Java Java Data Structures Getting There Object Inheritance

I'm still confused on what toString() does

When you add an object to return under the toString() method this overrides what exactly? and Where?

2 Answers

Hi Carolina. The toString() method is part of the Object Class. As every class is a subclass of the Object class, any class inherits that method.

What does it do? Its aim is to give a string representation of an object (an instance of that class). The original toString() method returns:

getClass().getName() + '@' + Integer.toHexString(hashCode());

For example:

com.company.Dog@4554617c

where

  • com.company is the package
  • Dog is the class
  • 4554617c is the hash code converted into hex String. The hash code is an Integer representation of the object, that is unique to that object (You could actually use it to compare 2 objects and check whether they're equal or not).

As you can see, com.company.Dog@4554617c is not very readable. That's why it's recommended we override ("re-write") that original toString() method when we create a new class so we can make it return something more readable, as Craig does in the video:

@Override
public String toString() {
    return "Treet: \"" + mDescription + "\" - @" + mAuthor;
 }

So that calling treet.toString() now returns: Treet: "Want to be famous? Simply tweet about Java and use the hashtag #treet. I'll use your tweet in a new Treehouse course about data structures." - @craigdennis. We now have a more human-readable representation of that treet object.

Hope that helps :)

You're welcome Tonnie Fanadez :)

Bryan Martinez
Bryan Martinez
2,225 Points

Great explanation! Thank you for taking the time to explain it.

Thank you Bryan Martinez :) I'm glad you found it useful.

Tonnie Fanadez
Tonnie Fanadez
UX Design Techdegree Graduate 21,843 Points

Hi Carolina Estrada

Now every class in Java is a child of the Object class; Object contains toString() method which Java classes automatically inherit.

The main purpose of toString() method is to generate a String or text representation of a Java Class; in other words to provide meaningful and informative details that a person can read and understand about that Java class.

Whenever you access an Object in a String context (e.g. when using printf, println) the toString() method is invoked from under the covers to print out Object in textual format.

Consider the below code with me:

We declare a Class Girl with name, height and diet fields; we initialize these fields with values on the Girl's constructor. Inside the Girl Class, we override toString() method and set what the desired output should be when the Girl Class happens to be called in a String context.

Inside the main method we try to print out the Girl class using System.out.println()

We get this result thanks to us overriding toStringMethod() inside the Girl class

My name is carolina, I am 6 feet tall and I am a vegetarian

public class Main {


    public static void main(String[] args) {
        // creating a new instance of a Girl Class
        Girl carolina = new Girl();

        //printing out the Girl Class in text
        System.out.println(carolina);

        //Output will be "My name is carolina, I am 6  feet tall and I am a vegetarian"
    }

    //declaring a new nested class called Girl
    public static class Girl {

        private String name;
        private int height;
        private String diet;

        //initialize the above field with random values
        public Girl() {
            name = "carolina";
            height = 6;
            diet = "vegetarian";
        }

        //Override toString() to set the desired text output of our Girl class
        @Override
        public String toString() {
            return ("My name is " + name + ", I am " + height + "  feet tall " + "and I am a " + diet);

        }
    }
}
Bryan Martinez
Bryan Martinez
2,225 Points

Great explanation! Thank you