Basic Java Concepts

What is an environment variable?

Environment variables usually refer to the operating system, which specifies some of the parameters required for the operating system to run. Usually a series of key-value pairs .

The role of the PATH environment variable

Path environment variable is the operating system external command search route

What is an external command search path? For example, if you execute the ipconfig command under CMD, the configuration of the current computer card is displayed. When input ipconfig, the operating system will execute Ipconfig.exe (C:\Windows\System32), that is, when the XXX command is entered, the system will execute the corresponding EXE, in the path of the variable value in turn to find the EXE's storage path, can not find the prompt error.

The role of CLASSPATH environment variables

The CLASSPATH environment variable is a class file search path. The variable value of the CLASSPATH environment variable is a point, the point represents the current directory,

When executing the Java Hello command, the program looks for the Hello.class file in the current directory

What's inside the JDK? The directory is as follows

Bin folder: All the commands you need to use Java, such as

Javac: Compiling, translating the source code into code that the computer can understand

Include folder: A program that puts some C language

JRE folder: Java Runtime Environment

Lib folder: Package files required by Java

Src.zip:java JDK Part source file

What is a JRE?

The JRE is the Java Runtime Environment,java runtime environment, including the Java Virtual Machine (JVM), Java platform Core class files, and other supporting files.

What is a JVM?

The JVM is the abbreviation for Java Virtual machine, which is a computer that is virtualized by software.

Programmers write Java source files (. java), the compiler checks the source file for syntax errors, compiles a byte code (. Class) file without errors, and can run on any virtual machine. There are different virtual machines for different operating systems, and the virtual machine compiles the class file into code appropriate for the current operating system, which is then handed to the hardware for execution by the operating system. Two-time compilation

Basic Java Concepts