Question 1

Which of the following statements is true?

Accepted Answer

Adding an assertion statement to a switch statement that previously had no default case is considered an excellent use of the assert mechanism. Option A is incorrect because only Java expressions that return a value can be used. For instance, a method that returns void is illegal. Option C is incorrect because the expression after the colon must have a value. Option D is incorrect because assertions throw errors and not exceptions, and assertion errors do cause program termination and should not be handled.

Question 2

Which of the following statements is true?

Accepted Answer

Option C is true because multiple VM flags can be used on a single invocation of a Java program. Option A is incorrect because at runtime assertions are ignored by default. Option B is incorrect because as of Java 1.4 you must add the argument -source 1.4 to the command line if you want the compiler to compile assertion statements. Option D is incorrect because the VM evaluates all assertion flags left to right.

Question 3

Which three statements are true? Assertion checking is typically enabled when a program is deployed. It is never appropriate to write code to handle failure of an assert statement. Assertion checking is typically enabled during program development a…

Accepted Answer

(1) is wrong. It's just not true. (2) is correct. You're never supposed to handle an assertion failure. (3) is correct. Assertions let you test your assumptions during development, but the assertion code—in effect—evaporates when the program is deployed, leaving behind no overhead or debugging code to track down and remove. (4) is wrong. See the explanation for (5) below. (5) is correct. Assertion checking can be selectively enabled or disabled on a per-package basis. Note that the package default assertion status determines the assertion status for classes initialized in the future that belong to the named package or any of its "subpackages". The assertion status can be set for a named top-level class and any nested classes contained therein. This setting takes precedence over the class loader's default assertion status, and over any applicable per-package default. If the named class is not a top-level class, the change of status will have no effect on the actual assertion status of any class.

Question 4

Which statement is true?

Accepted Answer

Option A is correct. The assertion status can be set for a named top-level class and any nested classes contained therein. This setting takes precedence over the class loader's default assertion status, and over any applicable per-package default. If the named class is not a top-level class, the change of status will have no effect on the actual assertion status of any class. Option B is wrong. Is there such a thing as conditional compilation in Java? Option C is wrong. For private methods - yes. But do not use assertions to check the parameters of a public method. An assert is inappropriate in public methods because the method guarantees that it will always enforce the argument checks. A public method must check its arguments whether or not assertions are enabled. Further, the assert construct does not throw an exception of the specified type. It can throw only an AssertionError. Option D is wrong. Because you're never supposed to handle an assertion failure. That means don't catch it with a catch clause and attempt to recover.

Question 5

Which of the following statements is true?

Accepted Answer

Option A is correct because it is sometimes advisable to thrown an assertion error even if assertions have been disabled. Option B is incorrect because it is considered appropriate to check argument values in private methods using assertions. Option C is incorrect; finally is never bypassed. Option D is incorrect because AssertionErrors should never be handled.

Question 6

Which statement is true about assertions in the Java programming language?

Accepted Answer

Option A is correct. Because assertions may be disabled, programs must not assume that the boolean expressions contained in assertions will be evaluated. Thus these expressions should be free of side effects. That is, evaluating such an expression should not affect any state that is visible after the evaluation is complete. Although it is not illegal for a boolean expression contained in an assertion to have a side effect, it is generally inappropriate, as it could cause program behaviour to vary depending on whether assertions are enabled or disabled. Assertion checking may be disabled for increased performance. Typically, assertion checking is enabled during program development and testing and disabled for deployment. Option B is wrong. Because you assert that something is "true". True is Boolean. So, an expression must evaluate to Boolean, not int or byte or anything else. Use the same rules for an assertion expression that you would use for a while condition. Option C is wrong. Usually, enforcing a precondition on a public method is done by condition-checking code that you write yourself, to give you specific exceptions. Option D is wrong. "You're never supposed to handle an assertion failure" Not all legal uses of assertions are considered appropriate. As with so much of Java, you can abuse the intended use for assertions, despite the best efforts of Sun's Java engineers to discourage you. For example, you're never supposed to handle an assertion failure. That means don't catch it with a catch clause and attempt to recover. Legally, however, AssertionError is a subclass of Throwable, so it can be caught. But just don't do it! If you're going to try to recover from something, it should be an exception. To discourage you from trying to substitute an assertion for an exception, the AssertionError doesn't provide access to the object that generated it. All you get is the String message.

Assertions Questions