Test

Quick check

1. 1. What is the correct way to declare a 2D array in Java?

   int[][] array = new int[][];int array[][] = new int[][];int[][] array = new int[3][3];int[3][3] array = new int[][];

2. 2. Which of the following is true about classes in Java?

   A class can have multiple constructorsA class can only have one constructorA class must have at least one constructorA class cannot have a constructor with parameters

3. 3. What is encapsulation in Java?

   The process of inheriting properties from a parent classThe bundling of data and methods that operate on that data within a single unitThe ability of an object to take on many formsThe process of creating a new instance of a class

4. 4. Which keyword is used to implement inheritance in Java?

   extendsimplementsinheritssuper

5. 5. What is polymorphism in Java?

   The ability to create multiple objectsThe ability to have multiple methods with the same nameThe ability of an object to take on many formsThe ability to restrict access to class members

6. 6. Which of the following is true about ArrayList in Java?

   ArrayList is a fixed-size data structureArrayList can only store primitive data typesArrayList implements the List interfaceArrayList elements can be accessed using square bracket notation

7. 7. What is recursion in Java?

   A method that calls itselfA loop that runs indefinitelyA way to create multiple instances of a classA method to sort elements in an array

8. 8. Which of the following is a correct way to initialize a 2D array in Java?

   int[][] array = {{1, 2}, {3, 4}, {5, 6}};int[][] array = [1, 2; 3, 4; 5, 6];int[][] array = new int[3]{1, 2, 3, 4, 5, 6};int[][] array = (1, 2), (3, 4), (5, 6);

9. 9. What is the purpose of the 'private' access modifier in Java?

   To make the member accessible only within the same packageTo make the member accessible only within the same classTo make the member accessible from any classTo make the member accessible only to subclasses

10. 10. Which of the following is true about method overriding in Java?

    The overriding method must have the same return type as the overridden methodThe overriding method can have a different access modifierThe overriding method can throw broader exceptions than the overridden methodThe overriding method must have the same method name and parameter list as the overridden method

11. 11. What is the output of the following code? ArrayList<String> list = new ArrayList<>(); list.add("A"); list.add("B"); list.add("C"); list.add(1, "D"); System.out.println(list);

    [A, B, C, D][A, D, B, C][D, A, B, C][A, B, D, C]

12. 12. Which of the following is true about abstract classes in Java?

    Abstract classes can be instantiatedAbstract classes can have both abstract and non-abstract methodsAll methods in an abstract class must be abstractAbstract classes cannot have constructors

13. 13. What is the purpose of the 'super' keyword in Java?

    To call the superclass constructorTo create a new instance of the superclassTo access the superclass membersBoth a and c

14. 14. Which of the following is true about the 'final' keyword in Java?

    A final class cannot be subclassedA final method cannot be overriddenA final variable cannot be reassignedAll of the above

15. 15. What is the correct way to declare a method that throws an exception in Java?

    public void myMethod() throws Exception { }public void myMethod() throw Exception { }public void myMethod() : Exception { }public void myMethod() exception { }

16. 16. Which of the following is NOT a valid way to iterate over an ArrayList in Java?

    for (int i = 0; i < list.size(); i++) { }for (String item : list) { }list.forEach(item -> { });while (list.hasNext()) { }

17. 17. What is the output of the following recursive method call? public static int mystery(int n) { if (n == 0) return 0; return n + mystery(n - 1); } System.out.println(mystery(5));

    5101520

18. 18. Which of the following is true about interfaces in Java?

    Interfaces can have instance variablesA class can implement multiple interfacesInterfaces can have constructorsAll methods in an interface are concrete

19. 19. What is the purpose of the 'instanceof' operator in Java?

    To create a new instance of a classTo check if an object is an instance of a specific class or interfaceTo compare two objects for equalityTo check if a class is a subclass of another class

20. 20. Which of the following is true about method overloading in Java?

    Overloaded methods must have different return typesOverloaded methods must have different access modifiersOverloaded methods must have different parameter listsOverloaded methods must be in different classes