{"id":1229,"date":"2021-10-23T18:01:26","date_gmt":"2021-10-23T18:01:26","guid":{"rendered":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/2021\/10\/23\/sdet-interview-questions-part-3\/"},"modified":"2021-10-23T18:01:26","modified_gmt":"2021-10-23T18:01:26","slug":"sdet-interview-questions-part-3","status":"publish","type":"post","link":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/2021\/10\/23\/sdet-interview-questions-part-3\/","title":{"rendered":"Top SDET Interview Questions in Java – Part 3"},"content":{"rendered":"

<\/p>\n

\n

\n

\n

\n

<\/div>\n

\n

\n

<\/div>\n<\/div>\n

<\/div>\n

\n

<\/div>\n

\n

\n

table of contents<\/div>\n<\/p><\/div>\n<\/div>\n<\/div>\n

\n

\n

<\/div>\n

\n

\n

\n

1. How can we achieve Pass by value and pass by reference in Java?<\/a><\/div>\n

2. Explain Different types of interfaces in the Collection framework<\/a><\/div>\n

3. What is the difference between Array List and LinkedList? Which is better explain?<\/a><\/div>\n

4. What is the difference between List and Set?<\/a><\/div>\n

5. What is the difference between HashSet and HashMap?<\/a><\/div>\n

6. Explain Collection and Collections in Java?<\/a><\/div>\n

7. Explain the difference between Comparable and Comparator.<\/a><\/div>\n

8. Are Array and Array List are the same? If Not, How do we convert them to each other?<\/a><\/div>\n

9. What is Generic Class? Could you explain with a small snippet?<\/a><\/div>\n

10. How Sub Class is different from Inner Class?<\/a><\/div>\n

11. What is a singleton class? Explain with a small code snippet<\/a><\/div>\n

12. Explain Thread life cycle briefly? What are some commonly used methods?<\/a><\/div>\n

13. What is garbage collection? How to force Garbage Collection?<\/a><\/div>\n

Course Alert<\/a><\/div>\n<\/div>\n

<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

1. How can we achieve Pass by value and pass by reference in Java?<\/a><\/h3>\n
If we consider primitive types in a method, it is always pass by value.<\/p>\n
\n

