How to configure Java environment variables and steps.

Right click on My Computer, select "Properties", select the "Advanced" tab, enter the environment variable settings, and set the following three environment variables:

(1) Set the path variable in the environment variable configuration so that we can run Java applications anywhere in the system, such as javac, java, javah, etc. This is where we need to be found The directory where JDK is installed. For example, our JDK is installed in the D:\jdk1.6.0 directory, then the D:\jdk1.6.0\bin directory is our commonly used Java applications. We need to put D:\jdk1.6.0 \bin This directory is added to the path environment variable.

Find the path variable in the system variables,Select->Edit; (There are already many variable values ​​in it, just add it at the front of the variable value D:\jdk1.6.0\bin; )

Variable name: Path

Variable value: D:\jdk1.6.0\bin;

（2） Setting the classpath environment variable in the environment variable configuration is to let the Java interpreter know where to find this class when we need to reference a class written by others when developing a Java program. Usually Sun provides us with some additional rich class packages, one is dt.jar and the other is tools.jar. Both jar packages are located in the D:\jdk1.6.0\lib directory, so usually we will put these Add two jar packages to our classpath environment variable set classpath=.;D:\jdk1.6.0\lib\tools.jar;D:\jdk1.6.0\lib\dt.jar.

Click in the System Environment Variables column ->New classpath

Variable name: classpath

Variable value : .;%JAVA_HOME%\lib\tools.jar;%JAVA_HOME%\lib\dt.jar; (Note that there is a "." at the beginning of CLASSPATH, indicating the current directory, so when we run java AClass, The system will first search for the AClass file in the current directory.);

(3) Set JAVA_HOME:

a in the environment variable configuration. For convenience of reference, for example, If the JDK is installed in the D:\jdk1.6.0 directory, set JAVA_HOME to this directory path. Then when you want to use this path in the future, you only need to enter %JAVA_HOME% to avoid entering a long path string for each reference;

b. Adopt the principle of normalization. When the JDK path changes, you only need to change the variable value of JAVA_HOME. Otherwise, you must change any document that uses an absolute path to reference the JDK directory. If it is not changed, If a certain program cannot find the JDK, the consequences are conceivable - system crash!

c. Some third-party software will reference the agreed JAVA_HOME variable, otherwise, you will not be able to function normally Use this software.

Click in the column of system environment variables->Create JAVA_HOME (JAVA_HOME points to the JDK installation path)

◆Variable name: JAVA_HOME
◆Variable Value: D:\jdk1.6.0

After the configuration is completed, you can write a simple Java program to test whether the J2SDK has been installed successfully:

public class HelloWorld{          public static void main(String[] args){              System.out.println("Hello world!");          }    }

Save the program as a file named HelloWorld.java documentation.

Open the command prompt (Start-Run-type "cmd") window, enter the directory where the HelloWorld.java document is located, and then Type the following command

javac HelloWorld.java

java HelloWorld

If HelloWorld is printed out, the installation is successful. If this sentence is not printed, carefully check whether the above configuration is correct before performing the above operations.

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