Jvm jre jdk. What are these things?

Source: Internet
Author: User

Jvm jre jdk. What are these things?

After installing JDK, we can imagine that we have bought a new computer with the software installed.

JVM: java Virtual Machine (Java Virtual Machine ). The so-called "Virtual Machine", as its name implies, is something simulated. It is like watching TV on a computer, but the computer does not have the same hardware support as in the TV, but we can still accept TV programs from the computer. That's because we have compiled a software program that can simulate the television hardware and run it on a computer platform. Similarly, the JVM simulates the computer hardware. It also has the ability to execute Code like a CPU. Its implementation includes: Instruction Set register group file format stack garbage collection heap memory zone. It can be understood as a machine dedicated to executing Java Program . That is to say, JVM provides a hardware platform for Java execution. The Code executed on JVM is stored in the
. Class file. JVM only executes bytecode files.

JRE: Java Runtime Environment (Java Runtime Environment ). Is the place where Java programs can be run. It is like running a video software on a computer must be on ipvs or Linux or other operating systems. Then we can regard it as an operating system. That is to say, JRE provides a Java execution software platform. In addition to JVM execution of Java code, Java APIs (Application Programming Interface, Application Programming Interface) are also required to run Java ". Java programs cannot run without these APIs, so JRE contains JVM.

JDK: Java Development Toolkit (Java Development Kit ). With the hardware and software platforms, we can do what we want to do. JDK is the tool we use to do things. It includes JRE and other tools. The version is different, that is, the tools in it are different. It's like you have different tools in different toolboxes. For example, the most common tool is javac, which translates. java files into. class files. Then let the JVM execute the bytecode in the. Class file. (Just like the computer's CPU only knows 0 or 1)

If a computer only needs to run a Java program, rather than writing a Java program, it only needs to install JRE. Now you know what these are about jvm jre jdk.

From: http://developer.51cto.com/art/200907/134918.htm

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