- Explain lamda expression and functional expressions ?
- Why we are using functional annotation for functional interface
- If catch is not present, only finally is present, will the code work ?
- multiple catch with single finally will work ?
- What is transient in serialization ?
- Can we serialize static variables ?
- What happens if your Serializable class contains a member which is not serializable? How do you fix it ?
https://www.youtube.com/shorts/IpwvQlyyEDY
-
https://medium.com/devops-dev/java-collection-list-arraylist-interview-q-a-04dbaf197192
- Can you iterate and remove the element of ArrayList at the same time ?
- Can you tell me how hashmap internally works ?
- What is concurrent hashmap ?
- What is weak hashmap ?
- How load factor works in hashmap ?
- Difference between Hashmap vs Hashtable ?
- What will happen if we put key object in hashmap which is already there ?
- Difference between Stack and Queue ?
- What is Hashtable ?
- How blocking queue works ?
- Difference between hashmap and concurrent Hashmap ?
- Lets say you are working with hashmap, First key is null, value is Ravi, Second key is null, value is Bisht, hashmap.get(null), what will I get
- What is synchronization ?
- What are the core interfaces of Hibernate?
- What is lazy loading in hibernate?
- What are the states of the object in hibernate?
- What is the difference between session.save() and session.persist() method?
- What is the difference between get and load method?
- What are the different bean scopes in spring?
- Diff between constructor and setter injection ?
- Transaction Management in Spring Boot
- @Transactional Annotation
- How we can read the property from property file ?
- What is use of @Value annotation ?
- Difference between @PathVariable and @RequestParam In Spring Boot
- Difference between @RestController and @Controller In Spring Boot
- What is use of actuators ?
- Singleton Design Pattern
- How to create thread-safe singleton class in java using double checked locking ?
- How do you break a singleton pattern ?
- How do prevent a singleton pattern from breaking ?
- Factory Design Pattern
- Can you override static method in java ?
- Why java does not support operator overloading ?
- Why multiple inheritance is not supported in java ?
- How to create immutable class in java ?
- what was log4j vulnerability?, how to fix log4j vulnerability ?
1. Transaction Management in Spring Boot
- Transaction is a sequence of actions performed by the application that together pipelined to perform a single operation.
https://www.youtube.com/watch?v=6gc-xW4SVa4
### Why char array is preferred to store password than string in java ?
- In Java, using a char[] array to store passwords is preferred over String for several reasons:
1. Mutability: String is immutable, meaning once it's created, it cannot be changed. This can lead to sensitive data like passwords remaining in memory longer than necessary, increasing the risk of exposure.
2. Explicit Clearing: With a char[], you can explicitly overwrite the array (e.g., by setting all elements to zero) after use, which helps minimize the time the sensitive data is in memory.
3. Memory Visibility: Strings are stored in the String pool, making them more likely to be visible in memory dumps or garbage collection logs. char[] does not have this issue.
4. Garbage Collection: Since String objects remain until they are garbage collected, passwords may stay in memory longer, while char[] can be cleared promptly.
- These factors contribute to using char[] for better security and control over sensitive information like passwords.
List<String> strings = Arrays.asList("Hello", "World", "Java", "is", "awesome");
public class ConcatenatingAllString {
public static void main(String[] args) {
List<String> strings = Arrays.asList("Hello", "World", "Java", "is", "awesome");
/* Using StringBuilder: This is the most efficient method for concatenating strings in a loop
* because it avoids the creation of many temporary String objects.
*/
StringBuilder sb = new StringBuilder();
for(String s :strings) {
sb.append(s);
}
String result = sb.toString();
System.out.println(result);
}
}/*Using Collectors.joining: If you are using Java 8 or later,
* you can use the Collectors.joining method with streams to concatenate strings.
- Collectors.joining() joins the characters back into a single string.
*/
public class ConcatenatingAllString {
public static void main(String[] args) {
List<String> strings = Arrays.asList("Hello", "World", "Java", "is", "awesome");
String result = strings.stream().collect(Collectors.joining());
System.out.println(result);
}
}// Lazy Initialization Using double check locking
public class SingletonClass {
private static volatile SingletonClass instance = null;
private SingletonClass() {
}
// Double Checked Locking Pattern
public static SingletonClass getInstance() {
if(instance == null) {
synchronized (SingletonClass.class) {
if(instance == null) {
instance = new SingletonClass();
}
}
}
return instance;
}
}In Java, Multiple Inheritance is not supported
through Class but it is possible by Interface, why?
