Interview questions 3

Question 1

public access modifier meaning in Java

Answer 1

Can be accessed by other classes

Question 2

private access modifier meaning in Java

Answer 2

Cannot be accessed by other classes

Question 3

protected access modifier meaning in Java

Answer 3

Declarations are visible within the package or all subclasses

Question 4

Default access modifier in Java

Answer 4

Declarations are visible only within the package (package private)

Question 5

Reason for not using public access mods

Answer 5

You would have to be careful when you make changes to it, because you never know which parts of the codebase rely on its exact behavior.

Question 6

Reason to use private access mods

Answer 6

There is a lot less code you have to pay attention to when you make changes.

Question 7

What is a wrapper class?

Answer 7

Wrapper classes provide a way to use primitive data types (int, char, short, byte, etc) as objects.

Question 8

Purpose of a wrapper class.

Answer 8

Wrapper Class will convert primitive data types into objects. The objects are necessary if we wish to modify the arguments passed into the method (because primitive types are passed by value).

Question 9

What does a helper class do?

Answer 9

Provides common methods which are required by multiple classes in the project.

Question 10

How many classes (superclass) can a class extend?

Answer 10

Only one.

Question 11

Difference between hashset & list.

Answer 11

In hashset, no duplicates are allowed, and it is unordered.

Question 12

What is decoupling & benefits?

Answer 12

Making components as independent as possible from one another. Makes code easier to understand.

Question 13

Why is polymorphism desirable & what are some drawbacks?

Answer 13

Helps with reusability of code and makes it easier to read.

Question 14

4 pillars of oop.

Answer 14

• abstraction
• encapsulation
• inheritance
• polymorphism

Question 15

stack vs heap.

Answer 15

stack = linear, heap = hierarchical. Stack = rigid, heap = flexible/ Stack is safer because the data stored can only be access by owner thread, not by all threads like heap memory.

Question 16

What is abstraction?

Answer 16

Hide the implementation details of something so that when you call a function you only have to know what it does, not how it does it.

Question 17

what is encapsulation?

Answer 17

In encapsulation, the variables or data of a class is hidden from any other class and can be accessed only through any member function of its own class in which it is declared. Another way to think about encapsulation is, that it is a protective shield that prevents the data from being accessed by the code outside this shield. Use private vars in class or make var only accessible through getters & setters.