Main.java

import java.io.*;

public class Main {
    public static void main(String[] args) {
        A a = new A(4);
        try (OutputStream os = new FileOutputStream("a");
             ObjectOutputStream oos = new ObjectOutputStream(os)) {
            oos.writeObject(a);
            os.write("hello".getBytes());
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(0);
        }
        try (InputStream is = new FileInputStream("a");
             ObjectInputStream ois = new ObjectInputStream(is)) {
            A a1 = (A) ois.readObject();
            System.out.println(a1.getA());
            byte[] buf = new byte[128];
            int read = is.read(buf);
            System.out.println(new String(buf, 0, read));
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    static class A implements Serializable {
        private int a;

        public A(int a) {
            this.a = a;
        }

        public int getA() {
            return a;
        }
    }
}