Do Java Interfaces Inherit from the Object Class?

Do Interfaces Inherit from Object Class in Java?

In Java, interfaces act as blueprints for declaring method signatures and providing abstract implementations. One common misconception is whether interfaces inherit from the Object class like standard classes do.

No Inheritance from Object Class

Contrary to popular belief, interfaces do not inherit directly from the Object class. This means they do not have access to methods like equals(), hashCode(), toString(), or wait() by default.

Calling Object Class Methods on Interfaces

Despite not inheriting from Object, interfaces can still call methods from the Object class. This is because interfaces implicitly declare public abstract methods corresponding to all the public instance methods in Object, unless they already inherit these methods from a superinterface.

For example, consider the following code:

<code class="java">interface Employee {
}

public class Test {
    public static void main(String[] args) {
        Employee e = null;
        e.equals(null);
    }
}</code>

In this code, the Employee interface doesn't explicitly declare an equals() method. However, the expression e.equals(null) compiles successfully because the equals() method is implicitly declared in Employee (and all other interfaces) as a public abstract method.

Reason for Implicit Interface Declaration of Object Methods

This implicit declaration of Object methods in interfaces allows interfaces to interact seamlessly with the broader Java ecosystem. It enables interfaces to take advantage of standard library methods for object comparison, hashing, string representation, and synchronization without explicitly defining these methods.

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