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How can I override object methods inside interface?

All classes in java extend the Object class implicitly. But that doesn’t concern interfaces. Interfaces can only extend other interfaces, but no classes. However, I can override object class methods inside my interface.

public interface NewInterface {
    @Override
    boolean equals(Object var1);

    @Override
    int hashCode();
}

Can you please explain in simple words how is this even possible? Is there any use case for this?

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Answer

Interface is a just contract. It says that all classes that inherits interface should implement these methods. Interface cannot have implementation. It is possible to override a class that implements this interface.

However, from Java 8 you can define static methods in interfaces in addition to default methods.

UPDATE:

The members of an interface are:

  • Those members declared in the interface.
  • Those members inherited from direct superinterfaces.
  • If an interface has no direct superinterfaces, then the interface implicitly declares a public abstract member method corresponding to each public instance method declared in Object, . It is a compile-time error if the interface explicitly declares such a method m in the case where m is declared to be final in Object. Now it is clear that all superinterface have abstract member method corresponding to each public instance method declared in Object .

Read more about interface members here

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