java - Arrays, Arraylist, vectors, wrapper class

What does array.length return?

• The memory size of the array

• The last element of the array

• The number of elements in the array

• The first element of the array

What is the output of the following code?

int[] numbers = {1, 2, 3, 4, 5};

System.out.println(numbers[2]);

• 1

• 2

• 3

• 4

Which of the following is the correct way to instantiate a 2x3 (2 rows, 3 columns) two-dimensional array in Java?

• int[][] array = new int[2][3];

• int array[][] = {{1, 2, 3}, {4, 5, 6}};

• int[] array = new int[2, 3];

• Both A and B

What is the output of the following Java code?

int[][] numbers = {{1, 2}, {3, 4}, {5, 6}};

System.out.println(numbers[1][1]);

• 1

• 2

• 3

• 4

What is a Vector in Java?

• A fixed-size collection of elements
  

• A dynamic array that can grow or shrink in size
  

• A collection that allows duplicate and does not preserve the insertion order
  

• A high-performance, thread-safe collection designed for multi-threaded access

How can you remove an element from a Vector?

• Using the delete(int index) method

• Using the removeElement(Object obj) method

• Using the remove(int index) method

• Both B and C are correct

What is the purpose of Wrapper classes in Java?

• To provide a way to use primitive data types as objects.

• To enhance the performance of collections that store objects.

• To provide a mechanism for synchronizing primitive data types.

• To allow primitive data types to be used in generic collections.

What is the output of the following code?

Integer a = 127;

Integer b = 127;

System.out.println(a == b);

• true
  

• false
  

• Compilation error
  

• An exception is thrown

What is an ArrayList in Java?

• A static array that cannot change its size.

• A dynamic array that can grow or shrink in size.

• A linked list implementation.

• A high-performance, thread-safe collection.

What is the result of calling size() method on an ArrayList that contains 5 elements?

• 4

• 5

• 6

• It throws an IndexOutOfBoundsException.