Key Points:

1. Array Creation and Access (6.1)
• Arrays are used to store multiple values in a single variable.
• Arrays are indexed starting at 0.
• 1D Array can be created by specifying the size and data type.
• ArrayList is a dynamic array that can grow in size as elements are added.
• Basic operations: creating, accessing elements, updating, and traversing arrays.

2. Traversing Arrays (6.2)
• Traversing refers to iterating over each element of the array.
• It’s typically done using a loop (for, while).
• Arrays and ArrayLists can be manipulated by modifying elements in the loop.
• Errors in code can often stem from incorrect indexing, out-of-bound access, or improper initialization.

Sample Code:

20 AP-style MCQs (without answers):

1. Which of the following statements correctly creates an array of 5 integers?
• A) int[] arr = {1, 2, 3, 4, 5};
• B) int[] arr = new int[5];
• C) int arr[5] = {1, 2, 3, 4, 5};
• D) Both A and B

2. What is the index of the last element in the array int[] arr = {10, 20, 30, 40, 50};?
• A) 5
• B) 4
• C) 3
• D) 0

3. What will the following code output?
• A) 5
• B) 10
• C) 15
• D) Error

4. Which of the following statements is true about ArrayLists in Java?
• A) They have a fixed size after initialization.
• B) They can hold elements of any type, including primitives.
• C) They are dynamic in size and can grow as needed.
• D) ArrayLists can only hold Integer objects.

5. What is the output of the following code?
• A) 200
• B) 100
• C) Error
• D) null

6. What will happen if you try to access arr[10] in the following code?
• A) It will print 0.
• B) It will throw an ArrayIndexOutOfBoundsException.
• C) It will print null.
• D) It will print 10.

7. Which of the following methods can be used to traverse an ArrayList?
• A) for (int i = 0; i < list.size(); i++)
• B) for (int i : list)
• C) list.forEach(element -> System.out.println(element));
• D) All of the above

8. What is the correct way to create an ArrayList of Strings?
• A) ArrayList<String> list = new ArrayList<>();
• B) ArrayList<String> list = new ArrayList[10];
• C) String[] list = new String[10];
• D) ArrayList<String> list = new ArrayList();

9. How do you access the second element of an ArrayList list?
• A) list[1]
• B) list.get(1)
• C) list(1)
• D) list[2]

10. What is the result of the following code?
• A) 2
• B) 6
• C) 8
• D) Error

11. Which of the following statements is incorrect about arrays?
• A) Arrays in Java are fixed in size once they are initialized.
• B) Arrays in Java can hold primitive data types.
• C) Arrays can hold multiple types of data at once.
• D) Arrays are indexed starting at 0.

12. What will happen if you attempt to access an index out of bounds in an array?
• A) The program will crash immediately.
• B) An ArrayIndexOutOfBoundsException will be thrown.
• C) The program will print the value of index 0.
• D) The program will print null.

13. How can you initialize an array with 10 elements of type int?
• A) int[] arr = new int[10];
• B) int arr[] = new int[10];
• C) int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
• D) All of the above

14. Which of the following will cause a compilation error?
• A) int[] arr = new int[5];
• B) ArrayList<String> list = new ArrayList<>();
• C) ArrayList list = new ArrayList<String>();
• D) int[] arr = {1, 2, 3, 4};

15. What is the default value of an integer element in an array?
• A) 0
• B) null
• C) undefined
• D) Error

16. Which of the following code segments correctly creates and manipulates an array of 5 integers?
• A) int[] nums = {1, 2, 3, 4, 5};
• B) int nums[] = new int[5]; nums[0] = 10;
• C) Both A and B
• D) None of the above

17. Which of the following operations is invalid for an ArrayList?
• A) list.add(10);
• B) list.remove(2);
• C) list[0] = 100;
• D) list.size();

18. Which of the following is true about the ArrayList list in Java?
• A) It can be resized dynamically.
• B) It can only hold Integer objects.
• C) It can hold both primitive types and objects.
• D) It does not support element removal.

19. What will happen if you try to access an element using an invalid index in an ArrayList?
• A) It will return null.
• B) It will throw an IndexOutOfBoundsException.
• C) It will print the last element.
• D) It will print an empty string.

20. What is the correct syntax for initializing an array of 10 integers?
• A) int[] arr = new int[10];
• B) int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
• C) int arr[10];
• D) A and B