Java Abstract classes and abstract methods

The following describes the association between abstract classes and abstract methods:

Abstract classes are classes that cannot be instantiated using the new method, that is, classes without specific instance objects.

Abstract classes are similar to "templates" to create and modify new classes based on their formats. Objects cannot be directly created by abstract classes. They can only be derived from abstract classes to create objects. When a class is declared as an abstract class, the modifier abstract must be added before the class.

The member methods in the abstract class can include general methods and abstract methods. Abstract methods are modified with abstract. This method only declares the returned data type, method name, and required parameters. There is no method body. That is to say, abstract methods only need to be declared without implementation. When a method is an abstract method, it means that the method must be overwritten by the method of the quilt class. Otherwise, the method of its subclass is still abstract, and The subclass must be abstract, the statement is abstract.

Abstract classes do not necessarily contain abstract methods, but classes that contain abstract methods must be declared as abstract classes. Abstract classes do not have actual functions and can only be used to derive their subclasses. Abstract classes can contain constructor methods, but they cannot be declared as abstract.

Call abstract methods and non-abstract methods in abstract classes. If the methods are static, they are directly abstract classes. The method is fine. If it is not static, an inherited non-abstract class must be required, and then the non-abstract class instance is used to call the method.

Abstract classes can implement interfaces. Methods in interfaces can not be implemented in abstract classes. When a subclass inherits an abstract class and the subclass is not an abstract class, the subclass must implement both the abstract methods in the abstract class and the methods in the interface.

Abstract classes cannot be modified using final, that is, a class cannot be both a final class and an abstract class.

Conclusion: abstract cannot be used in parallel with private, static, final, or native to modify the same method.