[jsword-devel] java assertions

[DM Smith]

The other thing about assertions that require caution is that they can be 
removed at the command line.

So the example you give where the action is only to happen based on the 
outcome of the test should never become:
assert condition;
doit();

and be as you have it.

It seems that asserts should only be used to test conditions that are 
expected to always or never to happen. I.e. a double check against "Stupid 
Programmer Errors."

An assert should never be used as a control construct.

If we have used LogicError only for conditions that cannot happen they I 
think they can be replaced with an assert.

The use of an assert should be a self documenting statement that that code 
should never be reached.

So I vote that LogicError be replaced (carefully) with asserts and for those 
places where it should not have been used, a LucidException, which is 
unchecked.




Joe Walker writes:
>
>The interesting thing about assertions that is different from LogicError is 
>that in normal use they don't unwind the stack. So there are times when we 
>should alter things a bit.
>The example I'm just looking at in common/...util.Convert.java had 
>something like the following:
>
>if (<TEST>)
>{
>     throw new LogicError();
>}
>
><ACTION>
>
>It might be tempting to change this to:
>
>assert <TEST>;
><ACTION>
>
>However the idea behind assert is that in devel test we get to know ASAP 
>when something is not right, but if it goes wong in live then things might 
>just be able to limp along. The code above will not limp on well if 
><ACTION> depends on <TEST> being false.
>So we can do this:
>
>if (<TEST>)
>{
>     assert false;
>}
>else
>{
>     <ACTION>
>}
>
>Joe.
>
>DM Smith wrote:
>>I was curious about java's assertions since I have not used them.
>>http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html gives a 
>>tutorial.
>>According to 
>>http://leepoint.net/notes-java/20language/30statements/40assertions/20assert-usage.html 
>>:
>>    You need to compile with the -source 1.4 flag to prevent assertions 
>>from being compiled out.
>>    You need to run the program with -ea or -enabledassertions as an 
>>argument to the vm.
>>
>>Because assertions may be compiled out, the test must be free of side 
>>effects.
>>
>>When the argument to an assert is false, it throws an AssertionError.
>>A second argument can be supplied to an assertion to provide greater 
>>detail that analysis of the code could not.
>>
>>This can easily replace many uses of LogicError, but not when the purpose 
>>is to rethrow caught Exception.
>>
>>if (a == b)
>>{
>>    throw new LogicError("Oops");
>>}
>>
>>can become:
>>assert a!=b;
>>
>>However:
>>try
>>{
>>    doit();
>>}
>>catch (Throwable t)
>>{
>>    throw new LogicError(t);
>>}
>>
>>would become:
>>try
>>{
>>    doit();
>>}
>>catch (Throwable t)
>>{
>>    assert false : t.getMessage();
>>}
>>
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