Question

I’ve created my own exception but when I try to use it I receive a message saying that it can’t be cast to my exception

I’ve got one interface like this

public interface MyInterface
{   
    public OtherClass generate(ClassTwo two, ClassThree three) throws RetryException;
}

other like this one

public class MyGenerator{   
  public class generate (ClassTwo two, ClassThree three){
    try{
    }catch(MyException my)
  }
}

and finally a method in another class

public Object evaluate(String expression, Map values) throws FirstException, RetryException
{
   try{
   }catch (Exception x){
     if(x instanceof FirstException){
       throw new FirstException()
     }
     else{
       RetryException retry= (RetryException)x;
       retry.expression = expression;
       retry.position = position;
       retry.operator = tokens[position];
       retry.operand = 1;
       throw retry; 
     }
  }
}

This try catch block on the last method is to make maths operation and I want to catch a division by zero exception on the RetryException.

Answer 1

RetryException retry= (RetryException)x; 

This line of code is attempting to cast an Exception as a RetryException. This will only work if: RetryException appropriately extends the Exception type that you are catching (ArithmeticException for divide by zero, I think?). AND the Exception actually IS a RetryException. Without looking at more of your logic, we have no idea if this is true.

Try checking

if (x instanceof RetryException)

Before you do this cast. Your code may be throwing a different kind of Exception.

Preferably, you would instead have multiple catch blocks…

try{
//}catch (FirstException e) -- I removed this, as you are only catching it and then directly
                        //     throwing it, which seems uneecessary
}catch (RetryException r){
    //process r
    throw r;
}

If I misunderstood your question, I’ll do my best to correct this.