Запись в файл hashmap

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;


public class Test  {
	public static void main(String[] args) throws IOException {
		Map<Test2, Integer>hashmap = new HashMap<>();
		Map<Test2, Integer>hashma3 = new HashMap<>();
		Set<Test2>set = new HashSet<>();
		Test2 person1 = new Test2("Александр",1);
		Test2 person2 = new Test2("Александр",1);
		hashmap.put(person1, 1223);
		hashmap.put(person2, 123);
		
		set.add(person1);
		set.add(person2);
		hashma3.put(person1, 12);
		System.out.println(hashmap);
		System.out.println(set);
		{
	        File file = new File("temp.txt");
	        FileOutputStream f = new FileOutputStream(file);
	        ObjectOutputStream s = new ObjectOutputStream(f);
	        s.writeObject(hashmap);
	        s.close();
	    }
	}
	
}

package Forest;
import java.io.Serializable;
public class Test2 implements Serializable {
	
	private String name;
	private int id;
	
	public Test2 (String name, int id) {
		this.name = name;
		this.id = id;
	}
	public String toString() {
		return "Имя сотрудника "+ name+" ID сотрудика "+ id;
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Test2 other = (Test2) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
	
}