Java Common class, abstract class, interface, object-oriented understanding

1. Object-Oriented Programming:

The language of object-oriented programming is not only Java, but also:

Simula 67 (the first object-oriented language, supports both single-inheritance and certain meanings of polymorphic and partial dynamic binding);

Smalltalk (the first language that supports dynamic typing, supports single inheritance, polymorphism, and dynamic binding);

EIFFEL (supports multi-inheritance, polymorphism and dynamic binding);

C + + (most of its class-based attributes inherit from Simula. Support multi-inheritance, polymorphism and partial dynamic binding);

C # (also supports single inheritance, with many similarities to Java and C + +, etc.);

Python ([? Pa?θ?n] is an interpreted, object-oriented, dynamic data type of high-level programming language); Ruby (developed by the Japanese, is an open source object-oriented programming server-side scripting language); Scala, a multi-paradigm (MULTI-PARADIGM) programming language, is designed to integrate the various features of object-oriented programming and functional programming. Running on a Java Virtual machine) Process orientedTypical representative of programming language: C language.

Whether object-oriented or process-oriented, is to abstract the real world, in order to solve the problem of the formation of the thinking system.

process-oriented means that when we consider a problem, we consider its implementation in a specific process (transactional process) as a unit:  

Object-oriented means that when we consider a problem, we consider its properties and methods in the object unit:

2. Java class:

Java classes encapsulate properties and methods, and everything depends on classes and objects to make calls. The inside is divided into ordinary classes, abstract classes and interfaces:

① Interface:

1, the interface defines methods and properties;

cannot have constructors, cannot instantiate,
Can inherit multiple interfaces and can be modified with an abstract
2.methods only declare, no method body;
3, the property defaults toPublic Static FIANL, and must have an initialization value;
4, Java8 can define a common method, you can also define an inner class in the interface, define the common method in the inner class ② abstract class:1, abstract class definition methods and properties;
can have a construction method and cannot be instantiated
2.abstract classes can inherit abstract classes, and can only inherit one;
Abstract classes can also inherit a common class;
3, you candefine common methods, but must have method body;
4.property can have no initialization value
③ General class:1, ordinary class can inherit ordinary class,
and can only inheritan ordinary class;
2.ordinary classes can be inherited by abstract classes;
3, Ordinary class cansimultaneous implementation of multiple interfaces

The basic syntax emphasizes understanding, and the latter requires a deep understanding of interface-oriented programming ideas. The small part will also be in the back of a separate article on the interface summary.

Java Common class, abstract class, interface, object-oriented understanding