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This article mainly introduces "what are the knowledge points related to Java objects". In the daily operation, I believe that many people have doubts about the knowledge points related to Java objects. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful for you to answer the questions about "what knowledge points related to Java objects?" Next, please follow the editor to study!

1. Object-oriented programming (Object-oriented Programming,OOP).

two。 The complexity of the problem to be solved depends directly on the type and quality of the abstraction.

3. Assembly language is a slight abstraction of the underlying machine; "imperative" language is an abstraction of assembly language, but the main abstraction done by this kind of language still requires that the problem be solved based on the structure of the computer. not based on the structure of the problem to be solved.

4.OOP allows the problem to be described by the problem, not by the computer on which the solution is running.

5.Alan Kay summarizes five basic features of Smalltalk, the first successful object-oriented language and one of the languages on which Java is based, which represent a purely object-oriented programming approach.

(1) all things are objects.

(2) programs are collections of objects that tell each other what to do by sending messages.

(3) each object has its own storage made up of other objects.

(4) each object has its own type

(5) all objects of a particular type can receive the same message.

6.Booch proposes a more concise description of objects: objects have state, behavior, and identity.

7. A class describes a collection of objects with the same properties (data elements) and behavior (function), and all a class is actually a data type.

8. Programmers can adapt to the problem by defining new classes according to their needs, that is, extending the programming language by adding new data types, and the programming system readily accepts new classes and takes care of them and type checking as if they were built-in classes.

Diagram in the form of 9.UML (Unified Modelling Language, Unified Modeling language): each class is represented by a box with the class name at the top of the box, the data members in the middle of the box, and the method at the bottom of the box. Typically, only the class name and public methods are shown in the UML design diagram. If you are only interested in the type, then the bottom of the box does not need to be given.

10. When trying to develop or understand a program design, one of the best ways is to think of an object as a "service provider". The program itself will provide services to the user, and it will do so by invoking services provided by other objects. Your goal is to create (or preferably look for in an existing code base) a series of objects that provide the ideal service to solve the problem.

11. Treating an object as a service provider helps to provide object cohesion. High cohesion is one of the basic quality requirements of software design: it means that all aspects of a software component are "well combined".

twelve。 In good object-oriented design, each object can accomplish a task well, but it doesn't try to do more.

13. Program developers are divided by role into class creators (programmers who create new data types) and client programmers (class consumers who use data types in their applications).

14. The goal of the class creator is to build the class, which exposes only the necessary parts to the client programmer, while hiding the other parts, and the hidden parts usually represent the fragile parts of the object, which can be easily destroyed by careless or ignorant client programmers. Hiding implementations can reduce the program bug; client programmers' goal is to collect a variety of classes for rapid application development.

15. The first reason for access control is to make it impossible for client programmers to touch parts that they should not touch; the second reason is to allow library designers to change the way classes work without worrying about affecting client programmers.

16. The easiest way to reuse a class is to use an object of that class directly. If you place it in a new class, it is called creating a member object in this class. This concept is called "composition" (has-a relationship), and if the composition is dynamic, it is called "aggregation".

17. Inheritance if only the methods of the base class are overridden, it means that the derived class (also known as the inherited class or subclass) and the base class (also known as the source class, superclass, or parent class) are of exactly the same type because they have exactly the same interface and can completely replace a base class object with a derived class object, which is considered a pure substitution, often referred to as the substitution principle, and the relationship between the base class and the derived class is * (is-a relationship). If a new method * * is added to the exported class, it is * * (is-like-a relationship) * *. The exported class extends the interface. Although the new type can still replace the base class, this substitution is not perfect because the base class cannot access the newly added method.

18. An object is not treated as a specific type to which it belongs, but as an object of the base class, which makes it possible to write code that does not depend on a specific type and is easy to extend, which is called generalization.

19. A function call generated by a non-object-oriented compiler causes so-called pre-binding, which means that the compiler generates a call to a specific function name, and the runtime resolves the call to the absolute address of the code to be executed. In OOP, with late binding, the compiler ensures the existence of the called method and performs type checking on the calling parameters and return values (languages that cannot provide such guarantees are called weakly typed languages), but do not know the exact code to be executed, and the program cannot determine the address of the code until run time. To perform late binding, Java replaces the absolute address call with a small piece of code that uses the information stored in the object to calculate the homemade of the method body.

