Introduction to Java
What is Java
Java is an object-oriented programming language, which not only absorbs the various advantages of C++ language, but also abandons concepts such as multiple inheritance and pointers that are difficult to understand in C++. Therefore, the Java languageIt has two features: powerful and easy to use. As a representative of static object-oriented programming language, Java language implements object-oriented theory very well, allowing programmers to perform complex programming with elegant thinking.
Three major versions
Java SE (J2SE, Java 2 Platform Standard Edition, Standard Edition)
Java SE was formerly known as J2SE. It allows the development and deployment of Java applications used in desktops, servers, embedded environments, and real-time environments. Java SE contains classes that support the development of Java Web services and provides the foundation for Java EE and Java ME.
Java EE (J2EE, Java 2 Platform Enterprise Edition, Enterprise Edition)
Java EE was formerly known as J2EE. The enterprise version helps develop and deploy portable, robust, scalable and secure server-side Java applications. Java EE is built on the basis of Java SE. It provides Web services, component models, management and communication APIs, which can be used to implement enterprise-level service-oriented architecture (SOA) and Web2.0 applications . In February 2018, Eclipse announced that JavaEE was officially renamed JakartaEE
Java ME (J2ME, Java 2 Platform Micro Edition, micro version)
Java ME was formerly known as J2ME. Java ME provides a robust and flexible environment for applications running on mobile devices and embedded devices (such as mobile phones, PDAs, TV set-top boxes, and printers). Java ME includes a flexible user interface, a robust security model, many built-in network protocols, and rich support for networked and offline applications that can be downloaded dynamically. Applications based on the Java ME specification only need to be written once, and can be used for many devices, and can take advantage of the native functions of each device.
Java technology system
The figure below is the Java technology system diagram provided by Oracle's official website
The relationship between JVM, JRE and JDK
JVM
Java Virtual Machine is a Java virtual machine. Java programs need to run on a virtual machine. Different platforms have their own virtual machines, so the Java language can be cross-platform.
JRE
The Java Runtime Environment includes the core class libraries required by the Java virtual machine and Java programs. The core class library is mainly the java.lang package: it contains the system classes necessary for running Java programs, such as basic data types, basic mathematical functions, string processing, threads, exception handling classes, etc. The system loads this package by default
If you want to run a developed Java program, you only need to install JRE in your computer.
JDK
Java Development Kit is provided to Java developers to use, which contains Java development tools, including JRE. So after installing JDK, there is no need to install JRE separately. Among the development tools: compilation tool (javac.exe), packaging tool (jar.exe), etc.
JVM&JRE&JDK relationship diagram
