Two problems on running a program from another using Process class

Dear:

I met two problem when running a process using Process class.

My Java program called Program-A,  needs to run another Java program called Program-B as a sub-process. P-A needs to run P-B. My solution is to make P-A compily P-B and then runs the entry class file of P-B.  When running, P-A add "bin" directory of P-B into CLASSPATH variable to guarantee that "java" command can find the entry class of P-B under its "bin" directory. Then P-A use Process class to run the command "java -classpah ..."Main" to run P-B from Main.class.

The first problem occurs when updating CLASSPATH variable. We know that the value of CLASSPATH is a combination of several directory names that are separated by ";" under Windows, or separated by ":" under MacOS, or by another character under other OS'. My program need to run under different OS'. Is there an appropriate way to obtain the separating character of CLASSPATH variable from some system variable, so I don't need to detected the OS when updating CLASSPATH every time.

The second problem is about the execution of a .class file. The entry class of P-B is Main.class. P-A runs it using java command. But the command I used under MacOS can not work under Windows. The same case happens under Windows. The command I use under MacOS is:

                /* for macos.  This command does not work under Windows*/
            String[] cmd = {"java",  "Main", "0"};
            String[] env = {"CLASSPATH=" + strClsPath};
            Process ps = Runtime.getRuntime().exec(cmd, env, new File("ProgramB/bin/"));
         


The comnand under Windows is

  /*   for win os. This command does not work under MacOs. */
            String strCmd = "java \"-classpath\" \"" + strClsPath + "\" \"Main\" 0";
            Process ps = Runtime.getRuntime().exec(strCmd);

Does someone know the appropriate format of command that can be used under all OS'.

A further question is about the solution. Is there a better solution for P-A to run P-B?