When to use flush() in java?

Question

import java.io. * ;
public class Ser {

    public static void main(String args[]) {

        try {
            John myObj = new John(\"Sachin\", \"Cricket\");
              


        

Answer 1

1. You use flush() to clear the internal buffers(if any) and force write(i.e. flush) all the pending data in to the stream destination.
2. close() method is used to close the stream, once called, you can't use the stream any more.
3. No. You are reading "a John object from a file". An object of type John should have been previously serialized in to the file.
4. There are many alternatives to Java serialization such as XStream. See this SO answer for alternatives to serialization.