First, what is the JDK http://java-mzd.iteye.com/blog/838514
JDK: Java Development ToolKit (Java Development Kit ) . JDK whole JAVA core, including the Java Runtime Environment ( Java Runtime Envirnment ), a bunch of Java tools ( javac / the Java / JDB , etc.) and Java -based class libraries (ie Java API include rt.jar).
JRE: Java Runtime Enviromental (java runtime environment ). That is, we say the JAVA platform, all Java programs have the JRE to run under. Including the JVM and JAVA core class libraries and support files. Compared with the JDK, it does not contain development tools - compiler, debugger and other tools.
JVM: Java Virtual Mechinal (JAVA virtual machine ) . JVM is JRE part, which is a fictional computer, is passed over the actual computer simulation of various computer-implemented functions. JVM has its own sound hardware architecture, such as processors, stacks, registers, etc., also has a corresponding instruction. JVM main job is to explain its own set of instructions (i.e., byte code) and mapped to the local CPU instruction set or the OS system call. Java is cross-platform, in fact, different operating systems use different JVM mapping rules, allowed nothing to do with the operating system, the completion of the cross-platform . JVM on top of Java source files are not concerned, but generated by the source file class file its concern ( class File ). Class file comprises a composition JVM instruction set, the symbol table as well as some assistance information.
Two, jdk tarball download http://download.csdn.net/detail/jji8877032/9151743
Three, JDK environment variable configuration
Use JDK need to configure a total of three environment variables: java_home, classpath and path (not case sensitive).
1、java_home
Right-click on "My Computer" and select "Properties", click on the "Advanced" tab, select "Environment Variables." Enter the following dialog box:
In the System Variables field, click the "New" button, the following dialog box:
Fill in the name of the variable java_home, fill in the value of the variable C: \ Users \ aaa \ Desktop \ jdk1.7.0_17 (JDK path, extract the compressed path after the package), and then click OK, so java_home variables configuration is complete.
2、classpath
classpath, variable value
;.% JAVA_HOME% \ lib; % JAVA_HOME% \ lib \ tools.jar ( represented by the current path to increase.).
3、path
path variable already exists in the system variables, to modify the path variables only need to select the path variable, you can click Edit. Add the following variable values:
%% the JAVA_HOME \ bin;%% the JAVA_HOME \ JRE \ bin. Suggested that the JDK bin on the front of the path of the original path. Because in% SystemRoot% \ system32 There is also a java.exe / javaw.exe, which is the Windows operating system that comes with JRE, if we do not use their own equipment, then he acquiesced in the JRE, you can use our own equipment of. If the JDK bin on the front, then the path will take precedence.
