Core Java Interview Questions for Selenium tester

Hell Friends,

In this article we will discuss about Java interview Questions for Selenium Tester :

Write a Program to change the case of a String like "aBcD eF@ g" ?

Validate two String have same latters example x = "listen", y = "silent" ?

Write a Program to check String is palindrom using recursion ?

Write a Program to sort a String without using any function ?

How to find middle number from an integer array ?

How to find greatest Number from a integer array without using sorting?

find the greatest word from a String/sentance

write a program to remove duplicate character from a string ?

Write a program to find occurance of letter in a given string

Write a program to reverse the sentense

Write a program to reverse the Word in java

Write a program to sort the array in java

Write a program in java to find number is prime or not

Write a program to check the Word is palindrome or not in java

Write a program in java to remove first and last letter alternatively and print

Distinguise numbers & letter from a string, given "way2testing"

Find number of letter, number of digits and number of special character in a String

Reverse a String , without using any inbuild methods

Write a Java Program to check if the two strings are anagrams.

What is the output of below program?

Does constructor return any value?

a. Write a Program to change the case of a String like "aBcD eF@ g"

Answer :-

first we will check each character of string .
in this is upper case we will change it to lower case and vice-versa
now, we will change char to string and will append in output string using String Builder

Below is program

public class Streamdemo2 {

public static void main(String[] args) {

// WebDriver driver = new ChromeDriver();
String x = "aBcD eF@ g";
StringBuilder output = new StringBuilder();
for(int i=0; i<x.length(); i++){
if(Character.isUpperCase(x.charAt(i))){
char n = Character.toLowerCase(x.charAt(i));
output.append(Character.toString(n));
}

else if(Character.isLowerCase(x.charAt(i))){
char n = Character.toUpperCase(x.charAt(i));
output.append(Character.toString(n));
}else{

output.append(Character.toString(x.charAt(i)));
}
}
System.out.println(output);
}
}

Output :-

--------------------------------------

b. Validate two String have same latters example x = "listen", y = "silent" ?

Answer :-

first check whether both string have same length .
now sort both the string
now compare both the arrays

Below is program

public class matchstr {
public static void main(String[] args){
String x = "listen";
String y = "silent";
char[] s1 = x.toCharArray();
char[] s2 = y.toCharArray();
Arrays.sort(s1);
Arrays.sort(s2);
if(Arrays.equals(s1, s2)){
System.out.println("Both are same");
}
}
}

Output :-

--------------------------------------

0. Write a Program to check String is palindrom using recursion ?

Answer :-

We will check first character or String to last character.
check second character with second last character and so on
if matches then String is palindrome

Below is program

public class Package2 {
public static void main(String[] args) {
String x = "radar";
System.out.println("Is palindrome " + isPalindrome(x));
}
public static boolean isPalindrome(String str) {
if(str.isEmpty() || str.length() ==1) {
return true;
}
if(str.charAt(0) == str.charAt(str.length()-1)) {
return isPalindrome(str.substring(1, str.length()-1));
}
else {
return false;
}
}
}

Output :-

A. Write a Program to sort a String without using any function ?

Answer :-

First we will change the given string to character array.
Second we create a bubble sort function to sort the array
finally we will change the array to string

Below is program

public class Practice {
public static void main(String arg[]) {
String str = "way2testing";
char[] arr = str.toCharArray();
sortTheString(arr);
String sortedString = new String(arr);
System.out.println(sortedString);
}
public static void sortTheString(char[] c) {
boolean swapped;
do {
swapped = false;
for(int i = 0; i if(c[i]>c[i+1]) {
char temp = c[i];
c[i] = c[i+1];
c[i+1] = temp;
swapped = true;
}
}
}while(swapped);
}
}

Output :-

---------------------------------------------------------------------------

B. How to find middle number from an integer array ?

Answer :-

First we will sort the array.
Second if array length is odd then n/2 is middle one
if array length is even then middle number will be n/2 & n-1/2

Below is program

public class Practice {
public static void main(String arg[]) {
int[] x = {2, 5, 9, 11, 21, 6};
Arrays.sort(x);
for(int i =0; i System.out.println(x[i]);
}
if(x.length%2 != 0) {
System.out.println("Middle number is " + x[x.length/2]);
}
else {
System.out.println("Middle number is " + x[(x.length-1)/2]);
System.out.println("Middle number is " + x[(x.length)/2]);
}
}
}

