Java Mastery Challenge

What is the main principle of object-oriented programming?

• Inheritance of properties from a parent class.

• Encapsulation of data and behavior into objects.

• Static typing of all variables in the program.

• Polymorphism through method overloading only.

Explain the difference between an interface and an abstract class in Java.

• An interface can have instance variables, while an abstract class cannot.

• An abstract class can be instantiated, but an interface cannot.

• An interface can extend multiple classes, while an abstract class can only extend one.

• An interface defines a contract for classes to implement, while an abstract class can provide some method implementations and state.

What is the time complexity of accessing an element in an ArrayList?

• O(log n)

• O(n)

• O(n^2)

• O(1)

Describe the concept of inheritance in Java with an example.

• class Vehicle { void start() { System.out.println('Vehicle started'); } } class Car extends Vehicle { void start() { System.out.println('Car is running'); } }

• class Plant { void grow() { System.out.println('Plant growing'); } } class Tree extends Plant { void grow() { System.out.println('Tree is tall'); } }

• class Animal { void makeSound() { System.out.println('Meow'); } } class Cat extends Animal { void makeSound() { System.out.println('Roar'); } }

• Example: class Animal { void makeSound() { System.out.println('Animal sound'); } } class Dog extends Animal { void makeSound() { System.out.println('Bark'); } }

What is the purpose of the 'final' keyword in Java?

• The 'final' keyword is used to create interfaces.

• The 'final' keyword allows multiple inheritance in classes.

• The 'final' keyword is used to define abstract classes.

• The 'final' keyword is used to declare constants, prevent method overriding, and prevent inheritance.

How do you implement a stack using an array in Java?

• Implement the stack using a HashMap.

• Create a class with only a push method.

• Use a linked list to implement the stack.

• Create a class with an array, a top index, and methods for push, pop, and peek.

What is polymorphism and how is it achieved in Java?

• Polymorphism is achieved through the use of interfaces only.

• Polymorphism is the ability to create multiple classes in Java.

• Polymorphism allows objects to be created without any methods.

• Polymorphism is the ability of an object to take on many forms, achieved in Java through method overriding and method overloading.

Explain the difference between a HashMap and a TreeMap in Java.

• HashMap and TreeMap are both ordered and do not allow null values.

• HashMap does not allow null values; TreeMap allows null keys and is unordered.

• HashMap is ordered and allows null keys; TreeMap is unordered and allows null values.

• HashMap is unordered and allows null values; TreeMap is ordered and does not allow null keys.

What is the significance of the 'static' keyword in Java?

• The 'static' keyword allows for instance-specific variables.

• The 'static' keyword indicates that a method can be overridden.

• The 'static' keyword signifies that a member belongs to the class rather than any instance.

• The 'static' keyword is used to define abstract classes.

How do you perform a binary search on a sorted array in Java?

• Use a loop to adjust 'left' and 'right' pointers based on comparisons until the target is found or the pointers cross.

• Sort the array before performing the search.

• Use recursion to search through the entire array without pointers.

• Check each element sequentially until the target is found.