| No. | Answer | Remark | |
|---|---|---|---|
| 1 | d | Prints: true,true | Both Error and Exception are subclasses of Throwable. |
| 2 | a d | class A extends Object. Compile-time error at 3. | The constructors for class B and class C both invoke the constructor for A. The constructor for class A declares Exception in the throws clause. Since the constructors for B and C invoke the constructor for A, it is necessary to declare Exception in the throws clauses of B and C. A compile-time error is generated at marker 3, because the constructor does not declare Exception in the throws clause. |
| 3 | c | Prints: v w x x y z z | Cases one and three have no break statement, so the next case is also executed and x and z are printed twice. |
| 4 | b | Prints: false,true | Error is a direct subclass of Throwable. RuntimeException is a direct subclass of Exception. |
| 5 | e | Compile-time error. | The keyword, case, is missing from the case labels. |
| 6 | b | Prints: 0,0,1,1,0,1 | The nested catch clause is able to catch a Level2Exception or any subclass of it. The switch statement throws a Level1Exception that can not be caught by the nested catch clause; so the nested finally block is executed as control passes to the first of the two outer catch clauses. The outer finally block is executed as control passes out of the try statement. |
| 7 | c | Prints: 0,1,1,0,0,1 | The nested catch block is able to catch a Level2Exception or any subclass of it causing b to be incremented. Both of the finally blocks are then executed. |
| 8 | b | Prints: 0,1,1,0,0,1 | The nested catch block is able to catch a Level2Exception or any subclass of it causing b to be incremented. Both of the finally blocks are then executed. |
| 9 | d | Prints: 0,0,1,0,1,1 | The nested catch clause is able to catch a Level2Exception or any subclass of it. The switch statement throws an Exception that can not be caught by the nested catch clause; so the nested finally block is executed as control passes to the second of the two outer catch clauses. The outer finally block is executed as control passes out of the try statement. |
| 10 | b | Prints: 1,0,1,0,0,1 | The switch statement does not throw an exception; so the switch completes normally. The subsequent statement increments the variable, a; and the try block completes normally. Both of the finally blocks are then executed. |
| 11 | b e | With assertions enabled it prints 210210 followed by an AssertionError message. With assertions disabled it prints 210210-1 | If, under normal operating circumstances, the default label of a switch statement should not be reached, then an assert statement can be placed after the default label to verify that an unexpected condition has not not occurred. |
| 12 | b e g | With assertions enabled it prints 012. With assertions disabled it attempts to print an infinite sequence of numbers. As a rule, the boolean expression of an assert statement should not be used to perform actions that are required for normal operation of the program. | An assert statement should not be used as demonstrated in the program. The boolean expression of the do-loop depends on the value of the local variable i1. The value of i1 is set within the boolean expression of the assert statement. If assertions are disabled, then the boolean expression of the assert statement is not processed and the value of i1 is not updated with each iteration of the loop; so the loop runs indefinitely. |
| 13 | a d | Assertions should not be used to validate arguments passed to public methods. Assertions should not be used to perform processing that is required for the normal operation of the application. | Assertions may be enabled or disabled at run time. Since assertions are not always enabled, they should not be used to validate the parameters of public methods. Parameter checking is typically published in the API specification of a method and must be enforced even when assertions are not enabled. Rather than use an assertion, an appropriate runtime exception should be thrown such as IllegalArgumentException, IndexOutOfBoundsException, or NullPointerException. However, an assertion may be used to validate the parameters of a nonpublic method. Since assertions are not always enabled, an assertion should not be used to perform operations that are required for the normal operation of the program. For example, the boolean expression of an assertion should not be used to produce the side effect of incrementing a variable that controls a loop statement. If assertions are disabled then the loop is unlikely to function as intended. Section 14.20 of the Java Language Specification defines "unreachable" statements. If an assert statement is "unreachable" as defined by the JLS, then a compile-time error is generated. In contrast, a programmer may believe that some points in the code will not be reached as a result of design assumptions. For example, a programmer may believe that the default case of a switch statement will never be reached. An assertion can be placed in the default case to verify the behavior of the switch statement. |
