Java SE entry, JDK download and installation, first Java program, Java program compilation and execution

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Java SE:

Java SE: Java Standard Edition
Java me: Java mobile edition
Java EE: Java Enterprise Edition

Java was launched by Sun (acquired by Oracle earlier this year ).

Price: USD 7.4 billion

J2se, j2-and J2EE

JDK: Java Development Kit (essential for Java Development)
JRE: Java Runtime Environment (Java execution environment)

JDK contains JRE.

JDK 1.4, JDK 1.5 (5.0), JDK 1.6 (6.0)

JDK 1.5 (5.0): Tiger, tiger
JDK 1.6 (6.0): Mustang, Mustang

1. Download JDK
2. Install JDK
3. Set environment variables (User variables or system variables) and point to the JDK installation directory.
Bin directory
4. Run cmd to open the command line window, and enter Java-version to display the Java version.
Information

Next, you can write JavaProgram.

You can directly use Windows notepad to write Java programs, or use editplus and ultraedit
Advanced text editing tools such as Java programming, you can also use professional IDE (Integrated
Development Environment.

In the first lesson, we use NotePad to implement a hello World Java program.

All JavaCodeAnd its suffixes all end with Java.

Java program execution process is divided into two steps:
1. Compile
2. Run

The class file is a bytecode file, and the program will eventually execute this bytecode file.

Compile command: Java test. Java
Execute the command: Java test (note that there is no. class after test)

Java is a cross-platform language. It does not actually execute binary code, but bytecode.

JVM (Java virtual machine, Java Virtual Machine)

Java is cross-platform, while JVM is not cross-platform (JVM is written in C language)

The reason why Java can achieve cross-platform is that JVM is not cross-platform.