What are the rules need to follow when overriding a method that throws an exception in Java?

We need to follow some rules when we overriding a method that throws an Exception.

• When the parent class method doesn’t throw any exceptions, the child class method can’t throw any checked exception, but it may throw any unchecked exceptions.

class Parent {
   void doSomething() {
      // ...
   }
}
class Child extends Parent {
   void doSomething() throws IllegalArgumentException {
      // ...
   }
}

• When the parent class method throws one or more checked exceptions, the child class method can throw any unchecked exception.

class Parent {
   void doSomething() throws IOException, ParseException {
      // ...
   }
   void doSomethingElse() throws IOException {
      // ...
   }
}
class Child extends Parent {
   void doSomething() throws IOException {
      // ...
   }
   void doSomethingElse() throws FileNotFoundException, EOFException {
      // ...
   }
}

• When the parent class method has a throws clause with an unchecked exception, the child class method can throw none or any number of unchecked exceptions, even though they are not related.

class Parent {
   void doSomething() throws IllegalArgumentException {
      // ...
   }
}
class Child extends Parent {
   void doSomething() throws ArithmeticException, BufferOverflowException {
      // ...
   }
}

Example

Live Demo

import java.io.*;
class SuperClassTest{
   public void test() throws IOException {
      System.out.println("SuperClassTest.test() method");
   }
}
class SubClassTest extends SuperClassTest {
   public void test() {
      System.out.println("SubClassTest.test() method");
   }
}
public class OverridingExceptionTest {
   public static void main(String[] args) {
      SuperClassTest sct = new SubClassTest();
      try {
         sct.test();
      } catch(IOException ioe) {
         ioe.printStackTrace();
      }
   }
}

Output

SubClassTest.test() method