1. java introduction and java Introduction

1. java introduction and java Introduction

1. Father of java: James Gosling)

2. 1995 developed by SUM and 2009 acquired by Oracle

3. java platform version:

*J2SE:The standard version of Java is the basis of both.
*J2EE:Development that is commonly used on mobile phones has been replaced by Android and is basically not used now.
*J2EE:It is mainly used for B/S structure applications.

4. java features: cross-platform

Platform: refers to the Operating System (Windows, Linux, Mac)

Cross-platform: Java programs can run on any operating system.

Principle: to achieve cross-platform implementation, Java Virtual Machine (JVM) is required to rely on Java. (that is, as long as the corresponding Virtual Machine is installed on each platform, java programs can be compiled only once, instead of writing multiple versions based on different platforms)

 

5,JVM JRE JDKDescription

* JVM (Java Virtual Machine ):Java Virtual MachineJava programs must run on virtual machines. different platforms have their own virtual machines. Therefore, java can be used across platforms.

* JRE (Java Runtime Environment ):Java Runtime EnvironmentIs the core class library required by Java Virtual Machine and Java program. To run a developed Java program, you only need to install JRE on the computer.

* JDK (Java development Kit ):Java Development KitIs provided to Java developers, including java development tools and JRE. Therefore, if JDK is installed, you do not need to install JRE separately.

Development tools: compilation tool (javac.exe) Packaging tool (jar.exe) and so on

Roles and relationships of JDK, JRE, and JVM

JDK includes JRE and Development Kit

JRE includes the core class library and JVM

In general, to compile a java program, you only need to install JDK, including JRE and JVM.