While trying to understand the concept of exception in java , it becomes necessary to understand the hierarchy of exceptions becauce
we can see a famous interview question from exception hierarchy in java developer interview.
suppose we have a parent class with a method that throws IO exception , also there is a sub class that overrides the method of parent class throws FileNotFoundException , will this code works fine or not?
The answer is no because in Java the overridden method in the subclass cannot throw a broader or more general exception than the method in the parent class.
In our scenario IOException is a broader exception than FileNotFoundException, so the overriding method in the subclass is not allowed to throw FileNotFoundException (which is a subclass of IOException) .
let us understand by an example :
We have a parent class
import java.io.FileNotFoundException;
import java.io.IOException;
class ParentClass {
// Method that throws a narrower exception
public void Method() throws FileNotFoundException {
System.out.println("IncorrectParentClass: Method");
if (true) {
throw new FileNotFoundException("FileNotFoundException from ParentClass");
}
}
}
Now we are inheriting all the features of super class in our base
class:
class ChildClass extends ParentClass {
// Overriding method that throws a broader exception
@Override
public void Method() throws IOException {
System.out.println("IncorrectChildClass: Method");
if (true) {
throw new IOException("IOException from ChildClass");
}
}
}
Now Declaring Main class:
public class Main {
public static void main(String[] args) {
ParentClass parent = new ParentClass();
ChildClass child = new ChildClass();
try {
parent.Method();
} catch (FileNotFoundException e) {
System.out.println("Caught FileNotFoundException from parent: " + e.getMessage());
}
try {
child.Method();
} catch (IOException e) {
System.out.println("Caught IOException from child: " + e.getMessage());
}
}
}
When we try to compile Main.java along with ParentClass.java and ChildClass.java, you will get a compilation error indicating that IOException is broader than FileNotFoundException.
The ChildClass will not compile because it violates the rule that an overriding method cannot throw a broader exception than the method it overrides.
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