How to easier print an object?

To display all the data of an object using the System.out.println(object); command in Java, there is a method called toString();.

toString()

The toString method in Java is a built-in method that belongs to the Object class. It is used to return a string representation of an object. By default, when we call toString on an object, it returns a string that contains the class name followed by the hashcode of the object. Let's look at the example:

HashCode

A hashcode, in simple terms, is a unique identifier for an object that is stored in memory. We can also see the hash code of an object by calling the hashCode() method on it, for example:

In that case, the question arises: how can we get something more specific instead of the hash code of an object? For such cases, we can override the toString() method.

Inheritance and method overriding are extensive topics that we will study in a separate course. For now, we will use method overriding only for the toString() method.

How to use toString()

To override a method, we need to use the following syntax:

Note that we use the annotation @Override before this method. With this annotation, the compiler recognizes that we are overriding this method. Next, we specify the syntax public String toString(), indicating which exact method we are overriding.

In the body of this method, we will define how our object should be represented as a string. Let's override the method for the Person class:

The System.lineSeparator() command is used to create a new line. We have defined how our object should appear by concatenating strings with their values. Therefore, when we try to print an object of the Person class, we will see detailed information about each field. Let's output an object using the main method and see how it looks:

Note

Note that we don't explicitly call the toString() method; it is automatically invoked when we pass an object to System.out.println().

We have obtained information about the class to which the object bob belongs and details about all its fields. Thus, we can override and define the toString() method to display the desired information when printing an object. Let's create another object of this class using the constructor to see and reinforce how the toString() method transforms the object:

We can see that the new object alice is displayed in the console using the same template.

Conclusion

By using the toString() method, we have greatly simplified the process of displaying object information on the screen, allowing us to save space in the main method.

Note

You can also customize the toString() method to display the desired information. Keep in mind that this method should be implemented in the class of the object you want to display on the screen.