Output :-

---------------------------------------------------------------------------

C. How to find greatest Number from a integer array without using sorting?

Answer :-

Create a variable to store any number from array
and compare it to other
if other is greater than this variable then assign this greater value to variable

Below is program

public class Practice {
public static void main(String arg[]) {
int[] x = {43, 2, 5, 9, 11, 21, 6};
int greatestNumber = x[0];
for(int i=1; i if(x[i]>greatestNumber) {
greatestNumber = x[i];
}
}
System.out.println("greatest number is " +greatestNumber);
}
}

Output :-

---------------------------------------------------------------------------

D. find the greatest word from a String/sentance ?

Answer :-

first break the sentance in String array
create two variable , one to store word length and one to store word
now simply compare each word to another and put greater one in variable

Below is program

public class Practice {
public static void main(String arg[]) {
String x = "I love testing mainly automation and little manual";
String[] words = x.split(" ");
String longestString = "";
int longlength =0;
for(int i =0; i<words.length-1; i++) {
if(words[i].length()> >words[i+1].length()) {
longestString = words[bi];
longlength = words[i].length();
}
}
System.out.println(longestString + " " +longlength);
}
}

Output :-

---------------------------------------------------------------------------

E. write a program to remove duplicate character from a string ?

Answer :-

We can use here collection, like LinkedHashSet or Treeset

Below is program

public class Practice {
public static void main(String arg[]) {
String str = "chandan";
Set set = new TreeSet();
for(int i =0; i<str.length(); i++) {
set.add(str.charAt(i));
}
System.out.println(set);
String s = "";
for(Character st : set) {
s = s + st;
}
System.out.println(s);
}
}

Output :-


---------------------------------------------------------------------------

0. Write a program to find occurance of letter in a given string

Answer :- First change the string in Character Array then for each character run a for loop to find another character in String.


Below is program, way 1

public class PracticeA {

public static void main(String args[]) {
String x = "aabbbccccdddee";

char[] ch = x.toCharArray();

Map<Character , Object> mp = new HashMap<Character, Object>();

for(int i = 0; i<ch.length; i++) {
int counter = 1;
if(mp.containsKey(ch[i])) {
System.out.println("letter already present");
}

else {
System.out.println("letter not present");
for(int j =0; j<ch.length; j++) {
if(ch[i]==ch[j]) {
mp.put(ch[i], counter);
counter++;
}
}
}
}
System.out.println(mp);
}
}
}

Output :- {a=2, b=3, c=4, d=3, e=2}


Below is program, way 2

public class Practice {
public static void main(String arg[]) {
String str = "i love my india";
String inputstr = str.replace(" ", "");
char[] c = inputstr.toCharArray();
Map occ = new HashMap();
for(char ch : c) {
if(occ.containsKey(ch)) {
occ.put(ch, occ.get(ch)+1);
}
else {
occ.put(ch, 1);
}
}
System.out.println(occ);
for(Map.Entry entry: occ.entrySet()) {
System.out.println(entry.getKey()+" " + "occured"+" " + entry.getValue());
}
}
}

Output :-

---------------------------------------------------------------------------

1. Write a program to reverse the sentense

Answer: First split the string by spaces (" "), then store in an Array and finally print the array in reverse order.

Below is program

public class Sentensereverse
{
static String str = "my name is chandan";
static String str3 = "";
public static void main(String[] args)
{
String s[] = str.split(" ");
for(int j=s.length-1;j>=0; j--)
{
System.out.println(j);
str3 = str3 + " "+s[j];
}
System.out.println(str3);
}
}

Output :- chandan is name my

---------------------------------------------------------------------------

2. Write a program to reverse the Word in java

Answer :- We will create a blank string variable and will break the input word in character by method charAt().

Below is program

public class Sentensereverse
{
public static void main(String[] args)
{
String str = "chandan";
String str2 = "";
for(int i = str.length()-1; i>=0; i--)
{
str2 = str2 + str.charAt(i);
}
System.out.println(str2);
}
}

Output :- nadnahc

---------------------------------------------------------------------------

3. Write a program to sort the array in java

Answer :- We will compare each element to rest of all elements if element is greater , then we will swap them.

