Java beginners-basics, java beginners-

Java beginners-basics, java beginners-

1. java concepts

Java is a simple, object-oriented, distributed, interpreted, secure, portable, and multi-threaded language with excellent performance. With its strong security, platform independence, hardware structure independence, concise language, and object-oriented features, it boasts unparalleled advantages in network programming predictions, it is the preferred language for e-commerce systems, enterprise management platforms, and mobile device application development.

2. java Technical Features

Java technology can be divided into java programming language and java platform. Java programming language is a high-level programming language. Language Features: simple, structure neutral, object-oriented (java00) [Object-Oriented Programming (00 p)], distributed, portable, high-performance, multithreading, robust, dynamic, and secure.

3. java Development

The java2 Platform is divided into three major fields: J2SE-Standard Edition, which is mainly used for desktop application development and serves as the basis for J2EE. J2EE-Enterprise Edition is applicable to servers, focuses on enterprise-level distributed software systems. The j2s-microversion is mainly used for embedded devices that belong to a subset of J2SE, but supports special class libraries.

4. Basic java syntax

(1) java keywords: boolean, break, byte, abstract, case... (cannot be used as an identifier)

(2) java identifiers: rules followed by identifiers

(3) data types used by java: Basic Data Types (INTEGER: byte, int, short, long floating point type: float, double random type: char boolean type: boolean ), reference data type (class: class Interface: Interface array)

(4) java variables and constants: variables are used to store data and define constants.

(5) java operators and expressions

(6) java annotations

5. Program Process Control

Select and loop statements are called control structures. (Boolean logic, if/else statement, switch statement, for loop, while loop, do/while LOOP)

6. Classes, objects, and packages

Class: Classes in java are declared with keywords class. The java source code file can only contain-public class. The file name must be the same as the class name of the public class, and the file extension is ". java".

Object: in java, the new keyword is used to instantiate an object.

(1) Add member variables to the class (with default initial values)

(2) Add a method to the class

Class and object:

A class is the abstraction of an object, and an object is an instance of a class. Class [attribute (feature, static), method (behavior, dynamic)] is a combination of objects with the same attributes and behaviors.

Package: the package is used to organize classes. When declaring a package, the first line of the executable statement must be placed.

Fully Qualified name: pkg. test. pkgDemo