Re: Checking for null parameter

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 11 Jun 2008 08:38:31 -0700 (PDT)

Message-ID:

<eb38c2e6-26fc-4952-b4e0-cdc1821545c9@27g2000hsf.googlegroups.com>

pek wrote:

Oh, and by the way, did anybody read this:

"Do not use assertions for argument checking in public methods..... "

fromhttp://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html

Uhm, so I guess

    public void connect() throws ConnectionException {
      assert conn != null;

      try {
        conn.connect();
      } catch (ConnectionExcetpion e) {
        // Delegate the exception
        throw new ConnectionException("Connection failed in Chat=

",e);

}
}

this would violate what you just read because a NullPointerException
isn't thrown.

It does not violate what you just read, because 'conn' is not a
parameter to the public method. In this context, 'assert' was not
used for argument checking. Notice that the method, by your own
definition BTW, takes no arguments.

Look carefully. The 'assert' declares an algorithmic invariant that
should be enforced in the constructor. The AssertionError is the
programmer's clue that they didn't do that correctly.

Again, note that this is not an example of using 'assert' for argument
checking, given that the method takes no arguments.

--
Lew