Sensing Assertions - the case for programmatically testing whether assertions + no AssertionErrors

[Ted North]

You can programmatically test whether assertions have been enabled without throwing an AssertionError

This is from OCP Exam 3 Question 24...

Apprently, this is a true statement. I have searched the interwebs shallow and deep for something to grok, but nothing makes since.

Can some kind programmer explain this to me with:

text-based explanation

program example

psuedo-code

[Seetharaman Venkatasamy]

I do suggest you to look at Assertions

[Seetharaman Venkatasamy]

and Ted North : if you want to become a good man, you should at least taste what a bad man do. so please avoid that feeling...

[Ted North]

Seetharaman Venkatasamy wrote:I do suggest you to look at Assertions

Uh, thank-you I guess...but I am studying for 6 not 1.4

[Seetharaman Venkatasamy]

assertion introduced in 1.4 and i think there wont be a major change

[Ted North]

public class TestAssertX  {
	public static void main(String[] args) { 

	boolean assertsEnabled = false;

	assert assertsEnabled: "shock to the system... + " + " assertsEnabled = " + assertsEnabled;
	} // end main
} // end this terrible class lol 

Is this a way to test if assertions are enabled programmatically? This does throw an AssertionError though so not all the requirements are met.

programming with assertions info - scroll to the bottom to number 7...

Respectfully,

Ted North - powerhouse of industry and IT

[Ted North]

public class TestAssertX  {
	public static void main(String[] args) { 

	boolean assertsEnabled = false;

	assert assertsEnabled = true: "shock to the system... + " + " assertsEnabled = " + assertsEnabled;
	} // end main
} // end this terrible class lol 

Does changing the assertsEnabled variable to true in the assert statement fit the bill for programmatically checking if assertions are enabled without throwing any? tl:dr - does this provide an example for the initial question found in OCP Exam 3?

Respectfully,

TN - 99 percenter

[Seetharaman Venkatasamy]

Ted North wrote:

public class TestAssertX  {
	public static void main(String[] args) { 

	boolean assertsEnabled = false;

	assert assertsEnabled: "shock to the system... + " + " assertsEnabled = " + assertsEnabled;
	} // end main
} // end this terrible class lol 

Is this a way to test if assertions are enabled programmatically? This does throw an AssertionError though so not all the requirements are met.

programming with assertions info - scroll to the bottom to number 7...

Respectfully,

Ted North - powerhouse of industry and IT

if the condition failed the detailed message[ "shock to the system... + " + " assertsEnabled = " + assertsEnabled] would go to user if you metion -ed as an argument as in java -ea ClassName

if there is no such a sentence after assert boolean as in assert b; then if b is not true AssertionError will be thrown

[Ted North]

Do you think proves how the statement found in the OCP exam books is true? That was my initial question.


Thank-you for the feedback. I did run this program with the -ea flag and saw the output.

[Seetharaman Venkatasamy]

Ted North wrote:Do you think proves how the statement found in the OCP exam books is true? That was my initial question.

no idea. i just share my experience ...

[Ted North]

[Bert Bates]

I just rewrote the program and it works fine!

[Ted North]

Bert Bates wrote:I just rewrote the program and it works fine!

Hi Bert,

Thank-you for the response. This means a lot to me. My colleague was impressed you responded as well. <quick hello to work-colleague />

//Fan-boy mode off

What do you mean the program works fine?



Which one? Do you think that the program answers the question about whether, "You can programmatically test whether assertions have been enabled without throwing an AssertionError"?

Thank-you again for the reply.

Respectfully,

TN

[gurpeet singh]

maybe this will help http://www.javaworld.com/javaworld/jw-11-2001/jw-1109-assert.html?page=3. the classloader maintains mapping for the status of assertion enabled on package and classes. when it loads the class, it checks its mapping and sets a special assertion enabled flag in the class.

Maybe you can extract that "special assertion enabled flag" or the mappings programmatically.

[Henry Wong]

gurpeet singh wrote:maybe this will help http://www.javaworld.com/javaworld/jw-11-2001/jw-1109-assert.html?page=3. the classloader maintains mapping for the status of assertion enabled on package and classes. when it loads the class, it checks its mapping and sets a special assertion enabled flag in the class.

Maybe you can extract that "special assertion enabled flag" or the mappings programmatically.

I think you missed this (to be included next) post of this topic. Looks like the OP found the section in the assertion document that explains on how to test for assertions without triggering an assertion. See this ...

Ted North wrote:

public class TestAssertX  {
	public static void main(String[] args) { 

	boolean assertsEnabled = false;

	assert assertsEnabled = true: "shock to the system... + " + " assertsEnabled = " + assertsEnabled;
	} // end main
} // end this terrible class lol 

Does changing the assertsEnabled variable to true in the assert statement fit the bill for programmatically checking if assertions are enabled without throwing any? tl:dr - does this provide an example for the initial question found in OCP Exam 3?

Respectfully,

TN - 99 percenter

[Ted North]

Henry Wong wrote:

Maybe you can extract that "special assertion enabled flag" or the mappings programmatically

.

I think you missed this (to be included next) post of this topic. Looks like the OP found the section in the assertion document that explains on how to test for assertions without triggering an assertion. See this ...

Thanks Henry. I guess im not that incompetant. XD

gurpeet singh - thanks for pointing to the article in java_world about assertions. I definitely know more about class loaders now. The article pointed me toward the Java Language Specification (JLS). I downloaded the .pdf for SE6 from here: http://docs.oracle.com/javase/specs/

On pages 373-374 or pdf 407-408 there is an interesting program that has static initialization blocks and other interesting things that happen to, what I think amounts, to programatically checking to see whether assertions are enabled on the class without throwing any; which is the original question.

The code from these pages is as follows:

public class Foo { 
	public static void main(String[] args) { 
		Baz.testAsserts(); 
		// will execture after Baz is initialized.
		}
	}
	class Bar { 
		static { 
			Baz.testAsserts();
			// Will execute before Baz is initialized!
		}
	}
	class Baz extends Bar { 
		static void testAsserts() { 
			boolean enabled = false;
			assert enabled = true;
			System.out.println("Asserts " + (enabled ? "enabled" : "disabled"));
		}
	}
	

I appreciate everyone's help on this. It's an honor to have such great feedback in the java community.