Understanding assertion mechanism

[Mckenzie John]

Hi ,

I have a doubt regarding the assertion mechanism. Let me explain:

// code
assert( value >= 0 && value <= 20 ) : "Invalid number: " + value;
// coding continues

In the above scenario,

1) when is the assertionError thrown? when the condition is false - Is the value is printed as similar to an SOP along with the stackTrace?

2) If the condition is true , say the relational operator returns true , the coding continues without printing the value . Is my understanding correct?

3) In SCJP real exam, what answer must i choose if i get a question like the above is asked - what is the output of an assert statement - without mentioning anything about it being enabled or disabled? I know that assertions are disabled by default. So should i assume that even though assertion is present it has no use as assertion is not enabled and mark the choice that the coding proceeds normally?


Thanks in Advance.

Regards,
Mck

[nir sharma]

your first and second statements are correct. And you can run your program to see the exact stacktrace.
In regard to the third statement I think you should consider that the assertion is enabled however I would like other ranchers to back my statement.

[Seetharaman Venkatasamy]

Mckenzie John wrote:
1) when is the assertionError thrown? when the condition is false - Is the value is printed as similar to an SOP along with the stackTrace?

assert( value >= 0 && value <= 20 ) : "Invalid number: " + value; 

the above one is interpreted by compiler as in

if( value < 0 || value > 20 ) {
   throw new AssertionError((new StringBuilder("Invalid number: ")).append(value).toString());
}

So, that means you are passing the error message to AssertionError's constructor . you can get the message using getMessage() in future.

2) If the condition is true , say the relational operator returns true ,
the coding continues without printing the value . Is my understanding correct?

Yes, with out throwing an Error.

3) In SCJP real exam, what answer must i choose if i get a question like the above is asked - what is the output of an assert statement - without mentioning anything about it being enabled or disabled? I know that assertions are disabled by default. So should i assume that even though assertion is present it has no use as assertion is not enabled and mark the choice that the coding proceeds normally?

Here I am not sure. hope, some other rancher can help you