Below is program

public class Sortarray
{
int[] arr = {4, 20, 9, 15, 7, 11};
public static void main(String args[])
{
Sortarray obj = new Sortarray();
obj.sarray();
}
public void sarray()
{
for(int i =0; i<arr.length; i++)
{
for(int j =0; j<arr.length; j++)
{
if(arr[i]<arr[j])
{
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
for(int element : arr)
{
System.out.println(element);
}
}
}

Output :- 4 7 9 11 15 20

---------------------------------------------------------------------------

4. Write a program in java to find number is prime or not

Answer :- If any number is divisible by only 1 or self then that number is known as prime number. .
So we will divide that number from 2 to just 1 digit before to testing number.
if remainder is zero then number is prime otherwise number is not prime.

Below is program

public class Test2
{
public static void main(String[] args)
{
Scanner scn = new Scanner(System.in);
System.out.println("Enter the number");
boolean flag = false;
int x = scn.nextInt();
if(x == 0 || x == 1)
{
System.out.println("Invalid number Entered");
}
else
{
for(int i = 2; i<=x/2; i++)
{
if(x%i == 0)
{
flag = true;
break;
}
}
if(flag)
{
System.out.println("Number is not prime");
}
else
{
System.out.println("number is prime");
}
}
}
}

Output :- NUMBER is prime

------------------------------------------------------------------------

5. Write a program to check the Word is palindrome or not in java

Answer :- Simply reverse the string and then compare new reversed string to test string, if both are same Strings are palindrome .

Below is program

public class Test2
{
public static void main(String args[])
{
Scanner scn = new Scanner(System.in);
System.out.println("Enter the string");
String test = scn.next();
String ptest = "";
for(int i = test.length()-1; i>=0; i--)
{
ptest = ptest + test.charAt(i);

}
System.out.println(ptest);
if(test.equalsIgnoreCase(ptest))
{
System.out.println("String is palindrome");
}
else
{
System.out.println("String is not palindrome");
}
}
}

Output :- Enter the string
refer
refer
String is palindrome


---------------------------------------------------------------------------

Write a program in java to remove first and last letter alternatively and print

Answer :- The above problem is easy, just a combination of three logics
First:, remove first letter from String
Second:, remove last letter from String
Third:, call above above methods alternatively
and combine all three logic with any loop to get the answer

Below is program

public class CscPractice {
public static void main(String args[]) {
String x = "chandan";
do {
x = firstcut(x);
System.out.println(x);
if(x.length()>1) {
x = lastcut(x);
System.out.println(x);}
}
while(x.length()>0);
}
public static String firstcut(String s) {
s = s.substring(1, s.length());
return s ;
}
public static String lastcut(String s) {
s = s.substring(0, s.length()-1);
return s;
}
}

Output :-

---------------------------------------------------------------------------

. Distinguise numbers & letter from a string, given "way2testing"

Answer :- First we will get the character of string and for each character we will check whether it is number or letter by method Character.isDigit(), then we will put the appropraite character in different String or array.

Below is program

public class ChandanSP
{
public static void main(String args[])
{
String num = "";
String purestr = "";
String x = "way2testing";
for(int i = 0; i<x.length(); i++)
{
char ch = x.charAt(i);
if(Character.isDigit(ch))
{
num = num + ch;
}
else
{
purestr = purestr +ch;
}
}
System.out.println(purestr);
System.out.println(num);
}
}

Output :-
waytesting
2

---------------------------------------------------------------------------

. Find number of letter, number of digits and number of special character in a String

Answer :- First we need to convert the String into character array(.toCharArray())
now with the help of below two character class method, we can find letter and numbers and remaining will be the special character
Character.isDigit(), Character.isLetter() .

Below is program

public class JavaPractice {
public static void main(String args[]) {
String S = "123abcde@#$%&";
int number = 0;
int letter = 0;
int special = 0;
char c[] = S.toCharArray();
for(char a : c) {
if(Character.isDigit(a)) {
number++;
}
else if(Character.isLetter(a)) {
letter++;
}
else {
special++;
}
}
System.out.println("Numbers are " +number);
System.out.println("letters are " +letter);
System.out.println("Special are " +special);
}
}

Output :-
Numbers are 3
letters are 5
Special are 5

---------------------------------------------------------------------------

Q. Reverse a String , without using any inbuild methods

Answer :- Convert the string into byteArray, then reverse the array
and by using below method change array to String String s = new String(byte)

. Below is program

public class JavaTutorial {
public static void main(String args[]) {
String x = "Chandan";
byte[] bytes = x.getBytes();
byte num[] = new byte[x.length()];
for(int i = 0; i<bytes.length; i++) {
System.out.println(bytes[i]);
num[i] = bytes[bytes.length-(i+1)];
}
for(byte xx : num) {
System.out.println(xx);
}
String m = new String(num);
System.out.println(m);
}
}

Output :-
110
97
100
110
97
104
67
nadnahC


---------------------------------------------------------------------------

Write a Java Program to check if the two strings are anagrams.