\n<\/ins>\n<\/div>\n
For non-primitive types, it is always references (Object, Class)<\/p>\n
Consider Non-Primitive<\/strong> Types we can explain how value changes.<\/p>\n
Pass by Value like behavior can be achieved by assigning reference<\/p>\n
Example Code Snippet : Pass by value like behavior<\/strong>
<\/div>\n
\n
<\/div>\n
\n
\n
\/\/ Works like pass by value<\/span><\/p>\n
class Test<\/span><\/p>\n
{<\/span><\/p>\n
\u00a0\u00a0\u00a0 int x;<\/span><\/p>\n
\u00a0\u00a0\u00a0 Test(int i) { x = i; }<\/span><\/p>\n
\u00a0\u00a0\u00a0 Test()\u00a0\u00a0\u00a0\u00a0\u00a0 { x = 0; }<\/span><\/p>\n
}<\/span><\/p>\n
public class Main<\/span><\/p>\n
{<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String[] args)<\/span><\/p>\n
\u00a0\u00a0\u00a0 {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ t is a reference<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Test t = new Test(5);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Reference is passed and a copy of reference<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ is created in change()<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 change(t);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(t.x);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void change(Test t)<\/span><\/p>\n
\u00a0\u00a0\u00a0 {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 t = new Test(); \/\/ Changes doesn’t reflect, since assigning reference<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 t.x = 10;<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
\/\/Output:5<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
Example Code Snippet : Pass by Reference behavior can be achieved if we don\u2019t assign the reference<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
\/\/ Behaves like pass by reference<\/span><\/p>\n
class Test<\/span><\/p>\n
{<\/span><\/p>\n
\u00a0\u00a0\u00a0 int x;<\/span><\/p>\n
\u00a0\u00a0\u00a0 Test(int i) { x = i; }<\/span><\/p>\n
\u00a0\u00a0\u00a0 Test()\u00a0\u00a0\u00a0\u00a0\u00a0 { x = 0; }<\/span><\/p>\n
}<\/span><\/p>\n
public class Main<\/span><\/p>\n
{<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String[] args)<\/span><\/p>\n
\u00a0\u00a0\u00a0 {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ t is a reference<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Test t = new Test(5);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Reference is passed and a copy of reference<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ is created in change()<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 change(t);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(t.x);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void change(Test t)<\/span><\/p>\n
\u00a0\u00a0\u00a0 {<\/span><\/p>\n
\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0 t.x = 10; \/\/Changes reflects since we are not assigning t (refer first example)<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
\/\/Output: 10<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
2. Explain Different types of interfaces in the Collection framework<\/a><\/h3>\n
Note:<\/strong> The answer to this question is lengthy, Interviewer might ask few collections or all. To make it easier for you, we have given a short answer here with bullet points.<\/em><\/p>\n
$\"\"$ <\/em><\/p>\n<\/div>\n
\n
(You do not have to draw this diagram in the interview, this is for your easy understanding)<\/em><\/p>\n
The Collection in Java<\/strong> is a framework that provides an architecture to store and manipulate a group of objects. Java collection makes easier perform operation like searching, sorting and manipulate data.<\/p>\n
\n
Java util package contains the collection related classes and interfaces<\/li>\n<\/ul>\n
Collection Interfaces in Java.<\/p>\n
Iterable Interface<\/strong><\/p>\n
The Iterable interface is the root interface for all the collection classes<\/p>\n
Collection Interface<\/strong><\/p>\n
The Collection interface is the interface that is implemented by all the classes in the collection framework<\/p>\n
List Interface<\/strong><\/p>\n
\n
List interface is the subinterface of the Collection interface<\/strong><\/li>\n
ArrayList<\/strong><\/li>\n
The ArrayList class implements the List interface<\/li>\n
The ArrayList Uses a dynamic array to store the duplicate element of different data types<\/li>\n
The ArrayList maintains the insertion order<\/li>\n
The ArrayList can be randomly accessed<\/li>\n
The ArrayList is not synchronized<\/li>\n
LinkedList<\/strong><\/li>\n
Uses doubly linked list internally to store the elements<\/li>\n
It can store the duplicate elements<\/li>\n
It maintains the insertion order<\/li>\n
It is not synchronized<\/li>\n
Vector<\/strong><\/li>\n
Similar to ArrayList but synchronized<\/li>\n
Stack<\/strong><\/li>\n
Sub class of vector<\/li>\n
It implements the last-in-first-out data structure<\/li>\n<\/ul>\n
Queue Interface<\/strong><\/p>\n
Queue interface maintains the first-in-first-out order, it is an ordered list that is used to hold the elements which are about to be processed<\/p>\n
\n
PriorityQueue<\/strong><\/li>\n
PriorityQueue class implements the Queue interface<\/li>\n
It holds the elements or objects which are to be processed by their priorities<\/li>\n
It doesn’t allow null values<\/li>\n<\/ul>\n
Deque Interface<\/strong><\/p>\n
Deque interface extends the Queue interface, We can remove and add the elements from both the side, it helps us to perform the operations at both the ends.<\/p>\n
