Catching exceptions

Question

Maybe a stupid question but is there any common practice when it comes to handling exceptions in Java? Should I declare throws for the whole method or should I use a try-catch construction? I can see the advantage of passing exception to the calling methods but this means that many methods must be throwables or catch the exceptions so it's kind of a circle of exceptions...
/P

Answer 1

You usually don't want to do
catch (Exception e) {}
Somewhat less onerous is
catch (Exception e) { //handle it }
Normally what you'd do is define your own exception classes that extend Exception. A common approach is to use a package-based hierarchy, with specific exceptions for specific types of errors.
// package com.mycompany.dbstuff might have these
public class DatabaseException extends Exception { /*...*/}
public class NoSuchTableException extends DatabaseException { /*...*/ }
public class  LoginFailedException extends DatabaseException { /*...*/}
// package com.mycompany.accountmanagement package may have these
public class AccountException extends Exception {/*...*/}
public class IllegalAccountNumberExceptoin extends AccountException {/*...*/}
// etc.Each exception simply has constructors that call super(same args), and possibly the ability to take another Throwable as a constructor arg, which is then mapped to a member variable so you can later call getCause() or getWrappedException to see which exception led to this one.
At any given layer, you catch exception thrown by the layers it uses, and wrap them in an exception for your current layer.
// in the AccountClass
public AccountInfo getAccountInfo(int acctId) throws AccountException {
    if (acctId < 0) {
        throw new IllegalAccountNumberException("No negative account numbers");
    try {
        database.login(uname, passwd);
        databse.getAccountInfo(acctId);
    catch (DatabaseException exc) {
        exc.printStackTrace();
        throw new AccountException(exc);
}This way, the user of the accountmanagement package doesn't need to know what database package accountmanagement uses. If I call an accountmanagement method, I only have to deal with an account relatd exception. If it's IllegalAccountNumber, I can prompt the user to reenter the acct number. If it's other, I can say "Couldn't retrieve account info, please try again" or some such thing.
And yes, I know, if the login failed, you'd want to propagate that, so the user could reenter the password. I'd make a separate AccountLoginFailedException and wrap that around the DBLoginFailed, because the user of the Account class is trying to access the account, not the database.
Also, you often do want to print stack traces. Not in your user's face--off in a log file somehwere. If you've got exceptions that are ocurring for reasons other than user typos, you want to record as much info as you can about them.