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java interview: Java Fundamentals section: 11 ? == equals
18？
22 : The purpose of encapsulation: to achieve high cohesion and low coupling within the software. Core: Put the methods and related methods that operate on the same thing into the same class, and put the methods and the data they operate into the same class.
Object-oriented encapsulation: Encapsulate the object into a highly autonomous and relatively closed individual, and the state of the object is read and changed by the behavior of the object.
Abstraction: Abstraction is about finding the similarities and commonalities of things and then grouping those things down into a class. This class only considers the similarities and commonalities of these foods.
Comprehension: Be good at dividing the boundary of the problem, and only consider what the system needs.
Inheritance: The mechanism by which subclasses automatically share data and methods of the parent class, which is a relationship between classes. Improve the reusability and scalability of the software.
Polymorphism: ? ? ? ? 22 23
24 : A class with abstract modification is an abstract class, and an abstract class cannot create instance objects. Abstract methods defined in abstract classes must be implemented in concrete ( Concrete ) subclasses. Therefore, there cannot be abstract constructors and abstract static methods. If the subclass does not implement all the abstract methods of the abstract superclass, the subclass must be defined as abstract type.
Interface ( interface ): It can be said to be a special case of an abstract class, all the methods in the interface are abstract. The methods in the interface default to the public abstract type. The member variables in the interface are public static final by default .
the difference:
1 : An abstract class can have a constructor, but an interface cannot have a constructor.
2 : There can be ordinary member variables in abstract classes, but there are no ordinary member variables in interfaces.
3 : An abstract class can contain non-abstract ordinary methods, all methods in an interface must be abstract, and there cannot be non-abstract ordinary methods.
4 : The access type of the abstract method in the abstract class can be public and protect , but the abstract method in the interface can only be public , and the default is public abstract .
5 : An abstract class can contain static methods, but an interface cannot contain static methods.