\n
ArrayDeque<\/strong><\/li>\n
ArrayDeque class implements the Deque interface<\/li>\n
It facilitates us to use the Deque<\/li>\n
We can add or delete the elements from both ends.<\/li>\n<\/ul>\n
Set Interface<\/strong><\/p>\n
It extends the Collection interface, It represents the unordered set and it doesn’t allow us to store the duplicate items. It allows only one null value.<\/p>\n
\n
HashSet <\/strong><\/li>\n
This class implements Set Interface<\/li>\n
HashSet uses a hash table for storage<\/li>\n
Hashing is used to store the elements in the HashSet<\/li>\n
It contains unique items<\/li>\n
LinkedHashSet<\/strong><\/li>\n
LinkedHashSet class represents the LinkedList implementation<\/li>\n
It extends the HashSet class and implements the Set interface<\/li>\n
Like HashSet, It also contains unique elements<\/li>\n
It maintains the insertion order and permits null elements.<\/li>\n<\/ul>\n
SortedSet Interface<\/strong><\/p>\n
SortedSet is the alternate of the Set interface that provides a total ordering on its elements, The elements of the SortedSet are arranged in the increasing order<\/p>\n
\n
TreeSet<\/strong><\/li>\n
TreeSet class implements the Set interface<\/li>\n
Uses a tree for storage<\/li>\n
TreeSet also contains unique elements<\/li>\n
The elements in TreeSet are stored in ascending order<\/li>\n<\/ul>\n
Map Interface<\/strong><\/p>\n
A map contains values based on the key, i.e. key and value pair, It takes the key, and the value pair is known as an entry. A Map is useful if you have to search, update or delete elements based on a key, A Map doesn’t allow duplicate keys but allows duplicate values.<\/p>\n
\n
HashMap<\/b><\/li>\n
HashMap is the implementation of Map<\/li>\n
It <\/strong>doesn’t maintain any order<\/li>\n
LinkedHashMap<\/strong><\/li>\n
LinkedHashMap is the implementation of Map<\/li>\n
It inherits the HashMap class<\/li>\n
It maintains insertion order<\/li>\n
TreeMap<\/strong><\/li>\n
TreeMap is the implementation of Map and SortedMap<\/li>\n
It maintains ascending order.<\/li>\n<\/ul>\n
3. What is the difference between Array List and LinkedList? Which is better explain?<\/a><\/h3>\n
\n
ArrayList<\/strong> Uses Dynamic Array to Store, LinkedList<\/strong> uses a doubly linked list to store elements.<\/li>\n
ArrayList<\/strong> is better for storing and accessing data, LinkedList<\/strong> is better for manipulating data<\/li>\n
The ArrayList<\/strong> class can act as a list only because it implements only List. LinkedList<\/strong> class can act as a list and queue both because it implements both List and Deque interfaces<\/li>\n<\/ul>\n
Which is better ArrayList or LinkedList?<\/strong><\/p>\n
\n
It depends on the purpose we are using,<\/li>\n
ArrayList is good for accessing and sorting<\/li>\n
LinkedList is good for manipulation<\/li>\n
If you remove the element from an array, bit shifting is required at the memory level<\/li>\n
LinkedList is a doubly-linked list so bit shifting is not needed<\/li>\n<\/ul>\n
4. What is the difference between List and Set?<\/a><\/h3>\n
\n
The List<\/strong> is an ordered sequence. The Set<\/strong> is an unordered sequence<\/li>\n
The list<\/strong> allows duplicate elements. Set<\/strong> doesn\u2019t allow duplicate elements<\/li>\n
The list<\/strong> can hold multiple nulls. The set<\/strong> allows only one null<\/li>\n
The list<\/strong> allows access items by index, Set<\/strong> doesn\u2019t allow access by index<\/li>\n
ArrayList, LinkedList, Vector, Stack are an example for List<\/strong> implementation. HashSet, LinkedHashSet, etc. are the implementation of Set.<\/strong><\/li>\n<\/ul>\n5. What is the difference between HashSet and HashMap?<\/a><\/h3>\n
\n
HashSet<\/strong> implements Set interface, HashMap<\/strong> implements Map interface<\/li>\n
HashSet<\/strong> doesn\u2019t allow duplicates. HashMap<\/strong> only duplicate values are allowed, keys are still unique<\/li>\n
A single object can be added to HashSet<\/strong>, For HashMap<\/strong> adding an item requires at least a key-value pair so it will be two objects<\/li>\n
HashSet<\/strong> allows single null value, HashMap<\/strong> allows Single null key and any number of null values.<\/li>\n<\/ul>\n6. Explain Collection and Collections in Java?<\/a><\/h3>\n
\n
The collection<\/strong> is an interface<\/strong>, with the Collection interface we can group various objects into a single unit. Collections<\/strong> is simply a utility class<\/strong> that is found in java.util package<\/li>\n
Collection<\/strong> can be considered as the root for major interfaces like Sets, Lists, Maps, Queue, Deque. Collections<\/strong> provide a method for developers to perform certain basic operations on elements.<\/li>\n
Not all the methods inside Collection<\/strong> is static. Collections<\/strong> has all static method<\/li>\n
Collection<\/strong> is used to store the list of objects in a single object. Collections<\/strong> is used to operate on a collection.<\/li>\n<\/ul>\n7. Explain the difference between Comparable and Comparator.<\/a><\/h3>\n
\n
Comparable<\/strong> provides a single sorting sequence. The Comparator<\/strong> provides multiple sorting sequences<\/li>\n
Comparable<\/strong> allows us to sort the collection on the basis of a single element such as id or name etc. Comparator<\/strong> allows us to sort the collection on the basis of multiple elements such as id and name etc<\/li>\n
