For loop to write data to file Java

you can use json format to save your data easily and orginized like this

public void saveWorksToFile(OutputStreamWriter writer) {
    // write your code here
    JSONObject jsonObject = new JSONObject();
    try {
        jsonObject.put("ARTIST_NAME",this.name);
        jsonObject.put("NUM_WORKS",this.works.size());
        for (int i=0;i<works.size();i++) {
            jsonObject.put("work_" + i, works.get(i).toString());
            // you can save work as a byte array or json string so you could easily import the data back
        }

        BufferedWriter buffer = new BufferedWriter(writer);
        buffer.write(jsonObject.toString()+"\n");
        buffer.close();
    }
    catch (IOException | JSONException e) {
        System.out.println("IOException occurred");
    }
}
public Artist readFromFile(File file){
    Artist artist = null;
    FileReader fileReader = null;
    String line= null;
    BufferedReader bufferedReader;
    try {
        fileReader = new FileReader(file);

        bufferedReader = new BufferedReader(fileReader);
        
        line = bufferedReader.readLine();


        while (line != null){
            line += "\n";

            JSONObject jsonObject  = null;
            try {
                jsonObject = new JSONObject(line);

                String name = jsonObject.get("ARTIST_NAME").toString();
                int works_num = Integer.parseInt(jsonObject.get("NUM_WORKS").toString());
                // here you can import the works as a string.


                artist = new Artist(name);


            } catch (JSONException e) {
                e.printStackTrace();
            }

            line = bufferedReader.readLine();

        }

        bufferedReader.close();

    } catch (IOException e) {
        e.printStackTrace();
    }
    return artist;
}

Below is my code for method saveWorksToFile. It is the only part of the code in your question that I changed. (Notes after the code.)

public void saveWorksToFile(Writer writer) {
    try {
        writer.write(this.name);
        writer.write(System.lineSeparator());
        writer.write("works: " + this.works.size());
        writer.write(System.lineSeparator());
        writer.write("---");
        writer.write(System.lineSeparator());
        boolean first = true;
        for (Work work : works) {
            if (first) {
                first = false;
            }
            else {
                writer.write(System.lineSeparator());
            }
            writer.write(work.toString());
        }
    }
    catch (IOException e) {
        System.out.println("IOException occurred");
    }
}

You are not meant to wrap the Writer parameter in a BufferedWriter. In general, for any method, you usually should not need to cast the parameter. Hence, in the above code, I use only the methods of class Writer. Also note that I do not close Writer since that should be left to the code that invoked method saveWorksToFile.

In order to write a line separator, I call method lineSeparator of class java.lang.System.

In order to print all the artist's works one per line, I use a loop.

In order to ensure that the last entry in the artist's list of works is written without a line separator, the first work is written without a line separator and every subsequent work is written with a preceding line separator.

Here is a method I wrote to test the above code. It uses class java.io.StringWriter which is a subclass of Writer since class Writer is abstract and has no public constructor. In general, you cannot instantiate an abstract class. You need to use a concrete subclass. I use StringWriter so as to be able to print its contents easily to the screen. You can use class java.io.FileWriter if you want to write to an actual file.

/**
 * import java.io.StringWriter
 */
public static void main(String[] args) {
    Artist artist = new Artist("Vincent van Gogh");
    StringWriter sw = new StringWriter();
    artist.saveWorksToFile(sw);
    System.out.print(sw);
    System.out.println();
    artist = new Artist("Claude Monet");
    Work work = new Work("Bridge over a Pond of Water Lilies", 1899, "Oil on canvas");
    artist.addWork(work);
    work = new Work("Impression, Sunrise", 1872, "Oil on canvas");
    artist.addWork(work);
    sw = new StringWriter();
    artist.saveWorksToFile(sw);
    System.out.print(sw);
    System.out.println();
    artist = new Artist("Henri Matisse");
    work = new Work("Woman with a Hat", 1905, "Oil on canvas");
    artist.addWork(work);
    sw = new StringWriter();
    artist.saveWorksToFile(sw);
    System.out.print(sw);
}

This is the output I got when I ran the above main method.

Vincent van Gogh
works: 0
---

Claude Monet
works: 2
---
Bridge over a Pond of Water Lilies|1899|Oil on canvas
Impression, Sunrise|1872|Oil on canvas
Henry Matisse
works: 1
---
Woman with a Hat|1905|Oil on canvas

My advice is that you separate classes, sometimes it is difficult to figure out problems. I separated them like this.

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;


public class Artist {

    private String name; // e.g. "Henri Matisse"
    private List<Work> works = new ArrayList<>();

    public Artist(String name) {
        this.name = name;
    }

    public void addWork(Work  work) {
        this.works.add(work);
    }

    public void saveWork(){
        try{
            BufferedWriter writer = new BufferedWriter(
                    new FileWriter("path where want to save"));
            writer.write(this.name);
            writer.newLine();
            writer.write("works: " + this.works.size());
            writer.newLine();

            this.works.forEach(work -> {
                try {
                    writer.write(work.name);
                    writer.newLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });

            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


}

public class Work {
    String name; // e.g. "Mona Lisa"
    int yearCreated; // e.g. 1506
    String medium; // e.g. "Oil on poplar panel"

    public Work(String name, int yearCreated, String medium) {
        this.name = name;
        this.yearCreated = yearCreated;
        this.medium = medium;
    }

    public String getName() { return name; }
    public int getYearCreated() { return yearCreated; }
    public String getMedium() { return medium; }



    @Override
    public String toString() {
        return name + "|" + yearCreated + "|" + medium;
    }
}



public class Main {
    public static void main(String[] args) {

        Work work1 = new Work("Fast1",2019,"ss");
        Work work2 = new Work("Fast2",2019,"ss");

        Artist artist = new Artist("Artist_Tom_Cruise");
        artist.addWork(work1);
        artist.addWork(work2);

        artist.saveWork();
    }
}