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Java Java Data Structures Getting There Object Inheritance

How does Treet.java automatically calls toString() method?

Okay. For example if we want to get the author of a tweet we would call treet.getAuthor(); in the main method, but why do we don't need to call treet.toString(); in the main method? It just automatically makes it to cast it?

I understand that the toString(); method is written somewhere in the Object class.

What confuses me the most is that the objects have the same structure, but behave totally different. Sorry for my stupid question, it confuses me.

2 Answers

Thanks for your answer! Though I didn't understood it completely.


This tutorial explains this one perfectly though.

Fahad Mutair
Fahad Mutair
10,359 Points

hi Christion Gino , i found this answer on Stack Overflow

You're not explicitly calling toString(), but impliclty you are:


System.out.println(foo); // foo is a non primitive variable

System is a class, with a static field out, of type PrintStream. So you're calling the println(Object) method of a PrintStream.

It is implemented like this:

   public void println(Object x) {
       String s = String.valueOf(x);
       synchronized (this) {

As wee see, it's calling the String.valueOf(Object) method. This is implemented as follows:

   public static String valueOf(Object obj) {
       return (obj == null) ? "null" : obj.toString();

And here you see, that toString() is called.

5,604 Points

Thank you for this answer! this perfectly explains it. I was wondering the same thing after watching this video, since with every other method its necessary to call the method in order to use it. I was confused as to why the toString method is automatically implemented without calling it...

This explanation makes perfect sense though that the .toString method IS being called, but it is behind the scenes happening through a series of other methods that we don't see.

muhammad faizullah
muhammad faizullah
Courses Plus Student 8,122 Points

I'm sorry if I ask a stupid question, but what does the question mark (?) mean in the above code?

Gabbie Metheny
Gabbie Metheny
33,778 Points

Muhammad, the question mark (?) and the colon (:) are both part of the ternary operator. It's basically shorthand of writing an if/else statement: the part before the ? is the condition to test, the part after the ? but before the : is the code to run if the condition evaluates to true, and the part after the : is the code to run if the condition evaluates to false. So, in the above case, if obj is null, "null" will be returned; if it is not null, obj will be converted to a string, then returned.