Introduction to java

Java is a programming language, but now to a large extent, Java is no longer limited to a programming language, but has formed an idea. Java has a lot of supporters from its output to the present.

The development history of java

Java was developed using C++. Initially, Java was a support platform based on the GREEN project. When the GREEN project was born in 1991, the main purpose was to control the operation of all home appliances through Email. In fact, it is the Internet of Things that is hyped today. In fact, at least at that time: there were no smart devices, the Internet speed was very slow, and the popularity of the Internet was not very high. Including Email can only be regarded as an advertising platform today. The original sun engineers planned to use c++ to develop, but later considering the complexity of c++, they developed a set of OKA platform using c++. In the end, no one used OKA.

In the 1990s, Netscape went public in a short period of time. The company's product is the browser (FireFox), so SUN engineers began to learn browser technology from Netscape and launched the HotJava browser. So on the basis of HOtJava, in 1995, the Java programming language was launched.

SUN (Stanford University Network) is one of the earliest software companies. And Java is just its software product, but the company just caught up with the Internet slump that year. Acquired by Oracle in 2009.

Major versions of JDK (Java development Kit):

1995.05.23, JDK1.0, Java was officially launched;
1998.12.04, JDK1.2, Java was renamed Java2;
2005.05.23, JDK1.5, Java changed its name to Triger
The latest version now is JDK1.8.
The main feature is that it provides lamda expressions.

The initial development mode in Java is divided into three categories:

Java SE: (Before 2005, it became J2SE): For the development of stand-alone programs, it is often used as our basic platform.
Java ME: (Before 2005, it became J2ME): It was for mobile development, but it didn't catch up with the good times, and this development has since been replaced by Android.
Java EE: (Before 2005 became J2EE): is the enterprise version of Java development.

Key Features of Java

In the process of running the entire Java language, the core part is the JVM (that is, the Java Virtual Machine)

java is portable
Java language development is simple enough
Java is one of the few development languages for multithreaded programming
Java supports automatic garbage collection processing
Java is an object-oriented programming language

Java application running mechanism

Types of high-level computer programming languages:

compiled
interpretive

Hello.java---(compile)--->Hello.class---(interpretation 01010101011)--->Hello(java virtual machine)

Java Virtual Machine

A computer simulated by software or hardware on a computer. The Java virtual machine reads and processes compiled, platform-independent bytecode class files.
The Java compiler generates class files for the Java virtual machine and is therefore platform independent.
The Java interpreter is responsible for running the code on the Java virtual machine on a specific platform.

Java Virtual Machine

Java is a combination of two languages:

Compile command: javac.exe
Interpret command: java.exe

Java program composition:

Java source files
bytecode file
machine code instructions