为什么子流程的输出顺序不对?

我有一个Java程序 sh 以交互模式作为子进程。输入是从 System.in 输出被复制到 System.out . 一切都很好,除了在运行诸如 pwd 在这个交互式shell中,输出以错误的顺序出现,例如:

$ pwd
$ /home/viz/workspace

而不是

$ pwd
/home/viz/workspace
$

区别在于在第一种情况下 $ 在输出之前打印 普华永道 .

你知道为什么会发生这种情况以及如何解决吗?

代码如下:

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

class StreamCopier implements Runnable {
    private InputStream in;
    private OutputStream out;

    public StreamCopier(InputStream in, OutputStream out) {
        this.in = in;
        this.out = out;
    }

    public void run() {
        try {
            int n;
            byte[] buffer = new byte[4096];
            while ((n = in.read(buffer)) != -1) {
                out.write(buffer, 0, n);
                out.flush();
            }
            out.close();
        }
        catch (IOException e) {
            System.out.println(e);
        }
    }
}

public class Test {
    public static void main(String[] args)
            throws IOException, InterruptedException {
        Process process = Runtime.getRuntime().exec("sh -i +m");
        Thread outThread = new Thread(new StreamCopier(
                process.getInputStream(), System.out));
        outThread.start();
        Thread errThread = new Thread(new StreamCopier(
                process.getErrorStream(), System.err));
        errThread.start();
        Thread inThread = new Thread(new StreamCopier(
                System.in, process.getOutputStream()));
        inThread.start();
        process.waitFor();
        outThread.join();
        errThread.join();
        inThread.join();
    }
}