The actual class is modified with Comparable<\/strong>. Comparator<\/strong> doesn’t modify the actual class<\/li>\n
Comparable<\/strong> provides compareTo() method to sort elements. Comparator<\/strong> provides compare() method to sort elements.<\/li>\n
Comparable<\/strong> is present in java.lang package. A Comparator<\/strong> is present in java.util package.<\/li>\n
We can sort the list elements of Comparable<\/strong> type by Collections.sort(List) method. We can sort the list elements of Comparator<\/strong> type by Collections.sort(List, Comparator) method.<\/li>\n<\/ul>\n8. Are Array and Array List are the same? If Not, How do we convert them to each other?<\/a><\/h3>\n
Array and ArrayList are not the same. The array is a fixed-length data structure whereas ArrayList is a variable-length Collection class. We cannot change the length of the array once created in Java but ArrayList can be changed.<\/p>\n
<\/strong><\/p>\n
Example Code Snippet : Covert ArrayList into Array<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
import java.util.ArrayList;<\/span><\/p>\n
import java.util.Arrays;<\/span><\/p>\n
\/\/Convert ArrayList into array<\/span><\/p>\n
public class Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String[] args) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ArrayList<String> list = new ArrayList<String>();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 list.add(“One”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 list.add(“Two”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 list.add(“Three”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 list.add(“Four”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Print elements inside List => ” + list.toString());<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Convert to array<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Object[] array = list.toArray();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Print elements inside Array => ” + Arrays.toString(array));<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Iterate through one by one and convert them into string<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 for (Object o : array) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 String s = (String) o;<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(s);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/strong><\/span><\/p>\n
Print elements inside List => [One, Two, Three, Four]<\/span><\/p>\n
Print elements inside Array => [One, Two, Three, Four]<\/span><\/p>\n
One<\/span><\/p>\n
Two<\/span><\/p>\n
Three<\/span><\/p>\n
Four<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
Example Code Snippet : Convert Array to List<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
import java.util.;<\/span><\/p>\n
\/\/Convert array to List<\/span><\/p>\n
class Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String[] args) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 String[] stringArray = { “One”, “Two”, “Three”, “Four” };<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Printing Array = > ” + Arrays.toString(stringArray));<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Convert array to List<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ArrayList<String> list = new ArrayList<String>();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Collections.addAll(list, stringArray);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Printing ArrayList = > ” + list);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/span><\/strong><\/p>\n
Printing Array = > [One, Two, Three, Four]<\/span><\/p>\n
Printing ArrayList = > [One, Two, Three, Four]<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
9. What is Generic Class? Could you explain with a small snippet?<\/a><\/h3>\n
A class that can refer to any type is known as a generic class. That means it has parametrized types. It can allow many types such as String, Integer, or User Defined Types parameter to Class<\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
import<\/span><\/strong>
\njava.util<\/u>.;<\/span><\/p>\n
\/\/Generic Class it accepts any type<\/span><\/p>\n
class<\/strong> GenericClass<T> {<\/span><\/p>\n
\u00a0\u00a0\u00a0 T object;<\/span><\/p>\n
\u00a0\u00a0\u00a0 void<\/strong> add(T object) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 this<\/strong>.object = object;<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 T get() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 return<\/strong>
\nthis<\/strong>.object;<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
class<\/strong> Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 public<\/strong>
\nstatic<\/strong>
\nvoid<\/strong> main(String[] args) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Pass Integer to Generic Class<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 GenericClass<Integer> integerObject = new<\/strong> GenericClass<Integer>();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 integerObject.add(5);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out<\/em><\/strong>.println(“The Added Integer is : ” + integerObject.get());<\/span><\/p>\n
\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0 \/\/ Pass String to Generic Class<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 GenericClass<String> stringObject = new<\/strong> GenericClass<String>();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 stringObject.add(“RahulShetty Academy”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“The Added String is : ” + stringObject.get());<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/strong><\/span><\/p>\n
