What is the output of the following Java code snippet?

• 5, 5

• 5, 10

• 10, 5

• 10, 10

Answer explanation

This Java code snippet defines a class with an integer variable x and creates two instances of the class. The second instance modifies the value of x to 10, but the first instance retains its original value of 5. The output of this code will be "5, 10".

What is the difference between "==" and ".equals()" in Java?

• There is no difference - they both compare the contents of two objects

• ".equals()" compares object references, while "==" compares the contents of the objects.

• "==" compares object references, while ".equals()" compares the contents of the objects.

• None of the above.

Answer explanation

The "==" operator in Java compares object references - that is, it checks to see if two variables are pointing to the exact same object in memory. The ".equals()" method, on the other hand, compares the contents of two objects to see if they are equal.

What is the output of the following Java code snippet?

• a = 10, b = 15

• a = 5, b = 10

• a = 15, b = 5

• a = 10, b = 5

Answer explanation

This code snippet uses the XOR operator to swap the values of the a and b variables without using a temporary variable. The output of this code will be "a = 10, b = 5".

What is the difference between an abstract class and an interface in Java?

• An abstract class can be extended by multiple classes, while an interface can only be implemented by a single class.

• An abstract class can have method implementations, while an interface cannot.

• An interface can have method implementations, while an abstract class cannot.

• An interface can be extended by multiple interfaces, while an abstract class can only be extended by a single class.

Answer explanation

An abstract class can have method implementations, while an interface cannot. However, both abstract classes and interfaces can define method signatures that must be implemented by any subclass or implementing class.

What is the output of the following JavaScript code?

• 10

• 20

• undefined

• ReferenceError

Answer explanation

In JavaScript, variables declared with "const" and "let" are block-scoped, which means they are only accessible within the block of code they were declared in. In this case, the "x" variable inside the "foo" function is declared with "const" after it is referenced in the console.log statement. This results in a ReferenceError, as the "x" variable is not yet defined in the function.

What is the purpose of the "useEffect" hook in React?

• It is used to manage the component's state

• It is used to fetch data from an API

• It is used to perform side effects within a component

• It is used to render the component to the DOM

Answer explanation

In React, the "useEffect" hook is used to perform side effects within a component. Side effects are actions that occur outside of the normal rendering process, such as fetching data from an API or manipulating the DOM. The "useEffect" hook takes a function as its argument and runs it after every rendering cycle. This hook can also be used to clean up any side effects when the component is unmounted.

What is the output of the following React code?

• The code will not work because the function is not written properly.

• The code will render a button with the text "Click me" on the page.

• The code will render a button with the text "Click me" on the page and log "Button clicked!" to the console when the button is clicked.

• The code will render a button with the text "Button clicked!" on the page when the button is clicked.

Answer explanation

The handleClick function is defined using an arrow function and passed as a prop to the button's onClick event handler. When the button is clicked, the handleClick function is called, which logs "Button clicked!" to the console.

Which of the following is a valid way to declare a function in JavaScript?

• function myFunction = () => {}

• let myFunction = function() {}

• const myFunction() => {}

• myFunction: function() {}

Answer explanation

Option a) is using an arrow function syntax which is a valid way to declare a function, but it is assigning the function to a variable using the equal sign instead of the keyword function.

Option c) is also using an arrow function syntax, but it is missing the equal sign before the arrow, which would result in a syntax error.

Option d) is using object literal notation, not function declaration syntax. The correct way to declare a function in object literal notation is using a colon like this:

Which of the following data structures is based suited to implement a priority queue?

• Array

• Stack

• Binary Heap

• Queue

Answer explanation

A priority queue is a data structure in which each element has a priority associated with it, and the element with the highest priority is always at the front of the queue. A binary heap is a tree-based data structure that can be used to implement a priority queue efficiently. In a binary heap, the highest priority element is always at the root of the tree. While it is technically possible to implement a priority queue using array data structure, the resulting implementation would not be efficient.

Which of the following data structures is best suited for implementing a LIFO stack?

• Linked list

• Queue

• Array

• Tree

Answer explanation

A linked list is the best data structure for implementing a LIFO stack because it allows for efficient insertion and deletion operations at the beginning of the list, which corresponds to the top of the stack. The other options (queue, array, and tree) do not have the same level of efficiency for these operations.