Fundamentals of JAVA and program operation

Brief introduction:

Originally designed for home appliances, because its features are just right for the internet, it has become a computer language, a platform, and a network computing architecture by rapidly becoming popular with applications on the Internet.

The Java language is an object-oriented programming language, and classes are the basic building blocks of Java programs, and all statements in Java appear in a class. Object-oriented includes two basic concepts: objects and classes.

Java is a simple, object-oriented, distributed, interpreted, secure, portable, and excellent performance language. It is a strong security, platform independence, hardware structure independence, Language concise, object-oriented features, in the Network programming language occupies an incomparable advantage, has become the realization of e-commerce systems, enterprise management platform, mobile device application development, such as the preferred language.

First, understand the birth process and version of Java:

Java was born with Sun company, the father of Java is James Gosling, officially born on May 23, 1952, Java's previous editions and features:

New features in Java SE 8

• Lambda expression
• Pipelines and streams
• Date and Time APIs
• Default method
• Type annotations
• Nashhorn JavaScript engine
• concurrency counters
• Parallel operation
• Remove PermGen Error
• TLS SNI

Java Version SE 7

The development Code is Dolphin (Dolphin), released in 2011-07-28.

The new features introduced include:

• A string is allowed as a branching condition in a switch statement block;
• Applying type inference when creating a generic object;
• Capturing multiple exceptions in a block of statements;
• Support Dynamic language;
• Support Try-with-resources;
• Introduction of Java nio.2 Development package;
• Numeric types can be represented by a 2-character string, and an underscore can be added to the string representation;
• Diamond type grammar;
• Automatic processing of NULL values.

Java Version SE 6

The development code is Mustang (Mustang), which was released in 2006-12-11.

The new features introduced include:

• Support scripting language;
• Introducing the JDBC 4.0 API;
• Introduction of Java Compiler API;
• pluggable annotations;
• Add the native PKI (public Key Infrastructure), Java GSS (Generic Security Service), Kerberos, and LDAP (lightweight Directory Access Protocol) support;
• Inherit Web Services;
• Do a lot of optimization.

Java Version SE 5.0

The development code was tiger, which was released in 2004-09-30.

The new features introduced include:

• introduction of generics;
• Enhance the loop, you can use the iterative mode;
• Automatic box packing and automatic unpacking;
• Type-Safe enumeration;
• variable parameters;
• static introduction;
• Meta data (annotations);
• Introduce instrumentation.

J2SE Version 1.4

The development code is Merlin (Hayabusa), released in 2004-02-06 (first issued under JCP).

The new features introduced include:

• XML processing;
• Java Print Service;
• introduction of logging API;
• Introduction of Java Web Start;
• Introducing the JDBC 3.0 API;
• introduction of assertions;
• Introduction of Preferences API;
• Introduction of chain-type exception handling;
• Support IPv6;
• supports regular expressions;
• Introduces the image I/O slot machine API.

J2SE Version 1.3

The development code is Kestrel (Red Falcon), released in 2000-05-08.

The new features introduced include:

• Introduction of Java Sound API;
• Jar file index;
• A lot of optimizations and enhancements have been made to all aspects of Java.

J2SE Version 1.2

The development code is playground (Playground), released in 1998-12-08.

The new features introduced include:

• Introduction of the Set (Collection) framework;
• Do memory mapping for string constants;
• Introducing the JIT (Just in time) compiler;
• Introduce the digital signature of packaged Java files;
• Introducing a policy tool to control authorization access to system resources;
• Introduction of JFC (Java Foundation Classes), including Swing 1.0, drag-and-drop and Java class library;
• Introduction of Java plug-ins;
• Introduction of scrollable result sets, blobs, CLOB, bulk updates, and user-defined types in JDBC;
• Add sound support to applets.

JDK Version 1.1

Issued in 1997-02-19.

The new features introduced include:

• Introduction of JDBC (Java Database Connectivity);
• Support for internal classes;
• Introducing Java Beans;
• Introduction of RMI (Remote Method invocation);
• Introduce reflection (for introspection only).

JDK Version 1.0

The development Code is Oak (oak), which was released in 1996-01-23.

Now what we have learned and what we are using is JAVA8.

There are two important concepts in Java, the JDK and the Jre:java core is the JDK,

Simply put, the JDK is a developer-oriented SDK that provides a Java development environment and a running environment. The SDK is software Development Kit generally refers to a software development package, which can include function libraries, compiler programs, and so on.
JDK is Java development Kit
The JRE is Java runtime enviroment, which refers to the Java Runtime Environment, and is intended for users of Java programs, not developers.
If the JDK is installed, there are two sets of JRE on your computer

The Java language is characterized by:

1, simplicity;

2, object-oriented,

3, platform-agnostic (once developed, run everywhere);

4, Health and safety;

5, multithreading (running multiple tasks at the same time).

Common Java is divided into three categories: Javase,javaee,javame, respectively.

1. Java SE (Java platform,standard Edition). Java SE was formerly known as J2SE. It allows you to develop and deploy Java applications that are used in desktops, servers, embedded environments, and live environments. Java SE contains classes that support Java WEB Service development and provides the foundation for Java platform,enterprise Edition (Java EE).

2. Java EE (Java platform,enterprise Edition). This version was formerly known as the Java EE. The Enterprise Edition helps develop and deploy portable, robust, scalable, and secure server-side Java applications. Built on the Java SE, Java EE provides Web services, component models, management, and communication APIs that can be used to implement enterprise-class service-oriented architecture (service-oriented Architecture,soa) and Web 2.0 applications.

3. Java ME (Java platform,micro Edition). This version 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, robust security model, many built-in network protocols, and rich support for Web and offline applications that can be dynamically downloaded. Applications based on the Java ME specification need to be written once, can be used for many devices, and can take advantage of the native capabilities of each device.

It's easier said than done.

Java SE is the software that runs on a computer.

Java EE is used to make Web sites-(our common JSP technology)

Java ME is a mobile phone software.

The Java program is run as follows:

There is an important concept in this process for Java virtual machines:

What is a Java virtual machine? Here is a description of it:

The Java Virtual machine (Java VM abbreviation JVM) is an abstract computer that runs all Java programs and is the operating environment of the Java language, which is one of the most attractive features of Java. It is essentially a software that is placed on an operating system, such as Unix,linux,windows, which provides a standard environment for running Java programs on a corresponding operating system. The reason we call this virtual machine is that we take this software as a virtual machine. The Java program we write runs on this virtual machine, isolating the specific operating system and hardware platform, thus realizing the platform independence of the Java program: programs developed on one operating system can run on any operating system. This is Java's "write Once, run everywhere". Different virtual machines are responsible for converting the same bytecode to the machine code that is applicable to the cost.

Fundamentals of JAVA and program operation