| 14 | b c | The compiler will generate an error if an assert statement is "unreachable" as defined by the Java Language Specification. A catch clause should not be used to catch an AssertionError. | Section 14.20 of the Java Language Specification defines "unreachable" statements. If an assert statement is "unreachable" as defined by the JLS, then a compile-time error is generated. In contrast, a programmer may believe that some points in the code will not be reached as a result of design assumptions. For example, a programmer may believe that the default case of a switch statement will never be reached. An assertion can be placed in the default case to verify the behavior of the switch statement. While the exception handling mechanisms of Java have been designed to allow for recovery from Exceptions, the assertion mechanisms have been designed to discourage recovery attempts. An assertion is used to verify that the program has not strayed beyond the bounds of expected behavior. For example, suppose that you go to bed one night, and your pet dog is sleeping on the floor next to your bed. Before going to sleep, you make the assertion that your dog will still be there in the morning. When you wake up, you find that a different dog is sleeping in place of your pet. How do you recover from the failure of your assertion? Since you probably did not expect your dog to be mysteriously replaced during the night, it is unlikely that you have already developed an effective recovery routine. However, if you had planned for a dog swapping exception, then the recovery should be handled by the exception handling mechanism rather than the assertion mechanism. |
| 15 | f | Compile-time error | The case constant expression, 1000, produces a compile-time error, because it exceeds the range of the switch expression type, byte. The type of a switch expression can be byte, short, int or char. A constant expression is associated with each case label. Each case constant expression must be assignable to the type of the switch expression. In this case, the switch expression, b, is of type byte; so the maximum positive value of each case constant expression is limited to the maximum byte value, 127. |
| 16 | a b d | With assertions enabled it prints ABC followed by an AssertionError message. With assertions disabled it prints ABC followed by an AssertionError message. In this code example an assert statement could not be used in place of the "throw" statement. | If the default label of a switch statement should not be reached under normal operating circumstances, then the default label might be a good location for an assert statement. If a method is declared with a non-void return type and if no return statement appears after the switch statement, then each case of the switch must have a return statement or a throw statement. The throw statement is used rather than an assert, because the compiler knows that the assert statement is not functional when assertions are disabled. |
| 17 | c | Prints: 234 | No break statements appear inside the switch statement, so more than one case is processed. |
| 18 | a d | With assertions enabled it prints ABC followed by an AssertionError message. With assertions disabled it prints ABCE | If the default label of a switch statement should not be reached under normal operating circumstances, then the default label might be a good candidate for the use of an assert statement. |
| 19 | c | Prints: 61433 | On the first pass through the loop, the value of x is 6, so 5 is subtracted from x. On the second pass, the value of x is 1, so 3 is added to x. On the third pass, the value of x is 4, so 1 is subtracted from x. On the fourth pass, the value of x is 3, so the variable, success, is incremented from zero to one. On the final pass, the value of x is 3 and the variable, success, is incremented to the value, 2. The boolean expression of the do loop is now false, so control passes out of the loop. |
| 20 | d e | In this code example a throw statement must be used in place of the assert statement. Compile-time error | If the default label of a switch statement should not be reached under normal operating circumstances, then the default case becomes a good candidate for the use of an assert statement. If a method is declared with a non-void return type and if no return statement appears after the switch statement, then each case of the switch must have a return statement or a throw statement. The throw statement is used rather than an assert, because the compiler knows that the assert statement is not functional when assertions are disabled. |
| 21 | b | Prints: 1433 | On the first pass through the loop, the switch expression, x, has the value, -5. None of the case constants are matched, so the statement following the default label is executed causing the value of x to be set to -3. On the second pass, the default case of the switch statement is executed again, and two is again added to the value of x. The new value is -1. On the third pass, the value of x is again incremented, and the new value is +1. After that, the value of x is printed on each pass through the loop. For the last two passes, the value of x is 3. |
| 22 | d | Run-time error | The index, i, is incremented before the array access expression is evaluated, so the first element accessed is at index one instead of zero. The arguments, BCDEF, are printed before an ArrayIndexOutOfBoundsException is thrown when the attempt is made to access an element beyond the end of the array. |