Assertion question

[Dan Xu]

 
class A
{
  void m1(int i) {
    int j = i % 3;
    switch (j)
    {
      case 0: System.out.print("0"); break;
      case 1: System.out.print("1"); break;
      default:
        assert j == 2;
        System.out.print(j);
    }
 
}
  public static void main (String[] args)
  {
    A a = new A();
    for (int i=5; i >= -1; i--) {a.m1(i);}
  }
 
}
 

Ans:With assertions enabled it prints 210210 followed
by an AssertionError message.
With assertions disabled it prints 210210-1


--really need someone to explain it to me.can't understand.
and if i want to complie,what's command i need to input

How to fix the following error to make the program work?
Asser.java:10: warning: as of release 1.4, assert is a keyword, and may not be used as an identifier
assert j == 2;
^
Asser.java:10: ';' expected
assert j == 2;

Thanks a lot.

[Vasanth Raja.K.]

Hi Dan,
If u want to use assertion u have to put
javac -source 1.4 <Source File Name>.

For Execution
java -ea <Class Name>
or
java -enableassertions <Class Name>

Syntax for Assertion is:
assert <boolean expression>:expression
If the boolean expression is false and the assertions enabled,expression value is passed to Assertion Error Constructor.This value is converted into string format when assertion fails.

Hope u understood.
Reg
Vasanth

[Philip Heller]

More on assertions and when to use them in Chapter 5 of "Complete Java 2 Certification".

-- Phil

[Dan Xu]

I only have this one
JAVA 2 sun certified programmer & developer

[Barry Gaunt]

Programming with Assertions (part of SDK documentation)

[Kanchan K Bulbule]

210210 get printed for the values of i from 5 to 0 .

When i=-1 , it goes into the default case of the switch statement.
and it fails at the assertion ie assert i==2 and hence it gives the assertionError (when assertion are enabled ) and thus terminates .

when we disable assertion the assert command is not executed and system print the -1 value of the i.


For more detailed information. Kindly refer to the sample chapter by Khalid Mohamad on assertion at
http://www.ii.uib.no/~khalid/pgjc/jcbook/new-exam-note-020928.html

Hope this answers your queries.

Cheers
Kanchan
Preparing for SCJP 1.4

[Smitha Ballikar]

Hi Dan,

If you had queries in compiling and running this program then I think it is answered by Vasanth.

However regarding the logic,lets go through it step by step

When i=5,j=5%3=2
In switch construct, default is executed since none of the case labels match.Here since assertion is enabled assert condition is checked which is true(j==2) and 2 is printed.

when i=4,j=4%3=1
In switch construct , the matching case is executed i.e case 1 and 1 is printed.


when i=3,j=3%3=0
In switch construct , the matching case is executed i.e case 0 and 0 is printed.



when i=2,j=2%3=2
In switch construct, default is executed since none of the case labels match.Here since assertion is enabled assert condition is checked which is true(j==2) and 2 is printed.

when i=1,j=1%3=1
In switch construct , the matching case is executed i.e case 1 and 1 is printed.

when i=0,j=0%3=0
In switch construct , the matching case is executed i.e case 0 and 0 is printed.

when i=-1 j=-1%3=-1
default is executed since j==2assertion fails and assertion error is thrown

Similarly if assertion is disabled the same thing happens only -1 is printed and assertion error is not thrown

So output is 210210 Assertion Error(In assertion enabled)
and 210210 -1 (if assertion disabled)

Hope you got it!!

Cheers
Smitha