Introduction to
Assertions
has introduced in 1.4 versions. The main objective of assertions is to perform debugging.
The traditional way of debugging is to use System.out.println’s. But the main
disadvantage of this approach is compulsory we should remove these S.O.P’s
after fixing the problem other wise these will execute at run time. Which may
effect performance of the system. It may reduce readability of the code and
disturbs logging mechanism. To resolve all these problems sun people has introduces
Assertions concept in 1.4 version.The
main advantage of assertions is we can enable or disable assertions based on
our requirement. But by default assertions are disabled. Assertions concept we
have to use in Test environment or in Development environment but not in the
production.
Identifier Vs Keyword
Assert keyword has introduced
in 1.4 version hence from 1.4 version on words we are not allowed to use assert
as identifier.
Ex:-
class Test
{
public static void main(String[] args)
{
int assert = 10;
System.out.println("assert");
}
}
in 1.4 or 1.5 if we compile
javac assert.java then we
will get the following C.E as of release 1.4 assert is a keyword and may not
used as an identifier.
javac –source 1.3 assert.java
java Test
Types of assert statement. There
are 2 types of assert statement
1) simple assert.
2) Augmented assert.
Simple assert
Syntax: assert <boolean expression> ;
assert(b);
If b is true then normal
continuation follows. Else the program will terminate abnormally can rise assertion
error.
Ex:-
class Test
{
public static void main(String[] args)
{
int x = 10;
:
:
assert(x>10)
System.out.println(x);
}
}
1) javac Test.java
2) java Test
in this case assert statement
won’t be executed because it is disable by default.
3) java –ea Test
Then generates assertion error.
Augmented Version
Syntax: assert <boolean expression> : <message
expression> ;
Assert e1:e2;
‘e1’ à should be boolean type.
‘e2’ àany thing is allowed including method calls also
Ex:-
class Test
{
public static void main(String[] args)
{
int
x = 10;
;
;
assert(x>10):"here the value of x
should be > 10 but it is "+x;
System.out.println(x);
}
}
javac Test.java
java –ea Test
O/P:-
D:\javawork>java –ea Test
Exception in thread “main”
java.lang.AssertionError: here the value of x should be >10 but it is 10 at
Test.main(assert.java:8)
Note: assert e1:e2
Here ‘e2’ will be executed iff ‘e1’
is false.
Ex:-
class Test
{
public static void main(String[] args)
{
int x = 10;
;
;
assert(x==0):++x;
System.out.println(x);
}
}
javac Test.java
java –ea Test
O/P:-
D:\javawork>java –ea Test
Exception in thread “main”
java.lang.assertionError:11 at Test.main(assert.java:8)
Note:
assert(e1):e2;
for e2 any thing is allowed
including method calls also But void return type method calls are not allowed.
Violation leads to compile time error.
Ex:-
class Test
{
public
static void main(String[] args)
{
int x = 10;
;
;
assert(x>0):m1();
System.out.println(x);
}
public
static void m1()
{
return;
}
}
javac Test.java
java –ea Test
O/P:-
D:\javawork>javac
assert.java
Assert.java:8: ‘void’ type
not allowed here assert(x>0):m1();
Various Run Time Flags
1) -ea :- To enable assertions in every non-system class(i.e
user defined
class)
2) -enableassertions :- To enable assertions in every non-system class(Exactly
similar to -ea)
3) -da :- To disable assertions in every non-system class.
4) -isableassertions :- To disable assertions in every non-system class.(Exactly
similar to -da)
5) -esa :- To enable assertions in every system class
6) -enablesystemassertion :- similar to -esa
7) –dsa :- To disable assertions in every system class.
8)
-disablesystemassertions :- similar to ‘-dsa’
Ex:- java –ea –esa –da –dsa –ea Test
All the flags will execute
from left to right and there is no priority difference b/w enabling and
disabling
à To enable assertions only in the ‘A- Class’
java -ea:Pack1.A
à To enable assertions only in B and D
java -ea:Pack1.B
-ea:Pack1.Pack2.D
à To enable assertion in all classes of Pack1 and its
sub package classes also.
java –ea:Pack1…
à To enable assertions in all classes present in pack1
but not those present in pack2
java -ea:Pack1…
-da:Pack1.Pack2…
Note:- we can enable
assertions either class wise or package wise also.
Proper and Improper Use of
assertions
1)
It is improper to
use assert statement for validating the arguments of a public method.
public void withdraw(double
amount)
{
assert(amount
>= 100);
}
C.E:- No C.E, R.E it is improper
use.
2) It is improper to use
assertions for validating command line argument also, because these are
arguments to public main method.
3) It is proper to use
assertions for validating private method argument.
4) It is improper to mix
programming language with assert statement.
5) In our code if there is
any place where the control is not allowed to reach. It is the best place to
use the assert statement.
Pack1
A.class
B.class
C.class
D.class
Pack2
Ex:- switch (month)
{
case 1:
....
....
case 2:
....
....
case 3:
....
....
case 4:
....
....
:
:
:
case 12:
....
....
default:
assert(false);
}
AssertionError
It is the child class of
Error and it is unchecked. It is not recommended to catch AssertionError by
using catch Block. It is stupid type of activity.
Ex:-
class Test
{
public
static void main(String arg[])
{
int x = 10;
;
;
;
try
{
assert(x>10);
}
catch (AssertionError e)
{
System.out.println("I am stupid...Because I am
catching
Assertion");
}
}
}
O/P:-
D:\javawork>java –ea Test
I am stupid… Because I am
catching Assertion
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