Answer : first we will check the length of both the string , if length is equal the we will sort the String (using char array) then we will compare both the char array.

Below is program

public class Package2 {
public static void main(String[] args) {
String x = "i like titanic";
String y = "iic like titan";
if(x.length() == y.length()) {
char[] xarray = x.toCharArray();
char[] yarray = y.toCharArray();
Arrays.sort(xarray);
Arrays.sort(yarray);
if(Arrays.equals(xarray, yarray)) {
System.out.println("String are anagrams ");
}
else {
System.out.println("String are not anagrams ");
}
}
else {
System.out.println("String are not anagrams ");
}
}
}

Output :-

---------------------------------------------------------------------------

What is the output of below program.

Answer : in first print statement one number will be added to another then when string come into existance then whole will be treated as string and concatinated.
in second case first string come into existance then next numbers will be treated as String and will be concatinated
Below is program

class Practice2
{
public static void main (String args[])
{
System.out.println(9 + 5 + "way2testing.com");
System.out.println("way2testing.com" + 9 + 5);
}
}

Output :-

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0.What is Java?
Java is a programming language and computing platform first released by Sun MicroSystems in 1995.

1. What is a JVM?
JVM is Java Virtual Machine which is a run time environment for the compiled java class files.

2. Does Java support multiple inheritance?
Java doesn't support multiple inheritance.

3. What is the most important feature of Java?
Java is a platform independent language.

4. What is difference between Path and Classpath?
Path and Classpath are operating system level environment variales. Path is used define where the system can find the executables(.exe) files and classpath is used to specify the location .class files.

5. What are instance variables?
Instance variables are those which are defined at the class level. Instance variables need not be initialized before using them as they are automatically initialized to their default values.

6. What is a pointer and does Java support pointers?
Pointer is a reference handle to a memory location. Improper handling of pointers leads to memory leaks and reliability issues hence Java doesn't support the usage of pointers.

7. What is the return type of the main() method?
Main() method doesn't return anything hence declared void.

8. What are local variables?
Local variables are those which are declared within a block of code like methods. Local variables should be initialized before accessing them.

9. Is Java a pure object oriented language?
Java uses primitive data types and hence is not a pure object oriented language.

10. Is JVM platform independent?
JVM's are not platform independent. JVM's are platform specific run time implementation provided by the vendor.

11. Can a main() method be overloaded?
Yes. You can have any number of main() methods with different method signature and implementation in the class.
but only java defined main() method "public static void main(String[] args)" will be executed

12. What is the base class of all classes?
java.lang.Object

13. What do you mean by platform independence?
Platform independence means that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux,Solaris,etc).

14. Are arrays primitive data types?
In Java, Arrays are objects.

15. What is the difference between a JDK and a JVM?
JDK is Java Development Kit which is for development purpose and it includes execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.

16. Does the order of public and static declaration matter in main() method?
No. It doesn't matter but void should always come before main().

17. What is the impact of declaring a method as final?
A method declared as final can't be overridden. A sub-class can't have the same method signature with a different implementation.

18. Can a class be declared as protected?
A class can't be declared as protected. only methods can be declared as protected.

19. How to define a constant variable in Java?
The variable should be declared as static and final. So only one copy of the variable exists for all instances of the class and the value can't be changed also. static final int PI = 2.14; is an example for constant.

20. Which package is imported by default?
java.lang package is imported by default even without a package declaration.

21. What is the argument of main() method?
main() method accepts an array of String object as argument.

22. Can a source file contain more than one class declaration?
Yes a single source file can contain any number of Class declarations but only one of the class can be declared as public.

23. What is the access scope of a protected method?
A protected method can be accessed by the classes within the same package or by the sub classes of the class in any package.

24. Can a class declared as private be accessed outside it's package?
Not possible.

25. Why is the main() method declared static?
main() method is called by the JVM even before the instantiation of the class hence it is declared as static.

26. What is the purpose of declaring a variable as final?
A final variable's value can't be changed. final variables should be initialized before using them.

27. What is a package?
Package is a collection of related classes and interfaces. package declaration should be first statement in a java class.

28. Can a main() method be declared final?
Yes. Any inheriting class will not be able to have it's own default main() method.

