Interfaces and Object Class: Inheritance and Method Invocation

In Java, interfaces offer a means of defining contracts that classes can implement. When considering the relationship between interfaces and the Object class, it raises the question of inheritance.

Do Interfaces Inherit from Object Class?

The answer is no. Interfaces do not inherit from the Object class. Unlike classes, there is no implicit inheritance of any common root interface by all interfaces.

Method Invocation on Interface Instances

Despite not inheriting from Object, you can invoke methods like equals() on interface instances. How is this possible?

Each interface implicitly declares a public abstract method for every public method in Object. Therefore, even if an interface does not explicitly declare the equals() method, it is implicitly declared as a member.

Java Language Specification Details

The Java Language Specification (JLS) provides details on this behavior in § 9.2 Interface Members:

• If an interface has no direct superinterfaces, it implicitly declares a public abstract member method for each public instance method in Object.
• This applies unless a method with the same signature, return type, and a compatible throws clause is explicitly declared by the interface.

Conclusion

Interfaces in Java do not inherit from Object. However, they implicitly declare methods for all public Object methods to ensure compatibility and allow method invocation on interface instances.