• As we have explained in the inheritance chapter, in multiple
inheritance, subclasses are derived from multiple superclasses.
• If two superclasses have the same method name then which method
is inherited into subclass is the main confusion in multiple
inheritance.
• That’s why Java does not support multiple inheritance in case of class.
But, it is supported through an interface because there is no
confusion. This is because its implementation is provided by the
implementation class.
10. Write a program to reverse a string ?
18. Write a program to remove duplicates from any array ?
46. Lets say you have two variable a and b, with values 5 and 10. Interchange value of a and b without using a temporary variable ? Will the program work for negative numbers ?
- forEach()
list.stream().forEach(System.out::println);
- collect()
List<String> result = list.stream().collect(Collectors.toList());
- reduce()
Optional<Integer> sum = list.stream().reduce(Integer::sum);
29. What are the other features of Java 8 you have used while coding ?
- In Java, directly removing elements from an ArrayList while iterating over it using a simple for loop or an enhanced for-each loop will result in a ConcurrentModificationException.
- However, you can safely remove elements using an iterator.
import java.util.ArrayList;
import java.util.Iterator;
public class Main {
public static void main(String[] args) {
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
numbers.add(4);
numbers.add(5);
Iterator<Integer> iterator = numbers.iterator();
while (iterator.hasNext()) {
Integer number = iterator.next();
if (number % 2 == 0) { // Example condition: remove even numbers
iterator.remove();
}
}
System.out.println(numbers); // Output: [1, 3, 5]
}
}- Call the remove() method of the Iterator to remove the current element. This method is safe to call during iteration and does not cause a ConcurrentModificationException.
- Using an Iterator is the recommended way to remove elements from a collection while iterating over it.
- The Iterator's remove method ensures that the underlying collection is modified in a way that does not interfere with the iteration process.
49. If insert can happen by PUT why do we have POST
50. can we fetch data with the help of POST ?
51. What is functional interface in java ?
52. Explain some of the functional interfaces which are used in java ?
53. How to make class threadsafe ?
54. What is Eureka Server
55. How do u create custom exceptions ?
56. When will you get 415 & 504 http response code ?
57. Email field has not null contrainst, how to remove not null constraint from not null column
58. What is difference between new Arraylist and Arrays.asList
59. Which one is fast LinkedList or Arraylist ?
60. Which case would you prefer LinkedList and which case Arraylist ?
61. Difference between Aggregation and composition
62. What is Fault tolerance
63. Jwt authentication related questions
64. Heap Memory and JVM
65. How do you create HTTP POST request in Java
66. What is the use of super keyword
67. What is throw, throws and when do we use these ?
69. What is a treeset ?
70. Explain the role of API Gateway in a microservices architecture ?
71. Explain functional interface and what are some of the available interface ?
72. What are REST API Best practices ?
73. What is an one to one mapping and how to set up it with JPA/Hibernate ?
74. Difference between entity object and value object ?
75. What is the difference between ClassNotFoundException and NoClassDefFoundError
76. is finally block always be executed
77. What is an exception in java and how you handle exception in java ?
78. Explain classloader in java ?
80. What is immutable classes & how we can create a new immutable class ?
81. Difference between comparator and comparable in java ?
82. What is hash collision ?
83. How will you handle Null pointer exception ?
86. What is volatile keyword ?
87. What are design patterns you have worked on ?
88. How to create a singleton class ?
89. What is garbage collection ?
90. There is a method called GC, what is the purpose ?
91. How garbage collection works internally in java ?
96. What is CI and CD, and why it is important ?
97. Why the main method is static in java ?
98. Can we override private variable in java ?
99. What is blank final variable in java, If we declare a final variable but we havenot assigned any value, what happens here ?
100. How the java objects are stored in memory ?
101. List of mobile numbers, find customers having number +91 ?
102. What is Predicate in terms of functional interface ?
103. Explain builder design pattern ?
104. How security is managed by your application ?
105. Do you know what is JWT2.0 and JWT token ?
106. Advantages of hibernate over JDBC ?
107. What is session in hibernate and is it thread safe ?
108. What is lazy loading in hibernate ?
109. can you override private and static method ?