The Added Integer is : 5<\/span><\/p>\n
The Added String is : RahulShetty Academy<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
10. How Sub Class is different from Inner Class?<\/a><\/h3>\n
\n
Sub class is a class that extends or inherit another class (Inheritance Concept). Inner Class is a class that is nested within another class<\/li>\n
Sub class can be accessed directly. Inner class can only be accessed using reference of outer class. Sub class is accessed directly<\/li>\n<\/ul>\n
Example Code Snippet : Inner Class Demo<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
\/\/Inner class Demo<\/span><\/p>\n
class Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 class InnerClass{<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 void print() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Inside Inner Class”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String[] args) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/Create Object for Outer Class<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Main main = new Main();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \/\/Create Object for Inner Class<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Main.InnerClass inner = main.new InnerClass();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 inner.print();<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/span><\/strong><\/p>\n
Inside Inner Class<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
Example Code Snippet : Sub Class Demo<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
\/\/Sub Class Demo<\/span><\/p>\n
class SuperClass{<\/span><\/p>\n
\u00a0\u00a0\u00a0 void print() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Super Class”);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
class SubClass extends SuperClass {<\/span><\/p>\n
\u00a0\u00a0\u00a0 void print() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Sub Class”);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
public class Main{<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 public static void main(String[] args) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 SubClass sub = new SubClass();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sub.print();<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/strong><\/span><\/p>\n
Sub Class<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
11. What is a singleton class? Explain with a small code snippet<\/a><\/h3>\n
A singleton class is a class that can have only one object (an instance of the class) at any point in time.<\/p>\n
After the first time Creation of an object, if we try to create the object for the Singleton class, the new object also points to the first instance created.<\/p>\n
<\/strong><\/p>\n
Example Code Snippet<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
class SingletonDemo {<\/span><\/p>\n
\u00a0\u00a0\u00a0 private static SingletonDemo single_instance = null;<\/span><\/p>\n
\u00a0\u00a0\u00a0 public int i;<\/span><\/p>\n
\u00a0\u00a0\u00a0 \/\/ Private constrcutor;<\/span><\/p>\n
\u00a0\u00a0\u00a0 private SingletonDemo() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 i = 10;<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 \/\/ Static method to create instance of Singleton class<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static SingletonDemo getInstance() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 if (single_instance == null)<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 single_instance = new SingletonDemo();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 return single_instance;<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
<\/div>\n
\n
\n
class Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String args[]) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 SingletonDemo one = SingletonDemo.getInstance();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 one.i = 50;<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 SingletonDemo two = SingletonDemo.getInstance();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 two.i = 100;<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Print Value of i using object one :” + one.i);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Print Value of i using object two :” + two.i);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 if (one == two) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“one and two both objects are same”);<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
<\/div>\n
\n
\n
Output:<\/span><\/span><\/strong><\/p>\n
Print Value of i using object one :100<\/span><\/p>\n
Print Value of i using object two :100<\/span><\/p>\n
one and two both objects are same<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
12. Explain Thread life cycle briefly? What are some commonly used methods?<\/a><\/h3>\n
Threads are light-weight processes within a process<\/p>\n
Life Cycle of Thread<\/p>\n
The thread can be in one of the states at a given point in time<\/p>\n
NEW<\/strong>: A thread that has not yet started is in this state.<\/p>\n
RUNNABLE<\/strong>: A thread executing in the Java virtual machine is in this state.<\/p>\n
BLOCKED<\/strong>: A thread that is blocked waiting for a monitor lock is in this state.<\/p>\n
