java - In Object Oriented theory, should a derived class inherit a parent object's Interface? -

i'm self taught hobbyist programmer , knowledge derived seeing compiler , doesn't like.

suppose have (in c# notation, java may have other abilities)

the class need override looks this:

public interface icandosomethingelse {     void doit(); } class parent : icandosomethingelse {    public void eattacos()    {    }     void icandosomethingelse.doit(string thingtodo)    {       // implementation    } } 

so this:

class child : parent, icandosomethingelse {    new public void eattacos()    {    }    void icandosomethingelse.doit(string thingtodo) // new keyword illegal here?     {       // implementation    } } 

question

i observe new keyword illegal in interface. because explicit interface?

is there way force children implement interface, or mean need set implicit/explicit cast?

i observe new keyword illegal in interface. because explicit interface?

the error because you're implementing interface explicitly in classes.

explicit implementaton forces methods exposed when working interface directly, , not underlying implementation.

if classes this:

class parent : icandosomethingelse {    ...     public void doit(string thingtodo)    {       // implementation    } }  class child : parent, icandosomethingelse {    ...     public new void doit(string thingtodo)    {       // implementation    } } 

you need use new keyword somehow hide parent.doit implementation.

is there way force children implement interface, or mean need set implicit/explicit cast?

you can make parent class abstract, interface's methods abstract too:

abstract class parent : icandosomethingelse {    ...     public abstract void doit(string thingtodo); }  class child : parent, icandosomethingelse {    ...     public override void doit(string thingtodo)    {       // implementation    } } 

here, child must implement doit method.