110. What happens if an exception is thrown by Super class ?
111. What is wrapper class ?
112. What is garbage collection ?
113. Write a singleton design pattern in multi threaded environment ?
114. You need to store password .What type of datatype you will use?
115. What is the difference between factory and abstract factory design pattern ?
116. Difference between sleep() and wait();
117. Can you access non static variable in static contest ?
118. Suppose you declare variables outside main method . how to access variables in main method?
119. What is the difference between Comparator and Comparable in java
120. Is it better to make method synchronized or critical section synchronized?
121. in try catch and finally we return the value, priority is in which block ?
122. What is a Aggregation ?
123. Have you used Hibernate. What is the difference between hibernate first level cache and second level cache.
124. What is Inversion Of Control ?
125. How garbage collection works in java ?
126. Which scenario have you used Optional class & how optional class is really helpful ?
127. Which scenario we will use arraylist and when we will use linked list ?
128. Do you know what is Singleton ?
129. what are objectives of get put post and delete methods ?
130. API, Can we use get method to create resourses ?
131. Employee Service class will be annotated with which annotation ?
132. What would happen if I dont import java.lang method ?
133. Have you used serialization anywhere in your application ?
134. What is response entity and benefit of using response entity ?
135. What is docker and docker image and docker container ?
136. Suppose I have list and I want to reverse it, how can i do that ?
137. Can you tell me real world example of encapsulation ?
138. What is stateless object ?
139. Can you tell me difference @ Component @ Service and @ Repository annotation ?
140. Reason of overriding equals and hashcode method ?
141. Have you used reflections anywhere ?
142. How can we create object dynamically at runtime in java ?
143. Is it possible to rethrow an exception ?
144. Hashset vs TreeSet, which one is better in which scenario ?
145. What is use of Generics in java ?
146. What is use of CopyonWrite Arraylist ?
147. Synchronized block or method as synchronized, which one is better ?
148. What type of IDE you are using ?
149. Can you tell me the difference between truncate and delete ?
150. What are the different types of exceptions you have faced till now
151. What is order of exception in java, which is highest
152. Where will be a new object stored- heap or stack?
153. What is instance level locking and class level locking ?
154. Difference betwen normal interface and functional interface ?
155. There is primitive data type int and wrapper class Integer. Which will take more memory ?
156. I am expecting an exception in one of my code, how can i write test case for that ?
157. Difference between unit test and integration test ?
158. What is test driven development and what do you think about it ?
159. Database ACID properties
160. What are joins in database ?
161. In database, when we use union, intersection. suppose same thing we want to apply in JPA ?
162. How are you saving data into the database
163. Prepared Statements vs Statement in JDBC
164. SQL queries with group by
165. Primary Key Vs Unique Key in database ?
166. What are triggers in database ?
- https://www.youtube.com/watch?v=QgTI3DoVwzE&t=343s
167. SQL query to fetch the name of employee who earn the highest salary ?
168. There is a table called employee in the database, id fn ln , there are few employee records. Now I decided to remove a column phone number. How can i delete it from the table?
