How to write an array of objects to a File in Java?

Question

Suppose I have an object of class Student , which has the following fields:

String name;

int age;

int roll_number;

And I instantiate like so:

Student A[] = new Student();

Now, is there a way to store all this information in a text file using File Handling?

I thought about looping through each element in the array and then converting all the fields into Strings but that seems wrong.

Answer 1

Another way would be to use Serialization . Your Student class would have to implement Serializable :

class Student implements Serializable {

    private static final long serialVersionUID = 1L;

    private String name;
    private int age;
    private int rollNumber;
    //...
}

Then to read and write the Student array:

try {
    Student[] students = new Student[3];

    //Write Student array to file.
    FileOutputStream fos = new FileOutputStream("students.ser");
    ObjectOutputStream oos = new ObjectOutputStream(fos);
    oos.writeObject(students);
    oos.close();

    //Read Student array from file.
    FileInputStream fis = new FileInputStream("students.ser");
    ObjectInputStream ois = new ObjectInputStream(fis);
    Student[] studentsFromSavedFile = (Student[]) ois.readObject();
    ois.close();
}
catch (FileNotFoundException e) {
    e.printStackTrace();
}
catch (IOException e) {
    e.printStackTrace();
}
catch (ClassNotFoundException e) {
    e.printStackTrace();
}

Answer 2

You can always work out the format in your toString() method of the class so that when you do write to a file, it will write the object as per that format.

So lets say your toString() is,

public String toString() {
    return "Name : " + name + " : Age : " + age;
}

So this will write to your file as, (if you call bw.write(person.toString()); )

Name : Azhar : Age : 25

Answer 3

If you don't care of any format (text or binary), you can try a few ways:

1. Serialize them using Jackson to JSON or XML
2. Serialize then using Xstream to XML

Then you can store them to file using FileWriter