1 history and features of Java

0.1 the development of Java two leaps in internet development

• Www
• Java

The advent of Java

• 1990 Sun "Green"--development of home appliance software
• 1994 Oka Language
• 1995, Java language

Sun announces first version of compiler JDK1.0

Sun:stanford University Network

1.1 Java history and development Java is divided into three main platforms

• Java SE Standards Edition (J2se,java 2 Platform standard Edition)
• Java EE Enterprise Edition (J2ee,java 2 Platform, Enterprise Edition)
• Java ME Mini Version (J2me,java 2 Platform micro Edition)

The Standard Edition is suitable for desktop applications , the Enterprise Edition is suitable for Web applications , and the mini version is suitable for mobile applications .

Java Development Toolkit JDK (Java Development Kit)

1.2 Java language Features Java first is a programming language

• It is an object-oriented programming language (OOP)
• Its grammatical structure is very similar to the C and C + + languages
• The syntax used in Java is very simple

Rich Library of Classes

• Java provides a number of classes to meet the needs of networked, multithreaded, object-oriented systems
• Language Pack (Package)
• Utility Package
• I/O Package
• Network Package
• Graphical User Interface Pack
• And more ...

Java is c++--

• No direct pointer operation
• Automatic memory management
• Data type length fixed
• No header files
• Does not contain structures and unions
• Macros are not supported
• No multiple inheritance
• No class outside global variables
• No goto

What Java can do

• Object-oriented application development
• Development of various types of Web applications
• Visualization of the computational process
• Motion Picture/Interactive operation
• System Management for the Internet
• Database operations
• And more ...

1.3 Java Three core mechanisms of Java operating mechanism

• Java Virtual machine (Java VM)
• Code Security Detection
• garbage collection mechanism (garbage collection)

Compilation and operation of Java programs

Java Virtual machine (Java VM)

A computer that is emulated by software or hardware on a single computer.

The Java Virtual machine (JVM) reads and processes the compiled byte-code class file.

The Java Virtual Machine specification defines:
Instruction Set
Register set
class file Structure
Stack
Garbage collection Heap
Memory Area

Java Runtime Environment (JRE)

• JRE (the Java Runtime environment)
• JRE = JVM + API (LIB)
• The three main functions of the JRE when running the program:

Loading code: Completed by class loader;
Check code: completed by Bytecodeverifier;
Execution code: completed by runtime interpreter.

• Understand

Why Java is a cross-platform
Why Java is safe

Java Automatic garbage collection technology

• Garbage collection (garbage collection)
• In languages such as C + +, the programmer is responsible for recovering useless memory
• Java language Automatic garbage collection

System-level thread tracking allocation of storage space
Check and release the memory space that can be freed when the JVM is idle
Programmers do not have to control and interfere with the recycling process accurately.

JDK (Java Development Kit)

• Jdk=jre+tools
• Jre=jvm+api

Tools provided by the JDK

• java compiler Javac.exe
• Java Actuator Java.exe
• Document Builder Javadoc.exe
• Java Packager Jar.exe
• Java Debugger Jdb.exe

(This page is excerpted from: https://www.icourse163.org/learn/PKU-1001941004?tid=1002731007#/learn/content?type=detail&id= 1003758018&cid=1004476040)

1 history and features of Java