dos中的“ java”命令如何找到要使用的jre

Question

if one computer installed more than one jdk and jre, I want to know, when I excute "java" command in dos, how "java" command find which jre it should use? I saw a answer in somewhere, he said there there step to search jre:

1. search the current directory which java.exe placed to find the JRE directory

2. search the parent directory to find JRE directory

3. search the JRE directory based on the [HKEY_LOCAL_MACHINE\\SOFTWARE\\JavaSoft\\Java Runtime Environment] information in registry

It is right?

Answer 1

The Java command from a dos prompt is handled as any other dos command is.

That means it searches the PATH environment variable and the current folder.

If you want to run a specific version then use the full path to the version of Java you want to run.

If you want to always run a specific version then change your PATH environment variable accordingly.

The Java command will have come bundled with a particular JRE/JDK and will use that when executing.

Answer 2

When you execute java command, it depends on the PATH variable and the current directory. Java comes with bundled JRE which will be used. If you want to change to different version, then either need to change it in the PATH variable or execute it using the absolute path of java.exe.

Answer 3

When you write 'java' in the command line in windows, it will only do one thing:

Look if there is something called like that in your PATH , and call the first one that it finds.

Maybe you are asking about the java.exe stub that the JRE installation places in Windows/System32 (that is normally by default in the PATH ). That is not a full JRE, but a simple ad-hoc program which tries to do what you have described in your 3rd point.

Answer 4

As Marko Topolnik said, there is java.exe in \\windows\\system32, I test ,I delete the java.exe file in jdk bin folder, when I execute "java" command, it aslo can work, so it said that when execute "java" command in DOS, it actual execute java.exe in outer JRE bin folder, not the JDK bin java.exe. so I think the PATH didn't use for search JRE, is it right?