WAITING<\/strong>: A thread that is waiting indefinitely for another thread to perform a particular action is in this state.<\/p>\n
TIMED_WAITING<\/strong>: A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.<\/p>\n
TERMINATED<\/strong>: A thread that has exited is in this state.<\/p>\n
Commonly Used Methods in Java Thread.<\/strong><\/p>\n
start():<\/strong> Starts the thread.<\/p>\n
getState(): <\/strong>It returns the state of the thread.<\/p>\n
getName():<\/strong> It returns the name of the thread.<\/p>\n
getPriority():<\/strong> It returns the priority of the thread.<\/p>\n
sleep():<\/strong> Stops the thread for the specified time.<\/p>\n
Join():<\/strong> Stops the current thread until the called thread gets terminated.<\/p>\n
isAlive() :<\/strong> Checks if the thread is alive.<\/p>\n
Example Code Snippet: Simplest possible Thread example in Java<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
class Main extends Thread{<\/span><\/p>\n
\u00a0public void run() {<\/span><\/p>\n
\u00a0\u00a0\u00a0 \u00a0System.out.println(“Thread is running”);<\/span><\/p>\n
\u00a0}<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String args[]) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 new Main().start();<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/strong><\/span><\/p>\n
Thread is running<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
13. What is garbage collection? How to force Garbage Collection?<\/a><\/h3>\n
Garbage collection is the process by which Java programs perform automatic memory management. The garbage collector finds these unused objects and deletes them to free up memory.<\/p>\n
How to force Garbage Collection?<\/strong><\/p>\n
Using System.gc()<\/strong><\/p>\n
If you call System.gc() anywhere in their code to instruct the JVM to prioritize garbage collection<\/p>\n
Using Runtime.getRuntime().gc()<\/strong><\/p>\n
Internally it calls System.gc(), however, this method can also be used for forcing the garbage collection in java<\/p>\n
Note: When an object is set to null, Java automatically prioritizes that to eligible for \u00a0Garbage Collection<\/em><\/p>\n
Example Code Snippet : System.gc() and Runtime.getRuntime().gc()<\/strong><\/p>\n<\/div>\n
\n
<\/div>\n
\n
\n
class Main {<\/span><\/p>\n
\u00a0\u00a0\u00a0 public void finalize() {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.out.println(“Object is Garbage Collected\u00a0 ” + this);<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
\u00a0\u00a0\u00a0 public static void main(String args[]) {<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Main m1 = new Main();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Main m2 = new Main();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 m1 = null;<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 System.gc();<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 m2=null;<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Runtime.getRuntime().gc();<\/span><\/p>\n
\u00a0\u00a0\u00a0 }<\/span><\/p>\n
}<\/span><\/p>\n
Output:<\/span><\/strong><\/span><\/p>\n
Object is Garbage Collected\u00a0 Main@17f18626<\/span><\/p>\n
Object is Garbage Collected \u00a0Main@19366aa8<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n
Course Alert
<\/span><\/em><\/h5>\n
If you are interested in landing a SDET or Sr. QA Automation Engineer role, check out our popular SDET course to learn the fundamental skills required an SDET needs to perform at work. Also, I have another popular course which covers Top 150+ Interview questions most commonly asked in SDET \/ Automation interviews.<\/strong><\/p>\n<\/div>\n
\n
\n
\n
\n
SDET\/Test Architect Essentials -Road to Full stack QA<\/a><\/span><\/li>\n
\n
\n
SDET\/QA Automation Interview Kit + Java logic Programs<\/a><\/span><\/li>\n<\/ul>\n<\/div>\n
\n
\n
<\/div>\n
\n
\n
A Quick Note<\/strong><\/em><\/h4>\n<\/div>\n\n
Please remember all these courses comes with 100% Lifetime acces<\/strong>s<\/strong> and free updates for Lifetime!!<\/strong><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n
Please click on the link\u00a0Sr.QA and SDET Interview Questions in Java \u2013 Part 4<\/span><\/a><\/strong> to continue to part-4 series of this article.<\/p>\n<\/div>\n<\/div>\n<\/div>\n
<\/div>\n<\/section>\n
<\/body><\/html><\/p>\n","protected":false},"excerpt":{"rendered":"
table of contents 1. How can we achieve Pass by value and pass by reference in Java? 2. Explain Different types of interfaces in the Collection framework 3. What is the difference between Array List and LinkedList? Which is better explain? 4. What is the difference between List and Set? 5. What is the difference […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,5],"tags":[],"class_list":["post-1229","post","type-post","status-publish","format-standard","hentry","category-interview-questions","category-java","post-wrapper","thrv_wrapper"],"_links":{"self":[{"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/1229","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=1229"}],"version-history":[{"count":0,"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/1229\/revisions"}],"wp:attachment":[{"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=1229"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=1229"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rahulshettyacademy.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=1229"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}