicitly asking about an abstract class without an abstract method "even if it contains a Constructor and all methods are implemented" — Brian Roach.
Community Bot 1 1 1 silver badge. Then why prevent instantiation? Rudra21 Rudra21 3 3 silver badges 13 13 bronze badges. Ajay Kumar Ajay Kumar 3 3 silver badges 12 12 bronze badges. Ankita P. Assume compiler allow us to instantiate both ok. So if my method is not contains any body means how can jvm predict memory to allocate that method Second if no body means no method execution so never it will destroy from your Java stack area there may be a chance u can get memoryout error.
Bharti Rawat Bharti Rawat 1, 17 17 silver badges 31 31 bronze badges. I m not satisfied.. Private constructors are used in Singleton classes so as to avoid object creation from elsewhere — Reena Cyril.
Sonu patel Sonu patel 1 1 silver badge 8 8 bronze badges. You CAN instantiate an abstract class. You only need to provide a concrete subclass. Srinath Shah Srinath Shah 1 4 4 bronze badges. The sealed modifier prevents a class from being inherited and the abstract modifier requires a class to be inherited. A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.
Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation. For example:. The implementation is provided by a method override , which is a member of a non-abstract class. It is an error to use the static or virtual modifiers in an abstract method declaration.
Abstract properties behave like abstract methods, except for the differences in declaration and invocation syntax. An abstract inherited property can be overridden in a derived class by including a property declaration that uses the override modifier. An abstract class that implements an interface might map the interface methods onto abstract methods. In this example, the class DerivedClass is derived from an abstract class BaseClass.
The abstract class contains an abstract method, AbstractMethod , and two abstract properties, X and Y. However, if it does not, then the subclass must also be declared abstract. Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.
With interfaces, all fields are automatically public, static, and final, and all methods that you declare or define as default methods are public. In addition, you can extend only one class, whether or not it is abstract, whereas you can implement any number of interfaces. By reading this list of interfaces, you can infer that an instance of HashMap regardless of the developer or company who implemented the class can be cloned, is serializable which means that it can be converted into a byte stream; see the section Serializable Objects , and has the functionality of a map.
Note that many software libraries use both abstract classes and interfaces; the HashMap class implements several interfaces and also extends the abstract class AbstractMap. In an object-oriented drawing application, you can draw circles, rectangles, lines, Bezier curves, and many other graphic objects. These objects all have certain states for example: position, orientation, line color, fill color and behaviors for example: moveTo, rotate, resize, draw in common.
Some of these states and behaviors are the same for all graphic objects for example: position, fill color, and moveTo. Others require different implementations for example, resize or draw.
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