Re: typesafe java.util.Map construction and initialization

From:

Lew <conrad@comcast.net>

Newsgroups:

comp.lang.java.help

Date:

Wed, 20 Sep 2006 22:31:43 -0400

Message-ID:

<xb-dnWf0R-sNZIzYnZ2dnUVZ_rqdnZ2d@comcast.com>

Josef Svitak <jsvitak@gmail.com> writes:

// Can I do this... (doesn't work)
theMap = new java.util.HashMap( keys, bars );

Tor Iver Wilhelmsen wrote:

No, there is no auto-fill constructor. Use

theMap = new java.util.HashMap<String,BarIF>();
assert(keys.length == bars.length);
for (int i = 0; i < keys.length; i++) {
theMap.put(keys[i], bars[i]);
}

The assert is only useful if the keys and bars arrays are under the control of
the class, not parameters passed from the outside. Asserts enforce provable
conditions in an algorithm, and are not suitable for, e.g., argument checking.

In other words, the assert makes sense if it enforces that your own code has
already guaranteed that the lengths are equal.

As part of a short newsgroup example, the assert lets you know that you should
have guaranteed the condition - i.e., the poster is warning you to make sure
the assert holds, not suggesting that you use assert to check that the lengths
are equal.

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

- Lew