Handle and Declare rule - Ducking exceptions

[Esther Kak]

How do I fix this code to compile it successfully using Handle and Declare rule in

Exceptions

import java.io.*;
public class HandleAndDeclareException{
	public void riskyMethod() throws FileNotFoundException
	{
		System.out.println("You are in risky method");
		throw new FileNotFoundException();
	}
	public void duckingMethod() {
		System.out.println("calling risky method now");
		riskyMethod();
		System.out.println("just finished calling risky method");
	}
	public static void main(String args[])
	{
		HandleAndDeclareException a = new HandleAndDeclareException();
		a.duckingMethod();

	}
}    

[Esther Kak]

This class has two methods.
1. One riskyMethod() that throws and exception
2. One duckingMethod() that calls the riskyMethod.

And now, in the main() method...I am calling the duckingMethod. I know we have to Handle and declare rule - how do I implement this rule in the above code

[avi sinha]

  import java.io.*;
public class HandleAndDeclareException{
	public void riskyMethod() throws FileNotFoundException
	{
		System.out.println("You are in risky method");
		
			throw new FileNotFoundException();
		
	}
	public void duckingMethod() {
		System.out.println("calling risky method now");
		
             // handling the risky part
		try{
		riskyMethod();
		}catch(FileNotFoundException fe){
			System.out.println("caught a FileNotFoundException");
		}
		
		System.out.println("just finished calling risky method");
	}
	public static void main(String args[])
	{
		HandleAndDeclareException a = new HandleAndDeclareException();
		a.duckingMethod();

	}
}      

avi sinha

[avi sinha]

even a better idea : not just to get the code compiled

 
import java.io.*;
public class HandleAndDeclareException{
	public void riskyMethod() throws FileNotFoundException
	{
		System.out.println("You are in risky method");
		
			throw new FileNotFoundException();
		
	}
	public void duckingMethod() {
		System.out.println("calling risky method now");
		
		try{
		riskyMethod();
		}catch(FileNotFoundException fe){
			System.out.println("caught a FileNotFoundException\n");
			fe.printStackTrace();
		}
		
		System.out.println("just finished calling risky method");
	}
	public static void main(String args[])
	{
		HandleAndDeclareException a = new HandleAndDeclareException();
		a.duckingMethod();

	}
}    
   

avi sinha

[Esther Kak]

Thanks...now I understood the rule Handle & Declare
But in K&B exam watch (page 362) it says

When an object of a subtype of Exception is thrown, it must be handled
or declared.

So...does that mean it can be either handled or declared. How can I apply to my example below.

As said in K&B if I have a userdefined Exception class like this:

  public class UserDefinedException extends Exception{ }  

Suppose, I am throwing the userdefined Exception in the risky method - How do I handle? How do I declare.

 public class UserException {
	public void riskyMethod() throws UserDefinedException{      //declared exception here
		throw new UserDefinedException();      //threw exception

	}
	public static void main(String args[]){
		UserException u = new UserException();
		u.riskyMethod();
	}

}   

[avi sinha]

you have got two options here

1st one : handle the risky method invocation

  
try{
u.riskyMethod(); 
}catch(UserDefinedException e(){
// show stack trace
}
  

2nd one eclare that the method (main here) which contains the risky method invocation throws the Exception

  
 public static void main(String args[]) throws UserDefinedException{  
        UserException u = new UserException();  
        u.riskyMethod();  
    }  
  

for every checked exception either you will have to declare it or handle it (to get compiled successfully)
and all user created exceptions are checked exceptions

avi sinha