toString() Method in Java

Print an object of your own class and you'll see something like Student@1b6d3586. That's the default toString() inherited from Object: the class name, an @, and the hash code in hex. It's correct but useless for a human. Overriding toString() gives your objects a readable text form, which makes printing, logging and debugging far easier.

Default vs Overridden

import java.util.Arrays;
import java.util.List;
 
public class Report {
    static class Student {
        private final String name;
        private final int marks;
 
        Student(String name, int marks) {
            this.name = name;
            this.marks = marks;
        }
 
        @Override
        public String toString() {
            return "Student[name=" + name + ", marks=" + marks + "]";
        }
    }
 
    public static void main(String[] args) {
        Student s = new Student("Advitha", 92);
        System.out.println(s);
        System.out.println("Topper: " + s);
 
        List<Student> list = List.of(s, new Student("Navika", 88));
        System.out.println(list);
 
        int[] scores = {92, 88, 75};
        System.out.println(Arrays.toString(scores));
    }
}

Student[name=Advitha, marks=92]
Topper: Student[name=Advitha, marks=92]
[Student[name=Advitha, marks=92], Student[name=Navika, marks=88]]
[92, 88, 75]

How it works

1. toString() is overridden to return the fields in a readable form. It must be public, because Object.toString() is public.
2. System.out.println(s) calls s.toString() for you.
3. String concatenation ("Topper: " + s) calls it too.
4. A List's own toString() calls toString() on each element.
5. Arrays don't override toString(). Printing scores directly would show something like [I@4e25154f; Arrays.toString gives [92, 88, 75].

Without the override, the first line would print something like this (the hex part changes from run to run):

Report$Student@1b6d3586

Where Java Calls toString()

Writing a Good toString()

• Include the fields that identify the object and help debugging.
• Leave out secrets: passwords, tokens, full card or Aadhaar numbers end up in logs.
• Keep it fast and free of side effects; debuggers call it often.
• Don't make other code parse it; it's for humans.

Common Mistakes

Printing an array directly. You get [I@.... Use Arrays.toString, or Arrays.deepToString for 2D arrays.

Writing public String tostring(). The lowercase s creates a new method; @Override would catch it.

Calling obj.toString() on a possibly null reference. It throws NullPointerException; String.valueOf(obj) or concatenation print null instead.

Interview Corner

Practice

1. Easy: Override toString() in a Book class with title, author and price, and print a book.
2. Harder: Override toString() in a BankAccount so it shows the holder and balance, but masks the account number to its last four digits, like XXXXXX4321.

Key Takeaways