169. What is callable interface in threads ?
170. In threads there is a sleep method and there is a wait method, what is the difference ?
171. I want to suspend a thread for a time of 5 seconds, how to do this ?
172. In thread there is shutdown hook, do you know what it is ?
173. How can you make a piece of code thread safe ?
174. How can you take a thread dump in java
175. What is difference between thread and process ?
176. What is @Autowire ?
177. What are spring boot components ?
178. Why spring boot was introduced ?
179. Advantages of using spring boot applications ?
180. How auto configuration works in spring boot ?
181. Do you know why we use @qualifier annotation ?
182. What is bean wiring in spring ?
183. How can I create a spring rest application from scratch ?
184. Which scnearios we will use @component vs @bean in spring boot
185. What @SpringBootApplication will do ?
186. What are spring profiles ?
187. What is actuator in spring boot ?
188. Do you know how to develop an api in spring
189. Explain the purpose of Autowired Annotation in spring ?
190. Main difference between spring and spring boot ?
191. What are scopes of spring bean ?
192. Difference between SpringBoot and Spring Framework ?
193. What is Spring AOP
194. Give examples of commonly used spring boot starters ?
195. @Controller vs @RestController in Spring
196. How a Spring boot application bootstraps ?
197. Which methods are there in comparable ?
198. Difference between compile time and run time exception ?
199. What is static initializer block ?
200. Where the static blocks gets stored inside memory ?
201. What is Externalization in java ?
202. What is use of generics in java ?
203. How to disable a specific auto-configuration class ?
204. What are actuator-provided endpoints used for monitoring the spring boot application ?
205. Can we create a custom annotation ?
206. When we extend the thread class what all method we override and where thread starts ? What is the case when they implement runnable ? any difference ? Can we call start method 2 times
207. What is exception order in catch block ?
208. What all collections have you used in your project ?
209. What is equals and hashcode contract ?
210. Do you know hierarchy in exceptions ?
211. What is classpath ?
212. Difference between jdk, jre and jvm ?
213. How does jvmcontributes to java’s platform independence ?
214. Describe the role of RestController and RequestMapping annotation in spring ?
215. How does spring data JPA work with hibernate for ORM ?
216. In springboot application how would you optimize the data access ?
217. Why spring buffer is called mutable ?
218. Lets say you have developed a rest api, REST api is not able to get that particular resource. What will you return to the client ?
219. What is use of an interface
220. Difference between static and non-static method ?
221. Difference between array and arraylist ?
... will add more real interview questions, check weekly ...
...
Visit my website for focussed learning
https://www.myjavainterview.in/core-java
1. What are conditional annotations in spring boot ?
2. What is the default server provided by spring boot ?
3. How does spring boot support the development of restful web services ?
4. Explain role of EnableAutoConfiguration in spring boot app and how does spring achive auto configuration internally ?
5. Are you aware of actuator endpoints?
- https://www.youtube.com/watch?v=lMDZ6dple9Q
6. What is dependency name for actuator ?
7. Can we secure these actuator endpoints ? and how can we secure it ?
8. Wht strategies would be used to optimize the performance of spring boot applications ?
9. What is Aspect Oriented Programming ?
10. Can you give a usecase of AOP ?
11. Can you explain how spring boot profile ?
12. Which file do you use yml or properties in your current project ?
13. Do we have any benefit of using yml over properties file ?
14. Can you explain component scan and how would you prevent a specific package from being scanned ?
15. Can you explain what is default embedded server provided by the spring boot ?
16. Can we change default embedded server ?
17. How does AOP differs from the traditional programming models ?
18. How to create global exception handler in spring boot application ?
19. How will you call a restful web service from a spring boot application ?
- What is application context and bean factory in spring boot ?
- BeanFactory is the basic container whereas ApplicationContext is the advanced container.
- ApplicationContext extends the BeanFactory interface.
- ApplicationContext provides more facilities than BeanFactory such as integration with spring AOP, message resource handling for i18n etc.
21. What is inversion of control(IOC) or dependency Injection(DI) ?
22. Do you know different types of injections ?
23. How do you handle transactions in spring boot application ?
24. Why we should use spring boot ?
25. What annotations you have used in your spring boot application ?
26. PostMapping vs PutMapping ?
— check weekly,,, will add more
getClass()
int hashCode()
wait()
notify()
notifyAll()
String toString()
- Returns a string representation of the object.
- It is recommended that all subclasses override this method.
clone()
equals()
finalize()
- for Every object jvm will generate a unique number which is nothing but hashCode.
- JVM using hashCode while saving objects into hashing related data structures like HashSet, HashMap, and HashTable etc.
- Using new Keyword
- Using clone() method
- Using Deserialization
- Using newInstance() method of the Class class
- Using newInstance() method of the Constructor class
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "employees")
public class Employee{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private long id; //bigint
private String name; //varchar(255)
// Specifies that the property or field is not persistent.
//It is used to annotate a property or field of an entity class, mapped superclass, or embeddable class.
@Transient
private String gender;
}-
The @Component annotation indicates that an annotated class is a "Spring Bean/Component".
-
The @Component annotattion tells Spring container to automatically create Spring bean.
-
responsibility of creating bean is given to springboot
-
It is a class-level annotation.
-
It is used to mark a Java class as a bean.
-
A Java class annotated with @Component is found during the classpath .
-
The Spring Framework pick it up and configure it in the application context as a Spring Bean.
