To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) many - This option is incorrect because the invade method in the Alien class has two overloaded versions: one that takes a short parameter and one that takes a variable number of short parameters. In this case, the invade method is called with a single int argument (7), so it does not match any of the available methods.

Option B) a few - This option is incorrect for the same reason as option A. The invade method that takes a single short parameter is not called, so this option is not the result.

Option C) Compilation fails. - This option is correct because there is no matching method in the Alien class for the invade method call with an int argument. The compiler will give an error indicating that the method call is ambiguous because it matches both the method with a short parameter and the method with a variable number of short parameters.

Option D) An exception is thrown at runtime - This option is incorrect because the code fails to compile, so it will not even reach the runtime stage. Therefore, no exception will be thrown at runtime.

The correct answer is C. Compilation fails. This option is correct because the method call does not match any of the available methods in the Alien class.

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• Wrong explanation

To determine the result of the given code, let's go through each option and explain why it is correct or incorrect:

Option A) 1 1 - This option is incorrect. The doX() method is overloaded with different parameter types, but none of the overloads accept a short as an argument.

Option B) 2 1 - This option is incorrect. The doX() method is overloaded with different parameter types, but the doX(long... x) overload is not applicable for the given arguments because a short cannot be automatically promoted to a long.

Option C) 3 1 - This option is incorrect. The doX() method is overloaded with different parameter types, but the doX(Integer x, Integer y) overload is not applicable for the given arguments because a short cannot be automatically boxed to an Integer.

Option D) 4 1 - This option is incorrect. The doX() method is overloaded with different parameter types, but the doX(Number n, Number m) overload is not applicable for the given arguments because a short cannot be automatically boxed to a Number.

Option E) 2 3 - This option is incorrect. The doX() method is overloaded with different parameter types, but the doX(long... x) overload is not applicable for the given arguments because a short cannot be automatically promoted to a long. However, the doX(Integer x, Integer y) overload is applicable and will be chosen.

Option F) 4 3 - This option is correct. The doX() method is overloaded with different parameter types, and both the doX(Number n, Number m) overload and the doX(Integer x, Integer y) overload are applicable for the given arguments. However, the doX(Number n, Number m) overload is more specific because it accepts Number parameters, which are the superclasses of Integer. Therefore, it will be chosen for the call doX(s, s). The call doX(7, 7) will choose the doX(Integer x, Integer y) overload.

The correct answer is option F) 4 3.

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• Wrong explanation

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) true true - This option is correct because it means that both the references f1 and f3 are pointing to the same object, and the value of x in that object is 6. So, (f1 == f3) is true because they refer to the same object and (f1.x == f3.x) is also true because the value of x is the same.

Option B) true false - This option is incorrect because (f1.x == f3.x) should be true since x is updated to 6 in the FizzSwitch method.

Option C) false true - This option is incorrect because (f1 == f3) should be true since f1 and f3 are referring to the same object.

Option D) false false - This option is incorrect because (f1 == f3) should be true since f1 and f3 are referring to the same object, and (f1.x == f3.x) should be true since x is updated to 6 in the FizzSwitch method.

Option E) Compilation fails - This option is incorrect because there are no compilation errors in the given code.

Option F) An exception is thrown at runtime - This option is incorrect because there are no exceptions thrown in the given code.

The correct answer is A. This option is correct because (f1 == f3) is true because they refer to the same object and (f1.x == f3.x) is also true because the value of x is the same.

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• Wrong explanation

To determine which lines will compile using Java 5 but not Java 1.4, let's analyze each line of code:

Line 4: long x1 = Long.valueOf("123"); This line will compile in both Java 5 and Java 1.4. The valueOf method returns a Long object, which can be assigned to a long variable.

Line 5: Long x2 = Long.valueOf("123"); This line will compile in both Java 5 and Java 1.4. Similar to line 4, the valueOf method returns a Long object, which can be assigned to a Long variable.

Line 6: long x3 = xL.longValue(); This line will compile in both Java 5 and Java 1.4. The longValue method returns a long value, which can be assigned to a long variable.

Line 7: Long x4 = xL.longValue(); This line will NOT compile in Java 1.4 but will compile in Java 5. In Java 1.4, the longValue method returns a long value, which cannot be directly assigned to a Long variable. In Java 5, it will automatically be boxed into a Long object.

Line 8: Long x5 = Long.parseLong("456"); This line will NOT compile in Java 1.4 but will compile in Java 5. In Java 1.4, the parseLong method returns a long value, which cannot be directly assigned to a Long variable. In Java 5, it will automatically be boxed into a Long object.

Line 9: long x6 = Long.parseLong("123"); This line will compile in both Java 5 and Java 1.4. The parseLong method returns a long value, which can be assigned to a long variable.

Based on the explanations above, the lines that will compile using Java 5 but will NOT compile using Java 1.4 are:

A. Line 4 D. Line 7 E. Line 8

Therefore, the correct answer is A, D, and E.

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• Wrong explanation

To answer this question, let's go through the code step by step:

1. We start by executing the main method in the Hawk class.
2. The first line in the main method is System.out.print("pre ");, which prints "pre ".
3. The next line is new Hawk();, which creates a new instance of the Hawk class.
4. Since Hawk extends Raptor, which extends Bird, the first thing that happens when we create a new instance of Hawk is the execution of the Bird constructor.
5. The Bird constructor contains an instance initializer block, which prints "bl ".
6. Then, the Bird constructor itself prints "b2 ".
7. After the Bird constructor is executed, we move on to the Raptor constructor.
8. Before the Raptor constructor, there is a static initializer block, which prints "r1 ".
9. Then, the Raptor constructor itself prints "r2 ".
10. Next, there is another instance initializer block in the Raptor class, which prints "r3 ".
11. Finally, there is another static initializer block in the Raptor class, which prints "r4 ".
12. After the Raptor constructor is executed, we move back to the Hawk constructor.
13. Since there are no instance initializer blocks in the Hawk class, we move directly to the Hawk constructor, which does not contain any print statements.
14. After the Hawk constructor is executed, we go back to the main method.
15. The last line in the main method is System.out.println("hawk ");, which prints "hawk ".

Based on the above explanation, the result will be:

D. r1 r4 pre b1 b2 r3 r2 hawk

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• Wrong explanation

To answer this question, we need to understand the purpose of flushing database buffers and how it is done.

Database buffers are used to temporarily store data in memory before writing it to the disk. Flushing the database buffers involves writing the data from the buffers to the disk, ensuring that the data is persistent and not lost in case of a system failure.

Among the given options, the correct command to flush the database buffers is:

A) $TAB - This option is correct because the $TAB command is commonly used to flush the database buffers. It forces the data in the buffers to be written to the disk, ensuring data durability.

B) $RESET - This option is incorrect because the $RESET command is not typically used to flush database buffers. The $RESET command is usually used to reset system configurations or parameters.

C) $INIT - This option is incorrect because the $INIT command is not commonly used to flush database buffers. The $INIT command is typically used for initializing or starting a process or system.

D) $FREE - This option is incorrect because the $FREE command is not typically used to flush database buffers. The $FREE command is usually used to release memory or resources that are no longer needed.

The correct answer is A) $TAB. This option is correct because the $TAB command is commonly used to flush the database buffers and ensure data durability.

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• Wrong explanation