Does an interface by default extend Object?

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Then from where the equals method come, is the interface also extends the super class Object ?, if that true how an interface can extends a class?

The Java Language Specification deals with this explicitly.

From section 9.2:

If an interface has no direct superinterfaces, then the interface implicitly declares a public abstract member method m with signature s, return type r, and throws clause t corresponding to each public instance method m with signature s, return type r, and throws clause t declared in Object, unless a method with the same signature, same return type, and a compatible throws clause is explicitly declared by the interface.

Basically, this is so that you can use equals, hashCode etc - because the way that the Java language is specified means that any concrete implementation of the interface will be a class, and that class must ultimately be a subclass of Object, so the members will definitely be present.

To put it another way, while the interface itself doesn't extend Object, it is known that any implementation will.

Here the class A no need to implements the method toString() as it's present in Object class. Then what is the objective of defining those method in collection interface as they can't force there implementation class to implement those method.

Usually this is just done for clarity, e.g. to document what is expected of an implementation in terms of the members declared in Object.

Does An Interface Extend Object Class In Java.?, Along with abstract methods, an interface may also contain constants, default methods, static methods, and nested types. Method But a class describes the attributes and behaviors of an object. An interface can extend multiple interfaces. Whether an instance implements an interface or not is completely irrelevant to this point. Object is a class, and interfaces can not extend classes, so "no" - the interface doesn't inherit anything from any class.

Every class implicitly extends Object and so inherits every (non-private) method of the Object class.

Every instance has a class and therefore has all of the method of Object.

Whether an instance implements an interface or not is completely irrelevant to this point.

Object is a class, and interfaces can not extend classes, so "no" - the interface doesn't inherit anything from any class.

Java - Interfaces, An interface cannot extend a class but it can extend another interface in the same Along with abstract methods, an interface may also contain constants, default An interface definition defines the 'shape' of an object by making a contract� As said an Interface does not extend Object, but any object instance of a certain interface will extend Object (because all actual classes extend Object). So that's why you can do (where MyInterface is an empty interface): MyInterface interfaceInstance = new MyInterface() { }; Object object = interfaceInstance;

A Java Interface does not extend the java.lang.Object class but instances of objects that implement the interface extend the Object class otherwise if Java Interfaces allowed to extend the java.lang.Object class then Java would support multiple inheritance of which it does not in its language specification.

Consider the scenario below:

interface MyInterface
{ 
   // interface methods here
}
MyClass extend java.lang.Object implements MyInterface
{ 
   // override methods or interface method implementations
}

Now if MyInterface extends java.lang.Object class then that would mean the MyClass would also be extending the MyInterface interface by construction creating multiple inheritance. So makes sense that Java interfaces do not extend the java.lang.Object class as this would create chaos due to multiple inheritance.

Can an interface extend a class just like a class implements , An interface in the Java programming language is an abstract type that is used to specify a All methods of an Interface do not contain implementation (method bodies) as Object (the root class of the Java type system); multiple inheritance of classes is not allowed. Example: public interface Interface1 extends Interface2;. The answer for this can be that if interfaces dont inherit methods from Object, then there would not be a default way to validate if two interface objects are equal, and also the interfaces would not get that Object's behavior that all classes get by default.They don't extend object.

Interface (Java), An interface can extend other interfaces, just as a class subclass or extend The interface body can contain abstract methods, default methods, and static� Interfaces in java don’t inherit from Object class. They don’t have default parent like classes in java. But, following two cases may surprise you. Case 1 : If an interface does not extend Object class, then why we can call methods of Object class on interface variable like below ?

Defining an Interface (The Java™ Tutorials > Learning the Java , An interface contains variables and methods like a class but the methods in an interface are abstract by default unlike a class. An interface extends another interface like a class implements an interface in interface inheritance. A program that demonstrates extending interfaces in Java is given as follows: Example. Live Demo

Extending Interfaces That Contain Default Methods. When you extend an interface that contains a default method, you can do the following: Not mention the default method at all, which lets your extended interface inherit the default method. Redeclare the default method, which makes it abstract. Redefine the default method, which overrides it.

Comments

Thank you very much So we can say that interfcae do not extend the object class, What is the answer of my second questions about Set interface why they have define those method.
@KrushnaCh.Dash: See the end of my answer. The documentation for Set.hashCode and Set.equals provide more details about the expected behaviour.
Well, OP is talking about interfaces.
@RohitJain better now? I thought what I was dayin