instanceof ?

Im trying to use the instanceof operator within the context of error handling but the code seems to be not working properly.
I just want to specify one superclass and be able to determine which subclass is being caught. No casting is necessary since i dont need to work with the object.
Thanks for any help. :)

Code:

---

// no casting necessary
try{
.........
}catch(Exception e){
      if(e instanceof FileNotFoundException){
        FileNotFoundException fnf = (FileNotFoundException) e;
        fnf.getMessage();
      }
    }

---

Code:

---

// what i would like to do
try{
............

}catch(Exception e){
      if(e instanceof FileNotFoundException){
        System.out.println("FileNotFoundException!!!");
      }
      if(e instanceof NullPointerException){
        System.out.println("NullPointerException!!!");
    }
  }

---

Do you get any errors?
I've never used the instanceOf thingie so I'm not sure I can help you with that, but try using:
e.getClass().getSuperClass().getName()
or something like that. Not sure about the methods, but that you can look up in the API :)

Actually i figured out that another catch block was catching the Exception being thrown. So what i was trying to do might work after all. In the first if statement if the mode !null(and matches) but the file == null the compress file method is still invoked with a null string being passed to the method. I need it where if either one is null then the if statement is executed.

Code:

---

if((mode == null) || (file == null)){
    System.out.println("enter mode file");
    break; 
    }
    if(mode.equals("-c")){
        compress(file);
    }
    else if(mode.equals("-d")){
        decompress(file);
    }
    else{
    System.out.println("Correct mode needed");
    }

---

Fixed it. Changed the line to if(mode.equals("") || file.equals("")). I assumed that readLine() returned a null value when the enter key was pressed. :rolleyes:

The instanceof thing would work, but
a) getMessage is AFAIK a method of Exception too, so you can simply call it on e without any casting.
b) Have several catch blocks with diffferent classes. It's more efficient.

Yup works. :p

Code:

---

public class ThrowTest{
 public static void main(String[] args){

 try {
  int i = 7 / 0;

  }catch(Exception e){
  if(e instanceof ArithmeticException){
    System.out.println("ArithmeticException");
    System.out.println(e.getMessage()); 
    }
  if(e instanceof ClassCastException){
    System.out.println("ClassCastException");
    System.out.println(e.getMessage()); 
    }
  if(e instanceof RuntimeException){
    System.out.println("RuntimeException");
    System.out.println(e.getMessage()); 
  }
  if(e instanceof Exception){
    System.out.println("Exception");
    System.out.println(e.getMessage()); 
  }
  if(e instanceof Throwable){
    System.out.println("Throwable");
    System.out.println(e.getMessage()); 
    }
  }
 }
}

---

Code:

---

public class ThrowTest{
 public static void main(String[] args){

 try {
  int i = 7 / 0;

  }catch(Exception e){
    System.out.println(e.getClass().getName());
    System.out.println(e.getMessage());
  }
 }
}

---

or

Code:

---

public class ThrowTest{
  public static void main(String[] args){

    try {
      int i = 7 / 0;
    } catch(ArithmeticException e) {
      System.out.println("ArithmeticException");
      System.out.println(e.getMessage());
    } catch(ClassCastException e) {
      System.out.println("ClassCastException");
    } // ...
  }
}

---

The main difference to yours is that mine doesn't run the hierarchy. In your example your code would print:

Quote:

---

ArithmeticException
Integer division by zero
RuntimeException
Integer division by zero
Exception
Integer division by zero
Throwable
Integer division by zero

---

while mine would only print

Quote:

---

ArithmeticException (or java.lang.ArithmeticException)
Integer division by zero

---