visual basic barcode program Do use assertions to validate arguments to a private method. in Java

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Do use assertions to validate arguments to a private method.
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If you write a private method, you almost certainly wrote (or control) any code that calls it. When you assume that the logic in code calling your private method is correct, you can test that assumption with an assert as follows:
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private void doMore(int x) { assert (x > 0); // do things with x }
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The only difference that matters between the preceding example and the one before it is the access modifier. So, do enforce constraints on private arguments, but do not enforce constraints on public methods. You re certainly free to compile assertion code with an inappropriate validation of public arguments, but for the exam (and real life) you need to know that you shouldn t do it.
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Do not use assertions to validate command-line arguments.
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This is really just a special case of the Do not use assertions to validate arguments to a public method rule. If your program requires command-line arguments, you ll probably use the exception mechanism to enforce them.
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Working with the Assertion Mechanism (Exam Objectives 2.4 and 2.5)
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Do use assertions, even in public methods, to check for cases that you know are never, ever supposed to happen.
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This can include code blocks that should never be reached, including the default of a switch statement as follows:
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switch(x) { case 2: y = 3; case 3: y = 17; case 4: y = 27; default: assert false; // We're never supposed to get here! }
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If you assume that a particular code block won t be reached, as in the preceding example where you assert that x must be either 2, 3, or 4, then you can use assert false to cause an AssertionError to be thrown immediately if you ever do reach that code. So in the switch example, we re not performing a boolean test we ve already asserted that we should never be there, so just getting to that point is an automatic failure of our assertion/assumption.
Do not use assert expressions that can cause side effects!
The following would be a very bad idea:
public void doStuff() { assert (modifyThings()); // continues on } public boolean modifyThings() { x++ = y; return true; }
The rule is: An assert expression should leave the program in the same state it was in before the expression! Think about it. Assert expressions aren t guaranteed to always run, so you don t want your code to behave differently depending on whether assertions are enabled. Assertions must not cause any side effects. If assertions are enabled, the only change to the way your program runs is that an AssertionError can be thrown if one of your assertions (think: assumptions) turns out to be false.
4: Flow Control, Exceptions, and Assertions
CERTIFICATION SUMMARY
This chapter covered a lot of ground, all of which involves ways of controlling your program flow, based on a conditional test. First you learned about if and switch statements. The if statement evaluates one or more expressions to a boolean result. If the result is true, the program will execute the code in the block that is encompassed by the if. If an else statement is used and the expression evaluates to false, then the code following the else will be performed. If the else is not used, then none of the code associated with the if statement will execute. You also learned that the switch statement is used to replace multiple if-else statements. The switch statement can evaluate only integer primitive types that can be implicitly cast to an int. Those types are byte, short, int, and char. At runtime, the JVM will try to find a match between the argument to the switch statement and an argument in a corresponding case statement. If a match is found, execution will begin at the matching case, and continue on from there until a break statement is found or the end of the switch statement occurs. If there is no match, then the default case will execute, if there is one. You ve learned about the three looping constructs available in the Java language. These constructs are the for loop, the while loop, and the do-while loop. In general, the for loop is used when you know how many times you need to go through the loop. The while loop is used when you do not know how many times you want to go through, whereas the do-while is used when you need to go through at least once. In the for loop and the while loop, the expression will have to evaluate to true to get inside the block and will check after every iteration of the loop. The do-while loop does not check the condition until after it has gone through the loop once. The major benefit of the for loop is the ability to initialize one or more variables and increment or decrement those variables in the for loop definition. The break and continue statements can be used in either a labeled or unlabeled fashion. When unlabeled, the break statement will force the program to stop processing the innermost looping construct and start with the line of code following the loop. Using an unlabeled continue command will cause the program to stop execution of the current iteration of the innermost loop and proceed with the next iteration. When a break or a continue statement is used in a labeled manner, it will perform in the same way, with one exception. The statement will not apply to the innermost loop; instead, it will apply to the loop with the label. The break statement is used most often in conjunction with the switch statement.
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