Java process builder架构问题

ProcessBuilder pb = new ProcessBuilder("nonexistent-command");
Process process = pb.start();
int exitCode = process.waitFor();
if (exitCode != 0) {
    System.err.println("Command failed with exit code: " + exitCode);
}

ProcessBuilder pb = new ProcessBuilder("ls", "-l");
Process process = pb.start();

BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
    System.out.println(line);
}

int exitCode = process.waitFor();

ProcessBuilder pb = new ProcessBuilder("echo", "$MY_VAR");
Map<String, String> env = pb.environment();
env.put("MY_VAR", "my_value");

Process process = pb.start();
int exitCode = process.waitFor();