20.Java is a single-root inheritance structure, all classes inherit from the Object class, and single-root inheritance ensures that all objects have certain functions, for example, all objects can be easily created on the heap and reclaimed by the garbage collector.

21.Craft + cannot ensure that all objects belong to the same basic type, which is better suited to the C model from a backward compatibility point of view and is less restrictive, but compatibility issues need to be addressed when referencing new class libraries (possibly through multiple inheritance).

In 22.Java, the container type holds a reference to the object in it, and the container can be expanded at any time. There are many types of containers, such as List (used to store sequences), Map (also known as associative arrays, used to establish associations between objects), Set (each object type holds only one), and artifacts such as queues, trees, stacks, and so on.

23.ArrayList and LinkedList can be understood as dynamic arrays and linked lists of objects. Their access characteristics and insertions and deletions are similar to arrays and linked lists. When you are not sure which one to use, the interface List of the two can be used to minimize the impact on the code when converting between containers.

24. Container + single-root inheritance structure means that the container that stores the Object type can store any type. When an object is placed in this container, the object reference is placed and transformed up to Object, and when it is retrieved, it gets a reference to the Object object, so it needs to be transformed down to its original type.

25. The upward transition is secure; the downward transition is not secure, and the solution is generics in Java.

26.Java dynamically creates objects in a memory pool called a heap until the runtime (the moment the relevant code is run) knows how many objects are needed, what their lifecycle is, and what the specific type is. If you need a new object, you can create it in the heap when needed, because the storage space is dynamically managed at run time, so it takes a lot of time to allocate storage space in the heap C++ implements the object in a combat or static storage area, and the storage space and declaration cycle of the object can be determined when programming. Creating storage space in the stack and releasing storage space usually require an assembly instruction to move the top pointer down and up, respectively. The former is relatively inefficient (the overhead is minimal when the program is complex) but convenient, while the latter is efficient but requires frequent consideration of memory leaks.

End. Noun popular science (from Baidu encyclopedia):

(1) LISP language (abbreviation of LISP,List Processing): founded in 1958, it is an early development and significant free software project. It is suitable for symbol processing, automatic reasoning, hardware description and VLSI design. The characteristic is that the table structure is used to express the non-numerical calculation problem, and the realization technology is simple. LISP has become the most influential and widely used artificial intelligence language.

(2) Prolog (Programming in logic): a logical programming language for deductive reasoning, it was first proposed by Colmeraner and his research team at the University of Marseilles in France in 1972.

(3) Smalltalk:Smalltalk is still considered to be the most representative and widely used object-oriented programming language. The predecessor of Smalltalk language is called Flex system, which was first proposed by Alan Kay. Smalltalk is easy to learn and easy to use, because its syntax and semantics are relatively simple, and there are not many concepts involved. A few concepts such as objects, classes, messages, and methods form the basis of Smalltalk programming.

(4) Booch:Booch method is one of the early object-oriented software development methods. Booch believes that software development is a spiral process, and each cycle includes four steps, namely, identifying classes and objects, determining the meaning of classes and objects, identifying relationships, and explaining the interface and implementation of each class. The development model of Booch method includes static model and dynamic model. Static model is divided into logical model (class diagram, object diagram) and physical model (module diagram, process diagram), which describes the composition and structure of the system. The dynamic model includes state diagram and sequence diagram.

(5) cohesion (Cohesion): also known as cohesion, is a software metric, which refers to the degree to which functional programs are combined into a module, or the state or degree of functional cohesion. It is one of the important concepts of structured analysis. There are many ways to measure cohesion. Some methods analyze the source code to get non-quantitative results, while others check the text characteristics of the source code to get the quantitative score of cohesion. Cohesion is a sequential measurement, which is generally expressed as "high cohesion" or "low cohesion". It is generally desired that the modules of the program have high cohesion, because high cohesion is generally related to many ideal software features, including robustness, reliability, reusability, and understandability (understandability), while low cohesion generally means that it is not easy to maintain, test, reuse and understand.

(6) robust is the transliteration of Robust, which means robust and strong. It is also the ability of the system to survive in abnormal and dangerous situations. For example, whether the computer software can not crash or crash in the case of input error, disk failure, network overload or intentional attack is the robustness of the software. The so-called "robustness" also means that the control system maintains some other performance characteristics under certain (structure, size) parameter perturbation. According to the different definitions of performance, it can be divided into stable robustness and performance robustness.

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