Do interfaces have toString method? [duplicate]

Answer 1

The the Java Documentation says...

When an interface has no direct SuperInterface, it will create abstract public method for all those public methods present in the Object class.

This is why you are able to call the toString() method on the interface reference

Answer 2

Since class Demo implicitly extends class Object, it inherits method toString. And since that's not an abstract method, class Demo is not forced to provide an implementation, although you're able to directly invoke toString on an instance of Demo. For more information, please see Lesson: Interfaces and Inheritance.

As stated in the Object API,

Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.

Also, note that the toString method is not part of the interface definition, but rather the Object class definition.