To answer this question, we need to understand the concept of method overriding in Java.

Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its parent class. When overriding a method, certain rules must be followed. Let's go through each option to understand why it is correct or incorrect:

Option A) The new method should return int - This option is incorrect. The return type of the overriding method can be a subtype of the return type of the overridden method, but it cannot be a different type.

Option B) The new method can return any type of values - This option is incorrect. The return type of the overriding method should be covariant with the return type of the overridden method. In other words, it should be the same type or a subtype of the return type of the overridden method.

Option C) The argument list of the new method should exactly match that of the overridden method - This option is correct. The argument list of the overriding method should be the same as the argument list of the overridden method. This ensures that the method signature remains the same.

Option D) The return type of the new method should exactly match that of the overridden method - This option is incorrect. As mentioned earlier, the return type of the overriding method can be a subtype of the return type of the overridden method, but it cannot be a different type.

The correct answer is C. The argument list of the new method should exactly match that of the overridden method. This ensures that the method signature remains the same.

Therefore, the correct answer is option C.

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• Wrong explanation

To answer this question, you need to understand the concept of converting a class into a thread in Java.

In Java, a class can be converted to a thread by implementing the Runnable interface. The Runnable interface defines a single method named run(), which is the entry point for the thread when it is started. By implementing this interface, the class can define the code that will be executed in a separate thread when the thread is started.

Option A) Thread - This option is incorrect because the Thread class itself represents a thread, rather than converting a class into a thread.

Option B) Runnable - This option is correct because implementing the Runnable interface allows a class to be converted into a thread by defining the run() method.

Option C) Both of these - This option is incorrect because only implementing the Runnable interface is required to convert a class into a thread. The Thread class is not necessary for this conversion.

Option D) none of these - This option is incorrect because implementing the Runnable interface is the correct way to convert a class into a thread.

The correct answer is Option B) Runnable. This option is correct because implementing the Runnable interface allows a class to be converted into a thread.

Therefore, the correct answer is B) Runnable.

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To answer this question, let's analyze the given code step by step:

TreeSet map = new TreeSet();
map.add("one");
map.add("two");
map.add("three");
map.add("four");
map.add("one");
Iterator it = map.iterator();
while (it.hasNext()) {
    System.out.print(it.next() + " ");
}

In this code, a TreeSet named map is created. A TreeSet is a collection that stores elements in a sorted and unique order.

The following elements are added to the map:

• "one"
• "two"
• "three"
• "four"
• "one" (Note that "one" is added again)

Next, an iterator named it is created using the iterator() method of the TreeSet. The iterator allows iterating over the elements in the TreeSet in a sequential manner.

The while loop is then used to iterate over the elements in the TreeSet using the iterator. The condition it.hasNext() checks if there are more elements to iterate over. If there are, the loop continues.

Inside the loop, it.next() is used to retrieve the next element from the TreeSet. This element is then printed using System.out.print().

Let's analyze the output of the code:

• The elements in the TreeSet are stored in a sorted order.
• Since "four" comes before "one" in alphabetical order, "four" is printed first.
• Next, "one" is printed.
• "three" comes before "two" in alphabetical order, so "three" is printed next.
• Finally, "two" is printed.

Therefore, the output of the code is: "four one three two".

The correct answer is D. "four one three two".

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To answer this question, you need to understand the concept of inheritance in object-oriented programming.

Option A) X extends Y is correct if and only if X is a class and Y is an interface - This option is incorrect because in Java, a class can extend another class or implement an interface. It is not limited to only extending classes and implementing interfaces.

Option B) X extends Y is correct if and only if X is an interface and Y is a class - This option is incorrect because in Java, a class can extend another class or implement an interface. It is not limited to only extending interfaces and implementing classes.

Option C) X extends Y is correct if X and Y are either both classes or both interfaces - This option is correct. In Java, a class can extend another class and implement multiple interfaces. Similarly, an interface can extend multiple interfaces. So, X extends Y is correct if both X and Y are either both classes or both interfaces.

Option D) X extends Y is correct for all combinations of X and Y being classes and/or interfaces - This option is incorrect because, as explained above, extending a class and implementing an interface are two different concepts in Java. The correct statement is that X extends Y is correct if both X and Y are either both classes or both interfaces.

The correct answer is Option C.

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• Wrong explanation