Re: throwing exceptions on instantiation

From:
Knute Johnson <nospam@rabbitbrush.frazmtn.com>
Newsgroups:
comp.lang.java.help
Date:
Fri, 09 May 2008 09:15:52 -0700
Message-ID:
<482478ba$0$6948$b9f67a60@news.newsdemon.com>
thufir wrote:

On Thu, 08 May 2008 22:04:19 -0700, Knute Johnson wrote:
[...]

Just re-throw the exception.


Let's say Guest throws a DataException to FileUtils.newGuest(), which
then throws that DataException to FileUtils.loadGuest(), which means that
loadGuest() needs to try newGuest() ?

If I'm misunderstanding how it's should work, or the standard approach,
please let me know.

thufir@arrakis:~/bcit-comp2611-project1$
thufir@arrakis:~/bcit-comp2611-project1$ cat src/a00720398/util/
FileUtil.java
/**
 * FileUtil.java
 */

package a00720398.util;

import java.util.*;
import java.io.*;
import a00720398.data.*;

public abstract class FileUtil {

        public static List<String> parseGuestString (String string){

                System.out.println("\n\n\n********\n");

                List<String> guestData = new ArrayList<String>();
                Scanner lineScanner = new Scanner(string);
                while (lineScanner.hasNext()){
                        String token = lineScanner.next();
                        guestData.add(token);
                        System.out.println("\n\ntoken\t\t" + token);
                }
                return guestData;
        }

        public static Guest newGuest(String string) {
                List<String> guestData = parseGuestString(string);

// try {
                        Guest guest = new Guest(guestData);
                        return guest;
// catch (Exception e) {
// e.printStackTrace();
// }
// return new Guest();
        }

        public static List<Guest> loadGuests(File file){
                List<Guest> guests = new ArrayList<Guest>();

                try {
                        Scanner scanner = new Scanner(file);
                        while (scanner.hasNextLine()) {
                                String line = scanner.nextLine();
                                Scanner lineScanner = new Scanner(line);
                                lineScanner.useDelimiter("\n");
                                while (lineScanner.hasNextLine()) {
                                        String oneLine = lineScanner.next
();
                                        Guest guest = newGuest(oneLine);
                                }
                        }
                } catch (FileNotFoundException e) {
                        e.printStackTrace();
                }
                return guests;
        }
}
thufir@arrakis:~/bcit-comp2611-project1$
thufir@arrakis:~/bcit-comp2611-project1$ cat src/a00720398/data/Guest.java
package a00720398.data;

import java.util.*;

import a00720398.data.*;
import a00720398.util.*;

public class Guest {

        private int id = 0;

        private String
                lastName = "foo",
                firstName = "foo",
                phoneNumber = "foo",
                emailAddress = "foo@bar.com";

        private Address address;

        public Guest() {}

        public Guest(List<String> data)/* throws DataException */ {
// if (data.size() != 5){throw new DataException("expected 5
elements, got:\t\t" + data.size());}

// try {
                        id = Integer.parseInt(data.get(0).trim());
// } catch (Exception e) { //what kind of Exception is this?
// e.printStackTrace();
// throw new DataException(e.getMessage());
// }

                lastName = data.get(1);
        }

        public int getID
()
{return id;}
        //private setID(int
id) {this.id =
id;} //never change an ID

        public String getLastName
() {return
lastName;}
        public void setLastName(String
lastName) {this.lastName = lastName;}

        public String getFirstName
() {return
firstName;}
        public void setFirstName(String firstName)
{this.firstName = firstName;}

        public Address getAddress
() {return
address;}
        public void setAddress(Address address)
{this.address = address;}

        public String getPhoneNumber
() {return phoneNumber;}
        public void setPhoneNumber(String phoneNumber)
{this.phoneNumber = phoneNumber;}

        public String getEmailAddress
() {return emailAddress;}
        public void setEmailAddress(String emailAddress)
{this.emailAddress = emailAddress;}

        public String toString (){
                return
                        "\n\n\nGUEST RECORD\n" + "-----------\n" +
                        "\nid:\t\t" + getID() +
                        "\nfirst name:\t" + getFirstName() +
                        "\nlast name:\t" + getLastName() +
                        "\nemail address:\t" + getEmailAddress() +
                        address.toString();
        }
}
thufir@arrakis:~/bcit-comp2611-project1$
thufir@arrakis:~/bcit-comp2611-project1$

thanks,

Thufir


If you have say three nested method calls, one(), two() and three() and
all of them throw an exception. You can as Daniel said, only catch it
in the top level call or if you need to do some processing at the lower
level but still want to propagate the exception you can throw it again
or throw a new exception.

public void one() throws Exception {
     two();
}

public void two() throws Exception {
     try {
         one();
     } catch (Exception e) {
         // error processing here
         throw new Exception();
     }
}

public void three() throws Exception {
     throw new Exception();
}

try {
     one();
} catch (Exception e) {
}

--

Knute Johnson
email s/nospam/linux/

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