(1) Java SE Standard Edition
Java Standard Edition
Develop common desktop and business applications, including Java's core class libraries (collections, database connections, network programming, etc.).
The Java language was born in May 1995, and Java SE 13 was released in September 2019.
Commonly used packages in the Java language:
java.util contains a large number of tool classes and collection classes in Java, such as Arrays, List, Set, etc.
java.net contains classes and interfaces related to Java network programming.
java.io contains classes and interfaces related to Java input and output.
java.awt contains related classes and interfaces for building GUIs.
Description: GUI, Graphical User Interface Graphical User Interface
(2) Java EE Enterprise Edition
Java Enterprise Edition
Develop enterprise-level applications, including Servlet, JSP, JavaBean, JDBC, Web Service and other technologies
(3) Java ME Micro Edition
Java Micro Edition
Develop consumer electronics and embedded devices. This version also provides advanced Internet protocols such as HTTP, so that mobile phones can directly access all information on the Internet in the form of Client/Server (C/S), and provide efficient wireless communication.
Use the import keyword to import a class in a package: import package name. class name
If you need to use multiple classes in a package, you can use: import package name.* to import all classes under the package.
Features of the Java language
(A) simple
The Java language uses references instead of pointers and provides an automatic garbage collection mechanism, eliminating the need for programmers to manage memory issues.
(B) Purely object-oriented: realize the relationship between things through class and object description.
Support: single inheritance between classes, multiple inheritance between interfaces.
Supports the implementation mechanism between classes and interfaces (the keyword is implements)
(C) safety
There are no pointers, so the outside world cannot point to memory by forging pointers.
(D) Cross-platform
The Java language achieves cross-platform through the virtual machine JVM and bytecode, and does not rely on the operating system to interpret and execute Java programs.
Benefits: The same Java program can run on different operating systems. Different operating systems only need to install different versions of the Java virtual machine.
Description: Java virtual machine, JVM, Java Virtual Machine
The Java program is compiled into a bytecode file (*.class) by the Java compiler, and the Java interpreter in the JVM will translate the *.class file into a machine code file on the platform, and then execute the corresponding machine code file .
As long as Java programs are "written once, they can run everywhere".
(E) Support multithreading
Multiple tasks in the program can be executed concurrently, which significantly improves the execution efficiency of the program.
(F) Distribution
Java is a distributed language, which not only supports various levels of network connections , but also supports reliable streaming network connections (Stream) through the Socket class. Users can create distributed clients and servers, and in the process, the network becomes a distributed delivery vehicle for software applications.