Serialzable.java

class Student implements Serializable {
	private String name;
	private int mark;
	//if attribute contains transient, not save.
	transient private String city;
	
	public Student(String name, int mark, String city) {
		this.name = name;
		this.mark = mark;
		this.city = city;
	}

	@Override
	public String toString() {
		return "Student [name=" + name + ", mark=" + mark + "]";
	}
}
class Group implements Serializable {
	private ArrayList<Student> students;
	
	public Group() {
		students = new ArrayList<Student>();
	}
	public void add(Student s){
		students.add(s);
	}
	@Override
	public String toString() {
		return "Group [students=" + students + "]";
	}
}

//Create groups, save in binary file and retrieve from this file
	Group g = new Group();
	g.add(new Student("John", 10, "Barcelona"));
	g.add(new Student("Daniel", 5, "Madrid"));
		
	ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("group"));
	out.writeObject(g);
	out.close();
		
	Group g2;
	ObjectInputStream in = new ObjectInputStream(new FileInputStream("group"));
	g2 = (Group) in.readObject();
	in.close();
	System.out.println(g2);