Exception handling in method overriding in java

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Java

exceptions

In exception handling, it is known that, if the superclass method does not declare an exception, subclass overridden method cannot declare the checked exception but it can declare unchecked exception. Why so? consider the following example :

import java.io.*;  
class Parent{  
  void msg(){System.out.println("parent");}  
}  
  
class TestExceptionChild extends Parent{  
  void msg()throws IOException{  
    System.out.println("TestExceptionChild");  
  }  
  public static void main(String args[]){  
   Parent p=new TestExceptionChild();  
   p.msg();  
  }  
}

What I have tried:

We get compilation error here. If I need to read a file in the overridden method "msg", then I have to mention "throws IOException" there. But java doesn't allow them. Can anyone explain this?