Basic concepts of Java (1) What is Java and java?

Basic concepts of Java (1) What is Java and java?
What is JavaJava? A development language (core feature: cross-platform, object-oriented, the name is here: what does 2 in J2EE mean). For developers, Java is basically equal to Jdk. Jdk version introduction here: Java developers usually write and compile Java code through IDE (Eclipse, NetBeans, JBuilder, etc.) (in the era of no IDE in ancient times, all are written in a text editor and compiled using javac). In this process, Jdk and third-party Jar packages are used (Jar packages are compressed by a set of compiled classes, you can use the decompression tool to decompress the package into a file structure ).
Do you want to know what Java can do? What can Java do? specific relationship diagram: Jdk contains Jre, and there is a directory named jre under the Jdk installation directory, there are two folders bin and lib. Here we can think that the bin is Jvm, And the lib is the class library required for Jvm work. The Jvm and lib are called Jre together. JdkJava Development Kit is a product for Java developers and is the core of Java. To install Jdk, see here: how to install and configure Jdk
Including: Java Runtime Environment Jre, Java tool (javac/java/jdb, etc.) and Java basic class library (Java API, rt. jar, etc ). 2. What is JreJava Runtime Environment?
Is a collection of environments required to run Java programs, including Jvm standard implementation and Java core class libraries.
Different from the well-known Jdk, Jre is a Java Runtime Environment, not a development environment, so it does not contain any development tools (such as compilers and debuggers ), only for users who use Java programs, Java developers can publish their own programs to users for use. To run Java programs, you must install Jre on your computer. Without jre, java programs cannot run. Without java programs, jre is useless. Including: Virtual Machine Jvm, runtime class libraries, and Java application launcher ). 3. What is JvmJava Virtual Machine?
The Java virtual machine is the core of cross-platform Java implementation and can run applications written in Java.
All Java programs are first compiled. the Jvm virtual machine can execute this compiled class file. That is to say, the class does not directly correspond to the operating system of the machine, but indirectly interacts with the operating system through the Virtual Machine, the Virtual Machine interprets the program as the target code (different operating systems) and runs it on the local system.
Jvm shields information related to the specific operating system platform, so that Java programs can run on multiple platforms without modification only by generating the target code that runs on the Java Virtual Machine.
Only the Jvm cannot be executed as a class, because when interpreting the class, the Jvm needs to call the library lib required for the explanation, that is, the lib class library in the Jre. The separate Jvm has no effect.