Question

I am quite confused here. I am preparing to SCJP, I wrote a small recursive to check BufferedWriter memory allocations before|after flush() & close() methods. Please see below code block, I have just wrote my Desktop files into a text file.

import java.io.*;

public class Myexception{

    private static String lvl = "";
    static BufferedWriter bw;
    private static File source = new File("C:\\Users\\"+System.getProperty("user.name")+"\\Desktop\\New folder\\myTest.txt");

    public static void main(String[] args) throws IOException {

        Runtime rt = Runtime.getRuntime();

        System.out.println("Free memory before recursive: " + rt.freeMemory());

        bw = new BufferedWriter(new FileWriter(source));

        checkFiles(new File("C:\\Users\\"+System.getProperty("user.name")+"\\Desktop"), 0);

        System.out.println("Memory after recursive: " + rt.freeMemory());

        bw.flush();
        bw.close();
        lvl = null;

        System.out.println("Memory after clean up: " + rt.freeMemory());
    }
    static void checkFiles(File file, int level) throws IOException{

        if(!file.exists()){

            System.out.println("File doesnt exist: " + file.getName() + file.getPath());
            return;
        }

        for(String s:file.list()){

            if(new File(file.getPath() + "\\" +  s).isDirectory()){

                bw.newLine();
                bw.write(lvl + "Directory: " + s);

                lvl += " ";

                checkFiles(new File(file.getPath() + "\\" +  s), level+1);

            }else{

                bw.newLine();
                bw.write(lvl + "File: " + s);

            }
        }
    }
}

Output is fine but what I didnt understand, free memory before than flush() & close() is the same as after than flush() & close().Please see my output:

Free memory before recursive: 126150232
Memory after recursive: 104461304
Memory after clean up: 104461304

I have checked existing topics but I couldn`t find exact explanation. I was expecting I will have more free memory after bw.close().

Thank you

Answer 1

Memory is cleaned only after Garbage Collector has run. Until that you will not see any changes in memory consumption.