Interview Questions and Answers for 'Java' | Search Interview Question

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Q11. What are the different ways of creating threads in java?

Ans. There are two ways to create the threads in java
a) By extending java.lang.Thread class.
b) By implementing java.lang.Runnable interface.

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Q12. What are Loops in Java? What are three types of loops?

Core Java

Ans. Looping is used in programming to execute a statement or a block of statement repeatedly. There are three types of loops in Java:
1) For Loops
For loops are used in java to execute statements repeatedly for a given number of times. For loops are used when number of times to execute the statements is known to programmer.
2) While Loops
While loop is used when certain statements need to be executed repeatedly until a condition is fulfilled. In while loops, condition is checked first before execution of statements.
3) Do While Loops
Do While Loop is same as While loop with only difference that condition is checked after execution of block of statements. Hence in case of do while loop, statements are executed at least once.

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Q13. What is the difference between double and float variables in Java?

Core Java

Ans. In java, float takes 4 bytes in memory while Double takes 8 bytes in memory. Float is single precision floating point decimal number while Double is double precision decimal number.

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Q14. Can main() method in Java can return any data?

Core Java

Ans. In java, main() method can't return any data and hence, it's always declared with a void return type.

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Q15. What's the difference between an array and Vector?

Core Java

Ans. An array groups data of same primitive type and is static in nature while vectors are dynamic in nature and can hold data of different data types.

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Q16. How to swap two numbers without using a third variable?

Core Java

Ans. int a = 10;
int b = 20;

b = b + a; // now b is sum of both the numbers
a = b - a; // b - a = (b + a) - a = b (a is swapped)
b = b - a; // (b + a) - b = a (b is swapped)

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Q17. Explain method overridding.

Core Java

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Q18. Write a program to print next largest palindrome number?

Core Java

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Q19. What are the benefits of using UI framework like Angular , View js etc instead of plain vanilla js and html ?

Javascript

Ans. These frameworks facilitates easier product development and enhancement and maintainability by having separation of concerns ( using oops ) and helps in development of reusable libraries / components. So in nutshell , they make development and maintenance of large scale application easier.

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Q20. Have you ever used sessionStorage ? What is the better way to store session information - sessionStorage or session cookie ?

Session Management

Ans. Session Cookie, because session storage can be accessed from XSS (Cross site Scripting) attacks but cookies (if set with "HttpOnly" and "Secure" flags) are more safer against these attacks.

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Q21. String processing in Java

Core Java

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Q22. what is strict mode in javascript ? How is it used ?

Javascript

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Q23. What is concurrent interface ?

Core Java

Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package.

HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5.

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Q24. What are the benefits of Java over other Programming Languages ?

Core Java

Ans. 1. JVM that makes it platform independent and facilitates portability.
2. Garbage Collector that protects from Memory Leaks.
3. Only usage of references and not pointer arithmetic and hence protects the application from memory issues like dangling pointers, memory leaks etc.
4. Support for OOPs that makes application development and maintenance easy.
5. Facilitates library development through use of interface / abstract classes.
6. Facilitates creation of scalable applications.
7. Huge repository of libraries and pool of people with java skill.

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Q25. What is the different between collection and Stream Api ?

Core Java

Ans. data under collection are actually stored in memory so that they can be retrieved when needed whereas data in streams are not stored and hence we need to construct it again when needed.

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Q26. How is cohesion achieved in JavaScript ?

JavaScript

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Q27. How Object-Oriented Programming is implemented in JavaScript? How they differ from other languages?

Javascript

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Q28. Explain Servlet config

Java EE

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Q29. Interface vs Abstraction

Core Java

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Q30. How is the declaration of enum in Typescript differ from Javascript ?

TypeScript

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Q31. What are benefits of strongly typing variables ?

JavaScript

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Q32. Difference between Let and Var in Javascript ?

JavaScript

Ans. Var scopes the variable to the nearest function whereas Let scopes the variable to nearest block.

For example -

function printNumbers() {
for(var i = 1; i < 3: i++){
console.log(i);
}

console.log(i); // works fine and will print 3 as i has a function scope and not local loop scope
}

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Q33. How can we create an arraylist of unique values ?

Core Java

Ans. We can put the value in a set to enforce uniqueness and then dum those value into an arraylist.

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Q34. Why wait(), notify(), notifyAll() methods are in Object class instead of Thread class?

Core Java

Ans. wait() and notify() methods are defined in Object class rather than Thread class.If wait() and notify() were on the Thread instead then each thread would have to know the status of every other thread and there is no way to know thread1 that thread2 was waiting for any resource to access.Hence, notify, wait, notifyAll methods are defined in object class in Java.

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Q35. Can the value of a static variable be changed ?

Core Java

Ans. Yes the value of a static variable can be changed. It's the final keyword that restrict the modification of value not static.

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Q36. What are the advantages and disadvantages of Lambda Expression ?

Core Java

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Q37. Write a unit test case using java 8.

JUnit

Ans. public List convertAllToUpperCase(List words) {
return words.stream().map(String::toUpperCase).collect(Collectors.toList());
}

@Test
public void testAllToUpperCase() {
List expected = Arrays.asList("JAVA8", "STREAMS");
List result = convertAllToUpperCase(Arrays.asList("java8", "streams"));
assertEquals(expected, result);
}

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Q38. Write a program to make an array act as a set.

Core Java

Ans. public Set convertArrayToList(T array[]) {
Set set = new HashSet<>(Arrays.asList(array));
return set;
}

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Q39. What is the use of defining equals , compareTo and hashcode methods in a class ? Where are they used ?

Core Java

Ans. equals, compareTo and hashcode are of use when the objects are used within collections.

Equals helps with collections that helps maintaining only unique objects ( like Set )

compare and compareTo helps with collections that helps maintaining objects in order ( TreeSet, TreeMap etc )

hascode helps with collections that facilitates hash searching ( like hashSet, hashMap etc )

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Q40. prototypal inheritance in Javascript

JavaScript

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