- Cloning in Java
https://www.youtube.com/watch?v=e1Mw-vNXuFY
Filter and Find Even Number using java 8
Find Sum of Squares using java 8
Sort a list of string using java 8
Double Each Number of List using java 8
Find distinct element from the list using java 8
https://www.youtube.com/watch?v=BESfZAZnABs&t=3s
public class MapExample {
public static void main(String[] args) {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("ABHAY KASHINATH PATIL", 416404);
map.put("ANUP SANJAY DHOTRE", 457030);
map.put("ADV NAJIB SHAIKH", 3300);
map.put("NOTA", 5783);
map.put("AMBEDKAR PRAKASH YASHWANT", 276747);
for(Map.Entry<String,Integer> m:map.entrySet()) {
System.out.println(m.getKey()+" " + m.getValue());
}
//How to sort a Map based on keys or values using stream
TreeMap<String, Integer> tm = new TreeMap<String, Integer>(map);
System.out.println(tm);
//Sort By Key
map.entrySet().stream().sorted(Map.Entry.comparingByKey()).forEach(e -> System.out.println(e));
//Sort By Value
map.entrySet().stream().sorted(Map.Entry.comparingByValue()).forEach(e -> System.out.println(e));
}
}- Java8 Streams Interview Question-26-How to sort a Map based on keys or values using stream?-by Naren
https://www.youtube.com/watch?v=Mf7hSRZsHFs
-Method overloading in depth
https://www.youtube.com/watch?v=e1QJKOGLwj4
Find Even Number Using java 8.
Find Sum of Squares Using Java 8.
Sort a List Of String Using Java 8.
Double Each Number Of The List Using Java 8.
Find distinct eleement from the list Using Java 8.
Group by Strings of equal length from the List using Java 8.
Remove String elements from List where String contains "an" using Java 8.
Join each element from the list of string to form one comma separated String
https://www.youtube.com/watch?v=BESfZAZnABs
https://www.youtube.com/watch?v=-ORgK_JkOa4&list=PLFGoYjJG_fqp52WKlmgF4cV72KS9_9tih
Hibernate Mapping
OneToOne
1.User and Cart
2.Customer and Shipping address
- Each Customer has one shipping address.
- Hibernate uses a shared primary key to link them.
OneToMany
1.Order and OrderItems
2.Product and Reviews
- a product can have multiple reviews.
- Hibernate uses a foreign key in the review table.
ManyToMany
1.Product and Category
2.Customer and Product
-Each Customer can purchase multiple Products.
-Products can be purchased by multiple customers.
What are the different bean scopes in spring?
1.Singleton
2.Prototype
3.Request
4.Session
5.Application
6.WebSocket
How to find second highest salary in SQL
1.max
select max(salary) from employee where salary < (select max(salary) from employee)
2. limit
3. top
https://www.youtube.com/watch?v=a3ngELoA9h0
- If you declare a class abstract, to use it, you must extend it and if you declare a class final you can not extend it,
- since both contradict with each other you can not declare a class both abstract and final if you do so a compile time error will be generated.
- A real-time example of a final class in Java is the java.lang.String class,
- which is a final class and cannot be extended by any other class.
- This is because the String class is complete in nature and cannot be modified
- Immutable String or Object that can not be modified once it is created. But We can only change the reference to the object.
- The String is immutable in java because of the security,synchronization and concurrency ,caching and class loading.
- String Constant Pool provides the facility of reusability of the existing string object.
- When a new string object is created using the string literals ,then JVM first checks in the pool if this string already exists or not. if it exists ,then it will reference the existing string rather than creating a new object.
- this will help in the speeding up of the application and also helps in saving the memory as no two objects will have the same content.
public - this method is accessible from outside the class.
static - No object is required to call the main method.
void - this method does not return any value.
main - Special method name to start the java program execution.
String[] args - the arguments passed while running the program.
- Yes can change the order of public and static keywords , but void should come just before the method name.
- Garbage collection
- Java provides automatic memory management through a program called Garbage collector.
- "Remove objects that are not used anymore."
- live object = reacheable (referenced by someone else)
- dead object = unreachable (not referenced from anywhere)
- Garbage collection is carried out by a daemon thread called "Garbage collector"
- we can not force gc to happen (System.gc())
- We cannot create an object of abstract class but we can create an object of subclass of abstract class.
- When we create an object of subclass of an abstract class, it calls the constructor of subclass.
- This subclass constructor has super in the first line that calls constructor of an abstract class.
