Assertion facility is added in J2SE 1.4. In order to support this facility J2SE 1.4 added the keyword assert to the language, and AssertionError class. An assertion checks a boolean-typed expression that must be true during program runtime execution. The assertion facility can be enabled or disable at runtime.
Declaring Assertion
Assertion statements have two forms as given below
assert expression;
assert expression1 : expression2;
The first form is simple form of assertion, while second form takes another expression. In both of the form boolean expression represents condition that must be evaluate to true runtime.
If the condition evaluates to false and assertions are enabled, AssertionError will be thrown at runtime.
Some examples that use simple assertion form are as follows.
assert value > 5 ;
assert accontBalance > 0;
assert isStatusEnabled();
The expression that has to be asserted runtime must be boolean value. In third example isStatusEnabled() must return boolean value. If condition evaluates to true, execution continues normally, otherwise the AssertionError is thrown.
Following program uses simple form of assertion
//AssertionDemo.java
Class AssertionDemo{
Public static void main(String args[]){
System.out.println( withdrawMoney(1000,500) );
System.out.println( withdrawMoney(1000,2000) );
}
public double withdrawMoney(double balance , double amount){
assert balance >= amount;
return balance ? amount;
}
}
In above given example, main method calls withdrawMoney method with balance and amount as arguments. The withdrawMoney method has a assert statement that checks whether the balance is grater than or equal to amount to be withdrawn. In first call the method will execute without any exception, but in second call it AssertionError is thrown if the assertion is enabled at runtime.
Enable/Disable Assertions
By default assertion are not enabled, but compiler complains if assert is used as an identifier or label. The following command will compile AssertionDemo with assertion enabled.
javac ?source 1.4 AssertionDemo.java
The resulting AssertionDemo class file will contain assertion code.
By default assertion are disabled in Java runtime environment. The argument ?eanbleassertion or ?ea will enables assertion, while ?disableassertion or ?da will disable assertions at runtime.
The following command will run AssertionDemo with assertion enabled.
Java ?ea AssertionDemo
or
Java ?enableassertion AssertionDemo
Second form of Assertion
The second form of assertion takes another expression as an argument.
The syntax is,
assert expression1 : expression2;
where expression1 is the condition and must evaluate to true at runtime.
This statement is equivalent to
assert expression1 : throw new AssertionError(expression2);
Note: AssertionError is unchecked exception, because it is inherited from Error class.
Here, expression2 must evaluate to some value.
By default AssertionError doesn't provide useful message so this form can be helpful to display some informative message to the user.
Rahim Vindhani
Application Develper [Application Development & Webservices]
IBM Global Services, pune, India
email: rahim.vindhani@gmail.com
web: http://www.rahim.co.nr
The objective for Zandi Digital is to make available clever... Read More
It is really interesting that a bug can create problem... Read More
What is Spyware?Spyware monitors your surfing habits and sends the... Read More
The purpose of one of our projects was MS Exchange... Read More
Microsoft Great Plains serves the wide spectrum of horizontal markets.... Read More
MSN messenger is a pretty cool invention. I mean I'm... Read More
Since technology changes so quickly, it is hard to begin... Read More
The Microsoft system preparation utility for Windows 2000 is a... Read More
Running Applications in Compatibility Mode With Windows XP, you can... Read More
In the Clinton era the status quo was simple: you... Read More
The Windows Indexing Service provides you with the ability to... Read More
Using professional icons in your application or website can bring... Read More
Learning how to program software seems like a daunting task... Read More
When it comes to screenplay software each screenwriter needs to... Read More
Shareware has been fighting the stigma of being misunderstood for... Read More
1. What determines the software price? Is it Per Seat... Read More
Is your PC is slow and wimpy? Then you need... Read More
Looks like Microsoft Great Plains becomes more and more popular,... Read More
As we could imagine, if you are reading this article... Read More
Microsoft Business Solutions Great Plains was historically designed to serve... Read More
I have always had a tendency to focus on the... Read More
Microsoft Business Solutions Great Plains is very good fit for... Read More
Professional services firm cuts costs and improves productivity with integrated... Read More
While paper labeling CDs and DVDs may appear to be... Read More
FTP stands for "file transfer protocol". FTP is basically a... Read More
licensed cleaning services Lake Forest ..While several preventive maintenance software manufacturers offer free trials for... Read More
Looks like Microsoft Great Plains becomes more and more popular,... Read More
This article is the third of a series of articles... Read More
Looks like Microsoft Great Plains becomes more and more popular,... Read More
Lotus Notes Domino is very efficient in electronic document workflow... Read More
It???s easy to understand why you might be drawn to... Read More
Microsoft Business Solutions Great Plains serves to the wide spectrum... Read More
Designing without tables by using CSS layouts is fast becoming... Read More
Java has come along a long way. Many would agree... Read More
If you are software developer or database administrator - we... Read More
Looks like Microsoft Great Plains becomes more and more popular,... Read More
Program Flow is what you think it is. How the... Read More
Imagine something that follows you home and sets itself up... Read More
Microsoft Great Plains could be tuned and setup to fit... Read More
GroupwareThe internet is full of 1.5 million to 7 million... Read More
We were recently faced with a decision: either to let... Read More
All of us know that Microsoft bought former Great Plains... Read More
A LOT OF UNWANTED FILES.When you uninstall an item of... Read More
Considering whether or not your software company should hire a... Read More
Trying to figure out a stream in banning one email... Read More
Our opinion is based on our Microsoft Business Solutions Great... Read More
If you have Microsoft Great Plains and support it for... Read More
Executive SummaryAn effective plan for entering, cleaning and updating the... Read More
We would like to give you several situations, when you... Read More
Assertion facility is added in J2SE 1.4. In order to... Read More
Software |