How can I execute linux terminal command from java?

Question

I want to automatically change the ip address of an Ubuntu 12.04 PC by a program fires at startup. For some certain reasons, I want to code it in Java.

Exactly the solution is written here:

Java - Execute a .SH file

But it does not work in my case. I could not manage to find why,essentially my case is a special case of so called thread, I try to run a sudo-command in linux with

public static void executeCommandLine(String strCommand){
    Runtime rt = Runtime.getRuntime();
    try {
        Process p = rt.exec(strCommand);
        if(p==null){
            System.out.println("Error in process");
        }
        BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

        String line = null;
         try {
            while ((line = reader.readLine()) != null)
             {
                System.out.println(line);
             }
        } catch (IOException e) {
            e.printStackTrace();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

I call this executeCommandLine() function from another function as follows:

public static void changeIpAddress(String strIpAddress, String strRootPassword, String strEthDevice){
    String strCommandLine = "";

    if(PLATFORM == PLATFORM_LINUX){
        strCommandLine =  "/bin/echo " + strRootPassword +  "| sudo -S /sbin/ifconfig " + strEthDevice + " " + strIpAddress;
    }else if(PLATFORM == PLATFORM_WINDOWS){
        // TODO: Write for Windows
    }else{
        System.out.println("OS not supported");
    }

    System.out.println("Executed command:");
    System.out.println(strCommandLine);

    executeCommandLine(strCommandLine);
}