Java FAQ _01 Basic Concepts (001) _ What is Java

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1. What is Java

Java is a development language (core features: cross-platform, object-oriented, name from the look here: what the 2 in the Java EE meaning), for the developer to say, it basically equals the JDK.

Version of JDK see here: [Java has those versions][3]

Developers typically write and compile Java code through the IDE (Eclipse, NetBeans, JBuilder, etc.) (in an age when there is no IDE in the ancient world, written in a text editor, compiled with Javac), in this process, Use the tarball to the JDK and the third-party jar package (the jar package is a set of compiled classes of the compressed package, you can use the decompression tool to extract the file structure).
Want to know what Java can do: [Java can do][4]

[4]:

Specific diagram:

Where the JDK contains the JRE, in the JDK installation directory has a directory named JRE, there are two folders Bin and Lib, where it can be considered that the bin is the jvm,lib in the JVM is required to work the class library, and the JVM and Lib and up called the JRE.

2. What is a JDK

Java Development Kit, a product for Java developers, is the core of the entire java.

Want to install JDK see here: [How to install and configure JDK][5]

[5]:

Includes: Java Runtime Environment JRE, Java Tools (JAVAC/JAVA/JDB, etc.) and Java base Class library (Java Api,rt.jar, etc.).

3. What is the JRE

Java Runtime Environment is the set of environments required to run Java programs, including the JVM standard implementation and the Java Core Class library.

Unlike the familiar JDK, the JRE is a Java runtime environment, not a development environment, so there is no development tools (such as compilers and debuggers), but only for users of Java programs, only through it, Java developers can publish their own programs to the user's hands, Let the user use.
Running Java programs generally requires the user's computer to install the JRE, no Jre,java programs can not run, and without Java programs, the JRE is useless.

Includes: Virtual machine JVM, run class library (runtime class libraries) and launcher (Java Application Launcher).

4. What is a JVM

Java Virtual machine, which we often call Java VMS, is the most central part of the entire Java implementation across the platform, capable of running applications written in the Java language.

All Java programs are first compiled into a. class file, and the JVM virtual machine can execute this compiled class file, which means that class does not directly correspond to the machine's operating system, but instead interacts with the operating system indirectly by the virtual machine, which interprets the program as the target code (different operating systems) to the local system.

The JVM masks information related to the operating system platform, allowing Java programs to run without modification on multiple platforms by generating only the target code that runs on the Java virtual machine.
Only the JVM cannot be executed as class, because the JVM needs to invoke the class library lib, the Lib class library in the JRE, which is required to interpret the class, and the individual JVM has no effect.

Java FAQ _01 Basic Concepts (001) _ What is Java