29. I don't want my class to be inherited by any other class. What should i do?
You should declared your class as final. But you can't define your class as final, if it is an abstract class. A class declared as final can't be extended by any other class.

30. Should a main() method be compulsorily declared in all java classes?
No not required. main() method should be defined only if the source class is a java application.

31. When will you define a method as static?
When a method needs to be accessed even before the creation of the object of the class then we should declare the method as static.

32. What is the importance of static variable?
static variables are class level variables where all objects of the class refer to the same variable. If one object changes the value then the change gets reflected in all the objects.

33. How is final different from finally and finalize()?
final is a modifier which can be applied to a class or a method or a variable. final class can't be inherited,final method can't be overridden and final variable can't be changed.
finally is an exception handling code section which gets executed whether an exception is raised or not by the try block code segment. finalize() is a method of Object class which will be executed by the JVM just before garbage collecting object to give a final chance for resource releasing activity.

34. I want to print "Hello" even before main() is executed. How will you achieve that?
Print the statement inside a static block of code. Static blocks get executed when the class gets loaded into the memory and even before the creation of an object. Hence it will be executed before the main() method. And it will be executed only once.

35. Can we declare a static variable inside a method?
Static variables are class level variables and they can't be declared inside a method. If declared, the class will not compile.

36. Can a abstract class be defined without any abstract methods?
Yes it's possible. This is basically to avoid instance creation of the class.

37. Can you give few examples of final classes defined in Java API?
java.lang.String, java.lang.Math are final classes.

38. Can a abstract class be declared final?
Not possible. An abstract class without being inherited is of no use and hence will result in compile time error.

39. Can you create an object of an abstract class?
Not possible. Abstract classes can't be instantiated.

40. What are the restriction imposed on a static method or a static block of code?
A static method should not refer to instance variables without creating an instance and cannot use "this" operator to refer the instance.

41. Can a Class extend more than one Class?
Not possible. A Class can extend only one class but can implement any number of Interfaces.

42. Class C implements Interface I containing method m1 and m2 declarations. Class C has provided implementation for method m2. Can i create an object of Class C?
No not possible. Class C should provide implementation for all the methods in the Interface I. Since Class C didn't provide implementation for m1 method, it has to be declared as abstract. Abstract classes can't be instantiated.

43. Can a class be defined inside an Interface?
Yes it's possible.

44. Can an Interface extend another Interface?
Yes an Interface can inherit another Interface, for that matter an Interface can extend more than one Interface.

45. What is use of a abstract variable?
Variables can't be declared as abstract. only classes and methods can be declared as abstract.

46. Can an Interface be defined inside a class?
Yes it's possible.

47. What is an Abstract Class and what is it's purpose?
A Class which doesn't provide complete implementation is defined as an abstract class. Abstract classes enforce abstraction.

48. Can an Interface be final?
Not possible. Doing so so will result in compilation error.

49. Can an Interface implement another Interface?
Interfaces doesn't provide implementation hence a interface cannot implement another interface.

50. Why does Java not support operator overloading?
Operator overloading makes the code very difficult to read and maintain. To maintain code simplicity, Java doesn't support operator overloading.

51. Is there any difference between an argument and a parameter?
While defining methods, you pass variables which you refer as parameters. And when you call these methods and pass values for the variables then they are phrased as arguments.

52. How your program would behave if you declare the main method as private?
It would get compiled correctly but will throw the error "Main method not public." at runtime.

53. Q: What difference you see between pass by reference and pass by value in Java?
Pass by reference indicates, passing the address itself rather than passing the value. Pass by value means is giving a copy of the value.
Example : Actions action = new Actions(driver);

54. Can you compile a Java class successfully without having the main method?
Yes, we can compile, but it won't run. The

method works as the startup function for a Java class, and the JVM calls it for the program execution.

55.What do you make of System, out and in the function System.out.println()?
System -> A predefined final class,
out -> PrintStream object and,
The -> built-in overloaded method of the out object.

56.Q: How would you prove that an array is not null but is empty?
Call the . It will print 0. That suggests that the array is empty. If it would've been null then, it would've thrown a on calling the .

57. Q: Does constructor return any value?

yes, The constructor implicitly returns the current instance of the class (You can't use an explicit return type with the constructor).

> 58. Q: What do you understand of Garbage Collection and how to call it explicitly?
If the object is no longer belong to any variable, Java automatically reclaims the memory. This process is known as garbage collection. You can use the method to call it explicitly.
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