- Thus, the constructors of an abstract class are used from constructor of its subclass.
- If the abstract class doesn’t have a constructor, a class that extends that abstract class will not get compiled.
java -jar yourfile.jar
mvn package
mvn clean package
This command will compile the source code, run tests, and package the project into the specified format (usually a JAR file).
- One is by extending java.lang.Thread class
- Another is by implementing java.lang.Runnable interface
because Runnable is interface and it has abstract method called run.
Hence when we implement the Runnable interface we have to override run() method.
- No. You can not start thread twice
- This will result in a IllegalThreadStateException
public class StartTwice{
public static void main(String[] args){
Thread t = new Thread();
t.start();
t.start();
}
}- Thread use wait(), notify(), and notifyAll() to communicate with each other.
- Yes, But recommendadation is to follow guidlines
- if you are requirement is to create resource then go for POST
- if you are requirement is to Update resource then go for PUT PATCH
https://www.youtube.com/watch?v=drwOMR3O0zc
- Serialization is a mechanism of converting the state of an object into a byte stream.
- Deserialization is the reverse process where the byte stream is used to recreate the actual Java object in memory.
Note: The byte stream created is platform independent. So, the object serialized on one platform can be deserialized on a different platform.
- To transfer objects through a network.
- To keep Java objects in memory.
- To save Java objects in files.
- For serializing the object, we call the writeObject() method of ObjectOutputStream, and for deserialization we call the readObject() method of ObjectInputStream class.
- We must implement the Serializable interface for serializing the object.
- every serializable class/object gets associated with a unique identification number provided by the JVM of the host machine.This Unique ID is called Serial Version UID.
- This UID is used as an identification by the JVM of the receiving end to confirm that the same object is being DeSerialized at the receiving end.
- Transient Keyword is a reserved keyword in Java.
- It is used as a variable modifier at the time of the Serialization process.
- Declaring a variable with Transient keyword avoids the variable from being Serialized.
- During deserialization, the transient variable will be assigned a default value, typically null for reference types or 0 for primitive types.
public class MaxAndMinElementArray {
public static void main(String[] args) {
int a[]={1,423,6,46,34,23,13,53,4};
int max = a[0];
for(int i = 1;i<a.length;i++) {
if(a[i] > max) {
max = a[i];
}
}
System.out.println(Arrays.toString(a));
System.out.println("Maximum Element is : " + max);
int min = a[0];
for(int i=1 ;i < a.length ; i++) {
if(a[i] < min) {
min = a[i];
}
}
System.out.println("Minimum Element is : " + min);
}
}public class ReverseArray {
public static void main(String[] args) {
int [] arr = {1,3,5,7,4,8,9};
System.out.println("before Reverse : "+ Arrays.toString(arr));
reverseArray(arr);
System.out.println("after Reverse : "+ Arrays.toString(arr));
}
private static void reverseArray(int[] arr) {
int i = 0;
int j = arr.length-1;
while(i<j) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
i++;
j--;
}
}
}public class SubArray {
public static void subArray(int arr[]) {
int len = arr.length;
for (int i = 0; i < len; i++) {
for (int j = i; j < len; j++) {
for (int k = i; k <= j; k++) {
System.out.print(arr[k] + " ");
}
System.out.println();
}
}
}
public static void main(String[] args) {
int arr[] = { 1, 2, 3, 4, 5 };
subArray(arr);
}
}Output :
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
2
2 3
2 3 4
2 3 4 5
3
3 4
3 4 5
4
4 5
5
public class MergeSortedArray {
public static void main(String[] args) {
int[] arr1 = {1,2,3,5,7};
int[] arr2 = {3,5,7,9};
int [] result = mergeSorted(arr1,arr2);
System.out.println(Arrays.toString(result));
}
private static int[] mergeSorted(int[] arr1, int[] arr2) {
int len1 = arr1.length;
int len2 = arr2.length;
int [] result = new int[len1+len2];
int i=0,j=0,k=0;
while(i< len1 && j< len2) {
if(arr1[i]<arr2[j]) {
result[k] = arr1[i];
i++;
k++;
}else {
result[k] = arr2[j];
j++;
k++;
}
}
while(i<len1) {
result[k++]=arr1[i++];
}
while(j<len2) {
result[k++]=arr2[j++];
}
return result;
}
}public class MissingNumberInArray {
public static void main(String[] args) {
// Array should not have duplicates
// Array No need be Sorted order
int [] arr = {1,2,3,5};
// 1+2+3+5=11
int sum1 = 0;
for(int i = 0 ; i< arr.length; i++) {
sum1 = sum1 + arr[i];
}
System.out.println("Sum of Elements in Array ="+sum1);
// 1+2+3+4+5 = 15
int sum2=0;
for(int i =1;i<=5;i++) {
sum2 = sum2 +i;
}
System.out.println("Sum Of Range Of Elements in Array ="+sum2);
System.out.println("Missing Number is = "+(sum2-sum1));
}
}- input = {4,2,3,2,1,3,4,5};
public class DuplicateElementArray {
public static void duplicateElement(int [] arr) {
int len = arr.length;
for(int i=0; i<len; i++) {
for(int j = i+1; j<len; j++) {
if(arr[i]==arr[j]) {
System.out.println(arr[i]);
}
}
}
}
public static void main(String[] args) {
int [] input = {4,2,3,2,3,1,3,4,5};
duplicateElement(input);
}
}- Use Collections.unmodifiableList() method.
