oop - java interface and child class -

this question has answer here:

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i have next question. have interface

public interface myinterface {     blah blah } 

and have child:

public class mychild implemets myinterface {     blah blah } 

what difference between:

mychild child = new mychild(); 

and

myinterface child = new mychild(); 

?

your added code snippet -

mychild child = new mychild();   

and

myinterface child = new mychild();   

in first case child can contain object of mychild class. in second case child (where child myinterface) can contain object of class implements myinterface. here can advantage of polymorphism.