Do interfaces have toString method? [duplicate]

Answer 1

Class C implements My but it also extends Object, as all objects eventually do in their inheritance tree.

The Object class does have the method toString(), along with a number of others.

Answer 2

The reason that you are able to invoke that method through that variable of your interfce is because of a special treatment in case of interfaces in Java.

Even though the method is not explicitly declared in the interface, the special treatment implicitly provides declarations for all the public instance methods defined in the class Object. And the toString method is one of them.

But, note that interfaces don't implicitly extend any super interface (or class) unlike classes which implicitly extend the Object class.

You will find a better explanation here - Do Interfaces really inherit the Object class in Java? .

Answer 3

You can't call for Interface toString() method because they only have the methods you declare.

But you can trick the system. Every object have a toString() method and it is obvious that your interface be implemented by class that extend object so you will have it too.

So you can do some thing like that:

public static void main(String[] args) 
    {
        My m=new C();
        String s= m + ""; // the toString() of the C class will be called here
        System.out.println(s);
    }

Answer 4

Every Object(except primitive types) in java has a toString() method.

Answer 5

Object has a toString() method, so everything (except primitive types) has a toString() method. Java will treat anything, even an empty interface, as having all the methods of Object, because it always does.

Answer 6

Any Object has a toString() method. Anything that would implement an interface will implicitly extend Object, so will also have a toString() method.