public class ReadOnlyArrayList {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("Apple");
list.add("Banana");
list.add("Mango");
System.out.println(list);
List<String> readOnlyList = Collections.unmodifiableList(list);
readOnlyList.add("Kiwi"); //UnsupportedOperationException
}
}public class AverageSalaryByDepartment {
public static void main(String[] args) {
List<Employee> employees = Arrays.asList(
new Employee("John", "HR", 50000),
new Employee("Jane", "IT", 60000),
new Employee("Doe", "IT", 70000),
new Employee("Smith", "HR", 55000),
new Employee("Alice", "Finance", 75000),
new Employee("Bob", "Finance", 80000)
);
Map<String, Double> averageSalaryByDepartment = employees.stream()
.collect(Collectors.groupingBy(Employee::getDepartment,
Collectors.averagingDouble(Employee::getSalary)));
System.out.println("Average Salary by Department:");
averageSalaryByDepartment.forEach((department, averageSalary) ->
System.out.println(department + ": " + averageSalary));
}
}public class Main {
public static void main(String[] args) {
List<Employee> employees = new ArrayList<>();
employees.add(new Employee("John", 30, 50000));
employees.add(new Employee("Alice", 25, 60000));
employees.add(new Employee("Bob", 35, 45000));
// Sorting employees by name
List<Employee> sortedByName = employees.stream()
.sorted(Comparator.comparing(Employee::getName))
.toList();
System.out.println("Employees sorted by name:");
sortedByName.forEach(System.out::println);
// Sorting employees by age
List<Employee> sortedByAge = employees.stream()
.sorted(Comparator.comparingInt(Employee::getAge))
.toList();
System.out.println("\nEmployees sorted by age:");
sortedByAge.forEach(System.out::println);
// Sorting employees by salary
List<Employee> sortedBySalary = employees.stream()
.sorted(Comparator.comparingDouble(Employee::getSalary))
.toList();
System.out.println("\nEmployees sorted by salary:");
sortedBySalary.forEach(System.out::println);
}
}https://www.youtube.com/watch?v=I8r858beW0o
https://www.youtube.com/watch?v=lMDZ6dple9Q
https://www.youtube.com/watch?v=awV2rVy-i_8
https://javatechonline.com/java-stream-api-interview-questions/
https://javatechonline.com/java-8-coding-interview-questions-java/
https://www.youtube.com/playlist?list=PLUDwpEzHYYLvWEwDxZViN1shP-pGyZdtT
https://www.youtube.com/watch?v=emhAf7srIeg
- Exception is a unwanted event which disturbs the normal flow of execution.
- exception is an abnormal condition that occurs during the execution of program to stop the entire flow of application.
public class ConvertListToArray {
public static void main(String[] args) {
List<String> al = new ArrayList<String>();
al.add("A");
al.add("B");
al.add("C");
al.add("D");
al.add("E");
System.out.println(al);
// Approach 1
String[] strArray = new String[al.size()];
al.toArray(strArray);
System.out.println(Arrays.toString(strArray));
// Approach 2
String[] array = al.stream().toArray(String[] :: new);
System.out.println(Arrays.toString(array));
}
}